final highway copy

8/12/2019 Final Highway Copy

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KYAMBOGO UNIVERSITY

FACULTY OF ENGINEERING

DEPARTMENT OF CIVIL AND BUILDING ENGINEERING

BACHELOR OF ENGINEERING IN CIVIL AND BUILDING ENGINEERING

YEAR 3

SEMESTER TWO

CE 323 HIGHWAY ENGINEERING I

GROUP ASSIGNMENT

MEMBERS

NDOZIREHO RONNIE 07/U/187/ECD/GV

WEPUKHULU EFULONI JOSHUA 07/U/2980/ECD/PD

KANABU EVANS 08/X/1936/ECD/PD

MURA DANIEL 06/U/169/ECD/GV

MURUNGI ELIZABETH 07/U/186/ECD/GV

LANGOLTUM PETER 07/U/09/ECD/PD/NPT

ACIDRI SAMUEL 08/U/1931/ECD/PD

LECTURER: MR OKELLO EUGENE FRANCIS


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TABLE OF CONTENTS

1(a). Role of road infrastructure in economic development ....3

(b). Advantages and disadvantages of road transport over other modes.....5

(c). Information expected in a feasibility study report.....8

2(a). Necessity of economic evaluation of highway projects....11

(b). Major differences between economic and financial analysis..11

(c). Criteria followed in selection of an appropriate economic evaluation method....12

(d). Economic analysis of given road.....13

3(a). Information expected from a desk study in a reconnaissance survey...15

(b). Considerations influencing choice of centre line in preliminary location survey....17

(c). Benefits analyzed in the feasibility study...17

4(a). Considerations in drawing up geometric standards for a country................................19(b). Super elevation.........................................................................................................19

(c). Transition curve..........................................................................................................20

(d). Super elevation calculation.........................................................................................20

5(a). Vertical alignment......................................................................................................22

(b). Factors considered in the design of vertical curves.......................................................22

(c). Design vehicle, design speed, speed limit....................................................................23

(d). Parabolic vertical curve calculation..............................................................................23

6(a). Cross section elements..............................................................................................25

(b). Preliminary phase of design process of a junction........................................................28

(c). T-junction design........................................................................................................28

7(a). Characteristics that render roundabouts most effective.............................................31

(b). Design features of roundabouts.................................................................................31

(c). Roundabout design....................................................................................................32

8(a). Considerations in the choice between rigid and flexible pavements...........................35

(b). Meaning of pavement structure terms....................................................................... ....35

(c). Flexible pavement design...................................................................................................37


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Question 1 (a.)

The word transport originates from the Latin word; transportare

i) Transmeaning across, over or through, andii) Portaremeaning carry.Thus transportation can be defined as ... the act of carrying somebody or something from one

place to another, usually in a vehicle (Microsoft Student with Encarta Premium [DVD], 2008). ...

Transport infrastructure refers to the fixed installations necessary for transport. In relation to

Uganda, the major elements of the road infrastructure consist of the following;

roads which may be earth roads, gravel roads or paved roads, terminals such as bus stations, warehouses, trucking terminals, refuelling depots including fuel stations.

Other elements of Ugandas road infrastructure include;

earth retaining structures, bridges, culverts and other drainage facilities, safety systems such as roadside barriers and speed limiting devices such as speed

humps,

road signs, road lighting, and noise barriers.

Economic development refers to the ... promotion of more intensive and more advanced

economic activity through such means as education, improved tools and techniques, more available

financing, better transportation facilities, and creation of new businesses (Microsoft Student with

Encarta Premium [DVD], 2008). ...

Transportation is vital component of any societys growth and development. According toMathew (2006), it exhibits a very close relation to the style of life, the range and location of activities

and the goods and services which will be available for consumption. ...

Ugandas road infrastructure plays a number of roles in relation to Ugandas economic

development. These roles include the following:

I. Development of The Agriculture Sector:The agricultural sector requires a constant supply of agricultural inputs such as pesticides,

fertilizers, tools and equipment, labour, seeds and so on. The agricultural sector would also be

practically redundant without access to markets.

Ugandas road infrastructure promotes the development of the agricultural sector by fulfilling

the above essential needs of the agricultural sector.

II. Facilitation of Social Activities, Market Growth And Land Usage:Ugandas road infrastructure enables social activities to take place, such as the provision of

education and health services, sensitization workshops, political or religious rallies and so on.

III. Facilitation of Administration:


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to carry out logistics operations. For example, it is difficult for a paramilitary organisation to take

over areas of Uganda due to the rapid response of Ugandas military.

XI. Development of the Tourism Sector:Without adequate road infrastructure, Ugandas potential earnings from the tourism sector will

not be realised as tourists will not be able to access the tourist sites and areas of scenic beauty.Ugandas road infrastructure makes the tourists experience convenient and comfortable by

providing easy access to tourist sites such as the at the source of the Nile at Jinja, Queen

Elizabeth National Park and Kabalega National Park. In this way Ugandas road infrastructure

promotes the tourism sector.

XII. Bridging The Gap Between The Producers & Consumers:The production of goods or provision of services does not always coincide, in terms of location,

with that of consumers. This problem is overcome by Ugandas road infrastructure, which

enables the movement of products, consumers or both to a common meeting point for trade to

occur.

XIII. Facilitation Of The Exploitation Of Natural Resources:Since Uganda is a landlocked country, the most convenient means of transporting exports from

the exploitation of natural resources is through over land transport. The road infrastructure of

Uganda enables natural resources such as plant products, animal products, mineral deposits and

soon fossil fuels, to be transported to foreign markets, thereby earning foreign exchange and

promoting economic development.

XIV. Creation of Employment:The construction and maintenance of Ugandas road infrastructure is highly labour intensive.

This provides much needed employment to both skilled and unskilled labour as well as

conserving foreign exchange which would have been spent on expensive mechanical equipment.

XV. Balanced Development:A well distributed road network allows more balanced distribution of services and hence a more

balanced development of the country, keeping in view the special needs of inaccessible areas

and underdeveloped societies in the country.

Question 1 (b.)

The advantages of road transport over other modes of transport include the following;

I. High Employment PotentialRoad transport has a high employment potential for both skilled and non-skilled labour

compared to other modes of transport. Road transport is more labour based in its construction,operation and maintenance compared to other modes of transport.

II. Lower Initial CostsCompared to other modes of transport such as railway, it is initially less costly to construct a

road. Also in road construction, it is possible to carry out stage construction, which may not be

the case for other modes of transport.


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III. More Economical For Short HaulsRoad transport is more economical for moving goods and people through short distances

compared to other modes of transport. This is because for other modes of transport it is not

cost-effective to construct terminals within a short distance of each other, for example railway

stations for railway transport or airports for air transport.

IV. Services Unique to the IndividualOther modes of transport usually do not offer services tailored to suit individual needs or

preferences. However, with road transport, road users are provided with services suited to the

individual, such as individual insurance cover, care of cargo and so on.

V. Less Complex Packaging & RestraintsRoad transport affords road users the ability to transport goods using less complex packaging

and restraints compared to other modes of transport. Other modes of transport are subject to

greater vibrations and oscillations during transport, this poses a greater risk of damage to cargo,

thus the packaging and restraints for such modes must be more comprehensive.

VI. Door to Door ServicesRoad transport affords road users the ability to utilise almost any part of the road network as a

starting or ending terminal. Goods and services can be transported from the initial point to the

final point without having to make additional interconnections between. This enables road users

to avoid inconvenient delays and confusion and additional costs incurred when using modes of

transport that have fixed and limited terminals.

VII. Quick &Assured DeliveriesIf other modes of transport are used, it becomes uneconomical to transport goods when the

vehicle is not fully loaded. Thus there are always time constraints with other modes of transport

as the vehicle must be fully loaded before departing. In order to enjoy economies of scale these

loads are usually large and hence it takes the vehicle some time to fill. However, the vehicles

used in road transport have much smaller capacities and hence take less time to fill before

departing to the final destination.

VIII. FlexibilityRoad transport affords road users the opportunity to select from a number of available routes to

suit their particular needs; however other modes of transport are usually fixed in their choice of

transport routes.

Also road transport enables road users to move at their own convenience. They are free from

the rigours of timetables. However, the movement goods and people in other modes of

transport are controlled by schedules, which may not always match demand nor be convenient.

IX. Personalized TravelRoad transport affords road users the ability to travel by a vehicle of their choosing according to

factors such as their economic constraints, environmental concerns, space requirements,

comfort preferences and availability of transport vehicles. These transport vehicles may non-

motorised human powered means, non-motorised animal powered means or motorised means

of transport.


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X. Wide Geographical CoverageBecause of the low construction costs and lower technical restraints imposed on road traffic by

terrain compared to other modes of transport, road transport has a wider geographical

coverage compared to other modes of transport. It would be very uneconomical to construct

such extensive geographical coverage using another mode of transport.

XI. Ease of Response to Road AccidentsAccidents occurring on or near roads are easier for emergency services to reach compared to

other modes of transport.

The disadvantages of road transport include the following;

I. High Maintenance Costs for Frequent MaintenanceRoads are affected to a great degree by climatic factors such as rainfall and variations in

temperature. Coupled with repetitive stresses imposed on the road pavement layers by traffic,

roads tend to deteriorate faster than other modes of transport such as rail transport. Thus a

higher frequency of maintenance work is needed for road transport, resulting in high

maintenance costs for road transport.

II. SafetyDue to the large volume of road users and the variety of vehicles operating on the roads, as well

as the effect of climatic factors on road transport, there is a large volume of road accidents

compared to other modes of transport. This has led to economic losses in the form of loss of

skilled labour, loss of materials and other inputs, delays

III. High Energy ConsumptionThe energy consumption per passenger kilometre and per tonne kilometre has been found to be

higher with road transport compared to other modes of transport. This is because in other

modes of transport, the energy costs are split with a larger number of transport users per

journey. For example a car moving from A to B may carry only 5 people while a train moving

between the same terminals may carry 1000 people.

IV. Environmental pollutionIn urban areas the main source of pollution and noise is road transport. This poses significant

problems such as unwanted noises and vibrations, poor air quality, formation of acid rain and is

also said to be a contributor to global warming. Other examples of environmental degradation

include the destruction of areas of scenic beauty as roads are constructed.

V. Long HaulsOther modes of transport are better suited to transport goods and services across large

distances compared to road transport. For example, water transport can be used transport

exceedingly larger amounts of cargo and personnel than road transport. This is especially useful

for large, bulky non-perishable products. Also air transport can cover a large distance in a much

shorter time and thus is more suited to meet urgent transport needs such as; mail delivery,

transport of perishable goods, transport of important cargo, transport of humanitarian items

and also transport of military units.

VI. Parking Problem


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Due to the large volume of road users in urban areas, providing adequate parking for all of the

road users is not always possible. This causes a number of problems such as narrower streets,

which in turn cause encourage congestion and subsequent delays.

Question 1 (c.)

The feasibility study report marks the end of the appraisal process and should recommend whether the

project should go ahead, and to what standards it should be built (ORN 5: A Guide to Road Project

Appraisal, 1988).

The kind of information expected to be found in a feasibility study report of any given road link would

include the following;

1. Definition of objectives:A road project should comply with the objectives of a national or regional transport plan. The

project's objectives must be defined in order to provide the basic framework for the analysis.

The objectives of the road project being studied may be ... to support some other

developmental activity, to provide fundamental links in the national or a district road network,

or perhaps to meet a strategic need. Alternatively, a road improvement may be proposed to

increase the structural or volumetric capacity of an existing road to cope with higher trafficflows. Often, there will be multiple objectives (ORN 5: A Guide to Road Project Appraisal, 1988).

...

2. Determination of alternative ways of meeting objectives:A number of proposed solutions are determined in context of the particular needs and problems

encountered. Possible alternatives include;

Upgrading a road in order to increase capacity. New construction of a road. Rehabilitation in case the road has deteriorated beyond the condition at which

overlaying is a satisfactory engineering alternative. Reconstruction of the road, possibly to provide a new alignment . Stage construction, or Maintenance in order to ensure that the road does not 'fail' before the end of its design

life.

3. Preliminary considerations:A number of preliminary considerations must be made and these include;

Analysis period and design life, this impacts the design standards of the road as well asthe residual value of the road at the end of the economic analysis period.

Uncertainty and risk, the feasibility study should be carried out with recognition ofuncertainties in the future and make provisions to minimise risk.

Choice of technology, a choice must be made between using technology dominated bymechanical equipment or dominated by labour.

Institutional issues, the aspects that need to be considered are ... the organisation,staffing, training, procedures, planning, maintenance, funding and controls within the


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agency responsible for the project, and also within other agencies who may need to

make an input to the project (ORN 5: A Guide to Road Project Appraisal, 1988). ...

Socio-economic considerations, the aspects that need to be considered are socialchanges, the effect of construction on the indigenous community, the effect of the

project on road accidents, severance of the community, special needs of minority

groups, expertise and resources of the local design organisation and contracting

industry, the reliability of data on the local social environment, the site conditions and

climate.

Environmental conditions, the possible environmental effects of the project should beconsidered in qualitative terms. Environmental problems raised may include air

pollution, noise and vibration, visual intrusion and destruction of ecosystems.

4. Assess traffic demand:For the purposes of geometric design and the evaluation of economic benefits, the volume and

composition of current and future traffic needs to be known in terms of cars, light goods

vehicles, trucks, buses, non-motorised vehicles, and so on (ORN 5: A Guide to Road ProjectAppraisal, 1988).

5. Design and cost different options:The costs involved in the project are based on a design carried out to an appropriate level of

detail. The road design process consists of the four following phases.

Route location, the corridor is normally chosen to balance maintaining user benefits byproviding the shortest route consistent with engineering constraints of topography,

ground conditions, drainage, structures and the location of road building materials (ORN

5: A Guide to Road Project Appraisal, 1988).

Pavement design, this primarily deals with the choice of materials and their thicknessfor each pavement layer.

Geometric design, this involves the selection of suitable horizontal and verticalalignments and road widths.

Design of structures, this deals with earth retaining systems, drainage systems andspecial provisions for erosion control as well as structures which allow the road to cross

or be crossed by rivers, water courses, railways and other roads.

6. Determine benefits for each alternative:Estimates are made, not only of the costs connected with the project, but also of the benefits

that are expected to occur.

Benefits normally considered are ... direct savings on the costs of operating vehicles, economies

in road maintenance, time savings by travellers and freight, reduction in road accidents, and

wider effects on the economic development of the region (ORN 5: A Guide to Road Project

Appraisal, 1988). ...

7. Economic analysis and comparison of alternatives:


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A cost-benefit analysis is carried out using the NPV (Net Present Value) or the IRR (Internal Rate

of Return) method, in order to ensure that an adequate return in terms of benefits results from

making a capital investment.

8. Recommendations:The report will make recommendations on whether the project should go ahead, and to whatstandards it should be built may also recommend alternative designs or approaches to the

project that would increase the rate of return in those areas where the original project is not

viable.

Depending on who the report is being written for, some aspects will have been covered in

greater depth than others and the recommendation will be delivered in the context of those

aspects.


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Question two

a) Purposes and significance of an economic evaluation Economic evaluation of project cycles helps in determining the extent to which the

project will contribute to the goals of raising the standard of living of the people and

their general welfare.

Economic evaluation also provides for a systematic and unbiased procedure forselecting different schemes for implementation.

Economic evaluation also ensures that the most worthwhile projects are given thehighest priority.

To decide whether the scheme under consideration is worth the investment at all. To rank schemes competing for scarce resources in order of priority. To compare various alternative schemes, with the most economical of all being

selected.

To assist in phasing the programme (stage construction) depending on the availability ofresources.

b) Major differences between economic analysis and financial analysis Financial analysis of a project estimates the profits accruing to the project operating

entity whereas economic analysis is used to measure the effect of the project on the

national economy (overall benefits as compared to the costs)

For a project to be economically viable, it must be financially sustainable as well aseconomically efficient. Therefore the economical benefits of a project cannot be

realized if the project is not financially sustainable.

Both types of analysis are conducted in monitory terms, the major difference being inthe definition of costs and benefits. In financial analysis, all expenditures incurred underthe project and revenues resulting from it are taken into account whereas economic

analysis attempts to access the overall impact of a project in improving the economic

welfare of all the citizens of the country concerned.

Economic analysis also differs from financial analysis in terms of; the breath of theidentification and evaluation of inputs and outputs, and the measure of costs and

benefits.

Economic analysis involves all members of the society and measures the positive andnegative impacts of the project in terms of the willingness and ability to pay for the units

of increased consumption and to accept compensation for the foregone units of

consumption rather than the actual prices paid as is the case with financial evaluations.

In financial evaluation, we consider taxes, insurance premium and inflation rate whereasthey are not considered in economic evaluations.


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c) Criteria to be followed in coming up with an appropriate evaluation methodComing up with an appropriate evaluation method is a relatively complex process however some of the

criteria given below may help guide the processes.

The requirements or conditions imposed by the financing agency of the project: Somefinancial agencies may dictate the method of evaluation so in the event that the project is

accepted, the specific method shall have to be used

The local practice and experience: Sometimes the local experience may favour a particularmethod of evaluation. Such that if a particular method is not dictated, the adopted method will

by default be used

Technology involvedin the given method; some of the methods involve complex computationsthat may require a certain level of technology.

The level of accuracy: Some methods like the internal rate of return method require a veryhigh level of accuracy. Other methods like the benefit cost ratio where the discount rate is

assumed are not as accurate. Depending on the lending agency or the level of accuracy

required, a particular method may be chosen.

The problem type to be decided on: Here, the decision of the type design standards and/oralignment of the road to be desired among other parameters like the determination of the

most appropriate timing of the investment and/or prioritisation of the most appropriate road

projects is made.

The type of project: consider a case where the project to be implemented is say a newconstruction/upgrading, reconstruction/rehabilitation, stage construction, or maintenance

projects, then we have to have to focus on the feasibility and urgency of constructing the road

basing on the capacity and benefit to be experienced in ratio of time.

For example, the FYRR is suited to an upgrading, rehabilitation since these projects are majorly

time constrained that is to say; the date/time at which the project is needed is a major

consideration since there is already an existing alternative.

However, for reconstruction or new construction projects, NPV, benefit cost ratio and IRR arepreferable methods since the existing option is unsuitable or there is no alternative

respectively.

The objectives of the project:The objectives of a project must be reflected by the benefits tobe included in the analysis. While the objectives of inter-urban trunk road projects normally is

to reduce vehicle operating costs and road maintenance costs, the objectives of rural access

road projects may include improving access to social services, stimulating agricultural

productions, etc.

The time, economic resources, skills and data available:For most projects, an analysis periodof 15 years from the date of opening is appropriate but, this should be tested by the

evaluation. Choosing the same analysis period as the design life of the pavement of a pavedroad simplifies the calculation of the projects residual value.


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d) Economic evaluation problemGiven data

Total length of existing road = 30km

Cost of improving an existing road = US$ 2, 000, 0000

Present traffic consists of:

(a) Commercial vehicles per day = 2000(b) Cars per day = 1500(c) Two wheelers per day = 1200(d) Total vehicles per day = 4700

Cost of operation (US$/km) on the existing road and improved road:

Existing road Improved road

(a) Commercial vehicle 5.00 4.00(b) Cars 3.00 2.50(c) Two wheeler 0.60 0.50

The accident rate on existing road and improved road is as under:(a) Existing road = 1.5 per mil- veh- km(b) Improved road = 1.0 per mil- veh-km(c) The cost of one accident = US$ 100,000

Growth rate of traffic is 10% p.a

The annual maintenance costs per km are:

(a) Existing road = US$ 30, 0000(b) Improved = US$ 40,0000

The analysis period is 10yrs

The discount rate is 12%

Calculation

Present Flow per year (mil. Veh- km/yr):

Commercial vehicles 200036530 = 21.90

Car 150036530 = 16.40

Two wheeler 120036530 = 13.14

Total 51.44

Predicted flow in 4thyear (mil. Veh- km/yr):

Commercial cars: 21.90(1.1) ^4 = 32.07

Car 16.40(1.1) ^4 =23.97

Two wheeler cars 13.14(1.1) ^4=19.23

Total 75.27

Operation cost benefit:Predicted operation cost in 4thyear:

Commercial cars: 132.0710^6 = 32.0710^6

Cars: 0.524.0610^6 = 12.0610^6

Two wheeler car: 0.119.2310^6 = 1.9210^6

Total = 45.98 10^6

Accident benefit:

4thyear (1.51.0) 75.27100,000 = 3763500


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BENEFITS Cost

year Flow(F)

Mil.

Veh-

km/yr

Accident

cost

savings

US$/yr

(106)

Operating

cost saving

US$/yr

(106)

Total

user

benefits

US$/yr

(106)

Discounted

Benefits

(PVB)

US$/yr

(106)

Construction

&

maintenance

cost US$/yr

Discounted

cost, (PVC)

US$/yr

1 20,000,000 17857142.86

2 20,000,000 15943877.55

3 20,000,000 14235604.96

4 75.27 3.764 45.98 49.744 31.613 300,000 190655.4235

5 82.8 4.14 50.59 54.73 31.055 300,000 170228.05676 91.08 4.55 55.62 60.17 30.483 300,000 151989.3364

7 100.23 5.01 43.31 48.32 21.857 300,000 135704.7646

8 110.23 5.52 45.92 51.44 20.775 300,000 121164.9684

9 121.26 6.06 52.38 58.44 21.074 300,000 108183.0075

10 133.35 6.67 81.43 88.1 28.365 300,000 96591.97098

11 146.73 7.34 89.61 96.95 27.870 300,000 86242.83123

12 161.4 8.07 98.57 106.64 27.371 300,000 77002.52788

13 177.51 8.87 108.42 117.29 26.879 300,000 68752.25704

TOTAL 267.348 TOTAL 49243140.51

Computation of NPV & B/C Ratio:

NPV = = 267,348,00049,243,140.51 = US$ 218,104,859.5B/C Ratio = / = = 5.43Concluding remarks:

All the above indicators point to the economic strength of the project under examination. Its NPV at just

over US$ 218 million is strongly positive and B/C ratio of 5.43 is well in excess of unity.


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Question 3aThe Desk study is the first step in the reconnaissance survey. It is a preliminary study of the

bands/corridors being evaluated within the region. Some information may already publicly available at

low cost (as compared with the cost of carrying out, say, new subsurface investigations) at government

institutions such as the ministry of works having been obtained from previous similar projects around

the area. A good desk study will result in great savings in both time and resources, as it helps ensure the

early recognition of difficult routes and allows for better planning and interpretation of the subsequent

detailed site investigations.

The following is a general check-list of the types of information that might be gathered for a desk study;

1. General land survey:(a) Location of site on published maps and charts.

(b) Dated air photographs.

(c) Site boundaries, outlines of structures and building lines. This is especially useful in planning

roads around developed areas where existing buildings and other structures restrain the possible

road path.

(d) Ground contours and natural drainage lines.(e) Above-ground obstructions to view and flying, e.g. transmission lines.

(f) Indications of obstructions below ground. These are mainly in the form of service conduits and

information regarding these may be obtained from the relevant service providers i.e. telephone,

power and water.

(g) Records of differences and omissions in relation to published maps.

(h) Positions of survey stations and benchmarks (the latter with reduced levels). The main purpose

of these stations is to monitor the location of the centreline accurately as even the most modern

survey equipment has limited accuracy over long distances.

(i) Appropriate meteorological information.

2. Permitted use and restrictions:(a) Planning and statutory restrictions applying to the particular areas under District and CountryPlanning Acts administered by the appropriate local authorities.

(b) Local authority regulations on planning restrictions, listed buildings and building by-laws; (c) (d)

Rights of light, support and way including any easements.

(e) Tunnels, mine workings (abandoned, active and proposed), and mineral rights.

(f) Ancient monuments, burial grounds, etc.

(g) Prior potentially contaminative uses of the site and of adjacent areas (landfills).

(h) Any restrictions imposed by environmental and ecological considerations, e.g. sites of special

scientific interest e.g. wetlands, bird sanctuaries, game reserves etc.

3. Approaches and access (including temporary access for construction purposes):(a) Road (check ownership);

(b) Railway

(c) By water4. Ground conditions:

(a) Geological maps, obtainable from Entebbe Geological Centre.

(b) Geological memoirs.

(c) Flooding, erosion, landslide and subsidence history. This is especially important in hilly terrain

which is highly susceptible to failure of this sort.

(d) Data held by central and local governmental authorities.

(e) Construction and investigation records of adjacent sites.


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(f) Seismicity.

5. Sources of material for construction:(a) Natural materials. These must be analysed for quality to ensure durable construction.

(b) Tips and waste materials.

(c) Imported materials and transport cost considerations.

6. Drainage and sewerage:(a) Names of the sewerage, land drainage and other authorities concerned, and their by-laws.

(b) Locations and levels of existing systems (including fields, drains and ditches), showing sizes of

pipe and whether they are foul, storm water or combined

(c) Existing flow quantities and capacity for additional flow.

(d) Liability to surcharging.

(e) Charges for drainage facilities.

(f) Neighbouring streams capable of taking sewage or trade effluent provided that they are purified

to the required standard.

(g) Disposal of solid waste.

(h) Flood risk to, and/or caused by, the proposed works.

7. Water supply:(a) NWSC offices and their regulations.(b) Locations, sizes and depths of mains.

(c) Pressure characteristics of mains.

(d) Water analyses.

(e) Availability of water for additional requirements.

(f) Storage requirements.

(g) Water sources for fire fighting.

(h) Charges for connections and water.

(i) Possible additional sources of water.

(j) Water rights and responsibilities.

8. Electricity supply:(a) Umeme,UETCL, and regulations;(b) Locations, sizes and depths of mains.

(c) The voltage, phases and frequency.

(d) Capacity to supply additional requirements.

(e) Transformer requirements.

(f) Charges for installation and current.

9. Telecommunications:(a) Local office addresses;

(b) Locations of existing lines;

(c) Charges for installation.

(d) Proposed lines such as underground fibre optic cables.

10.Information relating to potential contamination:(a) History of the site including details of owners, occupiers and users, and of any incidents or

accidents relating to the dispersal of contaminants;

(b) Processes used, including their locations;

(c) Nature and volumes of raw materials, products, and waste residues;

(d) Waste disposal activities and methods of handling waste;

(e) Layout of the site above and below ground at each stage of development, including roadways,

storage areas, hard-cover areas, and the presence of any existing structures and services;

(f) The presence of any waste disposal tips, abandoned pits and quarries


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(g) The presence of nearby sources of contamination from which contaminants could migrate via air

and/or groundwater onto the site.

3bThe preliminary location survey is a large-scale study of one or more feasible routes within a

corridor, each typically 40240 m wide, which is made for the purpose of collecting all physical

information that may affect the location of the proposed roadway.

Many considerations influence the location of the centreline that is finally selected. They include:

(1) In rural locales, locate the road along property edges rather than through themand maximize the

use of existing right-of-ways (to minimize the loss of farmland and the need for subways for crossing

animals and farm machinery).

(2) Avoidalignments that result in the motorist driving into the rising(morning) or setting (evening) sun

for long periodsand, to relieve the monotony of driving on long straight sections, site the road so as to

view a prominent scenic feature.

(3) Minimize the destruction of man-madeculture or wooded areas, and avoid cemeteries, places of

worship, hospitals, old peoples homes, schools and playgrounds.

(4) Avoid highly-developed, expensive, land areasand seek alignments that cause the least amount ofenvironmental (visual and audio) blight.

(5) In hilly terrain, maximize low-cost opportunities to provide long overtaking sections (for single

carriageways) and of using varying central reservation widths and separate horizontal and vertical

alignments (for dual carriageways).

(6) In hilly country also, avoid alignments that are shielded from the sun (so that rainwater on the

carriageway can dissipate).

(7) If avertical curve is imposed on a horizontal curve, ensure that the horizontal curve is longer;

(8) Avoid introducing a sharp horizontal curve at or close to the top of a pronounced crest vertical curve

or the low point of a pronounced sag vertical curve, and make horizontal and vertical curves as flat as

possible at junctions with other roads (for safety reasons).

(9) Seek favourable sites for river crossings(preferably at right angles to stream centrelines), and avoidlocating bridges or tunnels on or near curves.

(10) Minimizethe use of alignments that require (expensive) rock excavation.

(11) Try to ensure that excavation quantities are in balance with embankment quantities (so that

earthworks haulage is minimized).

3(c)

i. Societal benefitsThe highway network of a country forms the backbone of its economy and represents a huge

investment in millions of dollars that allows for the safe and efficient movement of people and goods. A

route with wider effects on the economic development of a region is more likely to be chosen.

These societal beneficial effects may be in the form of direct employment during construction and

maintenance, improved trade and market growth around the areas served by the road and wideraccessibility to services and goods.

ii. Road user costOne of the principal benefits of transport project proposals is the anticipated reduction in travel

time. The final route should achieve maximum time savings by avoiding bottlenecks and providing the

shortest route possible.


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A reduction in accidentsreduces the costs of vehicle repair associated with minor crashes and the

immeasurable cost of human life lost in fatal crashes thus offering a direct benefit to the final road user.

A route with minimum likelihood to cause accidents is likely to be chosen. A safer alignment may be

achieved by the employment of gradual changes in alignment and sufficient traffic signs.

Another direct benefit to the road user is in the form of reduced vehicle operation costs. This may

be achieved by;

offering a better riding surface that reduces vehicle maintenance regularity, a straighter more direct alignment which reduce fuel costs as compared to longer meandering

routes,

iii. Cost of maintenance of the facilityA major consideration in the analysis of any project is the maintenance and life cycle costs. These costs

include annual expenditures for scheduled upkeep and preventive maintenance to keep a road in

operable condition.

A route with lower anticipated maintenance costs is more likely to be chosen as this is offers a

reduction in costs and hence a benefit to the client.

A reduction in the maintenance costs when upgrading an existing structure can be achieved by

improving drainage slopes and sizes of ditches to reduce the effect of climatic factors as well as careful

selection of materials.

iv. Cost of construction of the facilityAny route that minimises the overall construction cost of the proposed alignment is likely to be chosen.

This can be achieved by selecting the shortest alignment with the least obstacles to the roads path such

as valleys, river crossings e.t.c.


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4(a)

Considerations for drawing up geometric design standards of a country

The road project should meet the set environmental standards. The project should meet the economic standards set by the government or donor group.

The different terrain in the country should be clearly defined to enable proper calculation offeatures such as sight distances.

The road should be clearly classified to enable proper evaluation and planning. The design speed and speed limits to be used should be appropriately defined. It is also important to carefully identify a design vehicle to enable proper design to

accommodate all the other vehicles.

4(b)

Super elevationis the inward tilt or transverse inclination given to the cross section of a carriage way

through out the length of a horizontal curve to reduce the effects of centrifugal forces on a moving

vehicle.

The minimum value for super elevation recommended for drainage is 2.5%.

TRANSVERSE SECTION

The diagrams above shows the attainment of super elevation

In fig a) the camber is intact In fig b) the outer edge is raised by placing fill that are then compacted until the fill is as high as

the centre line.

In fig c) more fill is added and compacted until the required slope of super elevation is attained.


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Figs d), e) and f) show the attainment of super elevation about the outer and inner edge. Herethere are fill, cut and compaction processes to achieve this.

Below is the longitudinal section of super elevation about the centre line

LONGITUDINAL VIEW

4(c)

Transition curve

is a curve whose radius continuously changes along its length. It is used to join twocurves with different radii or a straight to a curve.

It is important to have a transition curve;

To promote passenger comfort as it reduces tendencies of sway and shock. To provide convenient sections for pavement enlargement and super elevation. To improve the general appearance of the road. To reduce tendencies of vehicular skidding.

4(d)

=2.5% Length due to acceleration

Length due to super elevation

The radius is greater than 300m so the width of the carriageway needs widening

Super elevation


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21

Therefore the length is 87.52m

ii

iii

L = 132.39m


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22

5(a)

Vertical alignmentis the arrangement of tangents and curves which compose the longitudinal profile

of the road. It is composed of a series of straight-line gradients connected by curves,

normally parabolic in form.

A vertical curve provides a smooth transition between two tangent grades. There are two types of

vertical curves: crest vertical curves and sag vertical curves.The main aim of vertical alignment is to ensure that a continuously unfolding stretch of the road is

presented to motorists so that their anticipation of directional change and future action is instantaneous

and correct *Rogers, 2003; OFlaherty, 2002+.

DIAGRAM SHOWING VERTICAL CURVES

5(b)

In design of vertical curves the following are considered;

The shape of the vertical curve i.e. it can be circular, elliptical or parabolic and in all cases theratio of length to the radius should not be greater than 0.1.

There should be provision of cross falls to enable run off on the road to drain away. This can beachieved by having a camber sloping from the road centre line or sloping from one side of the

road to the other.

The sight distances should be well established because the length of a curve depends on it. The terrain of the area and hence the gradients to be manipulated to come up with an

economical and environmental friendly curve.

The design speed and speed limits of a given section of the road should be well established.


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23

5(c)

Design vehicleis a selected vehicle with maximum dimensions and operating characteristics which are

used as a basis to establish highway design controls to accommodate other vehicles that will use the sae

highway.

Design speed is the maximum safe speed that can be maintained at a given section of a road while

speed limitis a statutory maximum allowable speed on a road section.

5(d)

Length

Elevation of PVC =Elevation PVI +

Elevation of PVC =59.34 +

Elevation of PVI = Elevation PVI +

Elevation of PVI = 59.34 +

For any elevation

This is the formula for finding reduced level of any point.


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The results of the above formulae are tabulated below;

STATIONING CHORD LENGTH CURVE LENGTH ELEVATIONS

0+533.17 0 0 60.948

0+560.00 6.83 6.83 60.794

0+580.00 20 26.83 60.5310+600.00 20 46.83 60.550

0+617.49 17.49 46.32 60.797

0+620.00 2.51 2.51 60.8870+640.00 20 22.51 61.307

0+660.00 20 42.51 61.849

0+680.00 20 62.51 62.476

0+700.00 20 82.51 63.186

0+720.00 20 102.51 63.9810+735.17 15.17 117.68 64.639

In conclusion And its elevation is 64.639m which tally with the results above


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6(a)

Road reserve:

This is the width of land secured and preserved in public interest for road development purposes. It

should be adequate to accommodate all the elements that make up the cross section of the highway

and may reasonably provide for future development.

The width of the road reserve is measured at right angles to the centerline of the road and varies

according to the classification of the road.

Carriage way:

This is the section of the pavement which covers the traffic lanes, any auxiliary lanes and shoulders. Its

width governs the safety and convenience of traffic and has a profound influence on the road capacity.

The factors that influence capacity of a carriageway are:

a) The design volume, i.e. the greater the traffic volume the wider the carriageway and

Normally, the greater the number of lanes;

b) Vehicle dimensions, i.e. heavy commercial vehicles require wider carriageways to ensure

Adequate clearances when passing each other;

c) The design speeds, i.e. vehicles travelling at high speed, especially commercial vehicles, require wider

carriageways to ensure safe clearances between passing vehicles;

d) The road classification, i.e. the higher the road classification the greater the level of service (andwidth of carriageway) expected.

Central reservation/ median strip:

This the longitudinal space separating dual carriages to separate the opposing traffic stream, minimize

headlight glare, provide stopping area in case of emergency and to include space for safe operation of

crossing and turning vehicles at intersections at grade. The width should be adequate for giving working

space around a stopped vehicle.

The central reservations on high-speed heavily trafficked rural roads in the United States are typically

15m to 30m. In Europe they tend to be much narrower (say 4 10m) and to be used with safety

barriers. In urban areas they can be as narrow as 1m, but 3m is preferred so that a crossing pedestrian

pushing a pram or wheelchair has space to wait in safety *OFlaherty, 2002+. On severely restrictedarterial streets, where a narrow separator of 0.6 1.2m is feasible, it may be desirable to have few, if

any, openings in median except at intersections.

Shoulders:

Paved or unpaved width of the road between the edge of the carriageway and the shoulder break point.

The shoulder provides side support for the pavement or gravel surface and allows vehicles to stop or

pass in an emergency .The width of the shoulder should be adequate for giving working space around a

stopped vehicle. American practice recommends a 3m width for high type facility and a width of 1.2m -

2.4m for low type facilities. UK practice for rural roads recommends widths ranging from 1.2m to 3.65m

depending upon the road type and nature of kerb treatment.

.

(a) Camber

Camber, also known as cross fall, is designed to reduce or eliminate the accumulation of water ponding

on the pavement surface; if the water thickness is too great for the tire to make contact with the

pavement surface, hydroplaning can occur where the tire is effectively sliding along a water surface with

almost no ability to generate frictional resistance.

The pavement can have a crown or a high point in the middle with slopes downwards towards

both edges. This is favoured on two-lane roads and wider undivided roads. On divided roads, the


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individual carriageways may be centrally crowned separately or a unidirectional slope may be provided

across the entire carriageway width.

The amount of camber to be provided depends upon the smoothness of the surface and the

intensity of rainfall. In the UK, a value of 2.5% is generally adopted for design. A cross fall for the

shoulders should be generally steeper than for the pavement by about 0.3 0.5% to facilitate quick

drainage. The UK practice is to provide 5% slope on the shoulder [Kadiyali, 2006].

CROSS SECTION TERMS


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27


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28

(b) The preliminary design phase.

The preliminary design phase is essentially an iterative one. It involves preparing a number of possible

intersection layouts and generally examining each in terms of its operating characteristics (especially

safety and capacity), ease of construction and likely capital cost, and environmental and local impacts

that might affect the design selection. The most promising of the rough layouts are then selected for

further development and analysis (including road user and vehicle operating costs, if appropriate),

refined and examined in greater detail until that considered most suitable for the intersection is

selected for detailed design and preparation of final construction plans and specifications *OFlaherty,

2002].

(c)

Summary of design data

W =9m

WCR =8mWB-A=4m

WB-C =4m

WC-B =6m

VrB-A =70m

VlB-A =85m

VrB-C =70m

VrC-B =70m

qA-C=750pcu/hrqC-A=800pcu/hr

qA-B=350pcu/hr

qB-A=100pcu/hr

qB-C=300pcu/hr

qC-B=400pcu/hr

(i) Capacities of turning movements

qsB-A =D{627+14WCRY(0.364 qA-C+0.114 qA-B+0.229 qC-A+0.520 qC-B)} ..(i)

qsB-C =E{745-Y[0.364 qA-C+0.144 qA-B+} (ii)

qsC-B =F{745-0.364Y [qA-C+qA-B]} .(iii)


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Where;

Y=[1-0.0345W]

=[1-0.0345X9]

=0.6895

D = [1+ 0.094(WB-A - 3.65)][1+ 0.0009(VrB-A -120)][1+0.006 VlB-A -150)]

= [1+ 0.094(4- 3.65)][1+0.0009(70-120)][1+0.006 (85) -150)]

= 0.1076

E = [1+ 0.094(WB-C -3.65)][1+ 0.0009(VrB-C-120)]

= [1 + 0.094(4 - 3.65)][1+ 0.0009(70 -120)]

=0.9864

F=[1+0.094(WC-B -3.65)][1+ 0.0009(VrC-B-120)]

=[1+0.094(6-3.65)][1+ 0.0009(70 -120)]

=1.1660

Substituting these values in equations (i), (ii), (iii)


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qsB-A =0.1076{627+14(8)- 0.6895(0.364x750 + 0.114x350 + 0.229x800 + 0.520400)} =27pcu/hrB-C=0.9864{745 - 0.6895[0.364x750 + 0.144x350]}

=515 pcu/hr

qsC-B =1.1660{745 - 0.364x0.6895 [750 +350]}=547pcu/hr

(ii) Assessment of junction arms

Using design reference flow (DRF) to capacity ratio called RFC i.e. Reference to Flow Capacityratio.Arm B-A =DRFB-A = 190 = 7.04 > 0.85 capacity is exceeded

RFC qsB-A 27

Arm B-C =DRFB-C = 300 = 0.58 < 0.85 arm has sufficient capacity

RFC qsB-C 5I5

Arm C-B =DRFC-B = 400 = 0.73< 0.85 arm has sufficient capacity

RFC qsC-B 547

Based on the reference flow capacity ratios obtained, arm B-A has exceeded its capacity and needs

to be redesigned.(iii) Potential junction improvement to accommodate design year flow.

.

Create auxiliary loads to accommodate waiting vehicles. Given sufficient space requirements, the junction can be upgraded to a round-about or

signalized inter section.

Increasing the average width of the road carriageway. Reducing the average width of each of the minor road lanes


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Number 7

a) Characteristics that render roundabouts most effective at grade intersectionsRoundabouts are most effective as at grade intersections that have the following characteristics in

rural or urban areas

High portions and volumes of right turning traffic and with five or more intersecting legs.This is due to the fact that right turning traffic causes difficulty with signal controls when

their numbers are large, therefore making roundabouts more effective in this area

Priority is not given to traffic from any particular road. This occurs when intersecting roadscarry nearly equal amounts of traffic, or where the intersecting roads are both of high

standard and are intersecting at approximately right angles

Presence of accidents involving crossing or turning movements. Junctions that haveconsiderable accident threats call for the use of roundabouts, as it has been observed that

about of accidents occurring at signalized junctions occur at roundabouts. Roundaboutsalso reduce the possible areas of conflicts at junctions, therefore minimizing the possibility

of accidents

Traffic on minor roads is delayed by stop or give way signs Where they cause less overall delay to vehicles. This is achieved by eliminating the necessity

of stopping the crossing streams of vehicles

Where there is a marked change in road standard for example, when one is moving from asingle to a dual carriage road

b) Design features of roundaboutso For small roundabouts, the central island should be approximately of the inscribed circle

diameter

o The circulatory width around the roundabout should be constant at about 1.0 to 1.2 timesthe highest entry width subject to a maximum of15 meters

o Entries should be flares. Single and two lane approaches should become 3 and four lanesrespectively at give way lines

o Steep downhill gradients should be avoided at round about approacheso Pedestrian guard rails should be used to control haphazard pedestrian crossing of traffic

streams and to provide safety

o The range of suggested parameters for the design of roundabouts are given in the tablebelow

Table 7a

Symbol Description Recommended range for design

e Entry width 4.015.0m

v Approach half width 2.07.3m

l Average effective flare length 1.0100.0 m

S Sharpness of flare

D Inscribed circle diameter 15100m

Entry angle 10 - 60

r Entry radius 6.0100.0m


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c) Given dataTable 7(b)

Geometric parameter symbol unit Arm C Arm D

Entry width e m 7.0 12.0

Approach half width v m 3.5 5.5Average effective flare

length

l m 50.0 50.0

Sharpness of flare S

Inscribed circle diameter D m 40.0 40.0

Entry angle deg 35.0 30.0

Entry radius r m 50.0 50.0

Table 7 (c)

To (Destination)

From

(origin)

A B C D

A 20 160 230 100

B 140 0 205 160

C 220 190 8 210

D 150 180 170 12

Facility to be opened to traffic in 2007

Design year 2026

Traffic growth rate r = 8%

Geometric parameters of arms C and D are shown in the table 7 (a)

Design life Y = (2026-2007) +1

=20 years

I. Design flows (DF) for the year 2026 were obtained by multiplying the values intable 7 (b) by theequation

DF = 1.125P (1+r)y

Where P present flows in table 7(b) in pcu/hr

Y design life (20 years)

r traffic growth rate

Multiplication produced these values in table 7(c) below

Table 7(d)

To (Destination)

From

(origin)

A B C D

A 105 839 1206 525

B 735 0 1075 839

C 1154 996 42 1101

D 787 944 891 63


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II. Entry capacity for arms C and D, Qe= K(F - feQc)Where K = 1-0.00347( -30)0.978[(

F = 303X2, where X2= v + and S=

fc = 0.21tD(1+0.2x2), where tD= 1+ 0.5/(1+M) and M=exp[(D-60)/10]

Arm C

K = 1 - 0.00347( -30)0.978[( = 10.00347(3530)0.978[( = 1.01199

F = 303X2, where X2= v + and S =

S =

= 0.112

X2 = 3.5 + [

= 6.3596

F = 303 = 1926.93


M = e([40-60)/10)

= 0.1353

tD = 1 + 0.5/(1+0.1353)

= 1.4404

fc = 0.21 = 0.687

Approach capacity, Q = QCA+ QCB+ QCC+ QCD

= 1154 + 996 + 42 + 1101

= 3293

Circulating capacity Qc = QAA+ QBB+ QDD+ QBA+ QBD+ QAD

= 105 + 0 + 63 + 735 + 525 + 839

= 2267

Entry capacity Qe = K(F - feQc)

= 1.01199 (1926.93(0.687= 373.93

Arm D

K = 1 - 0.00347( -30)0.978[( = 10.00347(3030)0.978[( )0.05]= 1.02934


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34

F = 303X2, where X2= v + and S=

S =

= 0.208

X2 = 5.5 +

= 10.0904

F = 303= 3057.39


M = e([40-60)/10)

= 0.1353

tD = 1 + 0.5/(1+0.1353)

= 1.4404

fc = 0.21 ( )= 0.913

Approach capacity Q = QDA+ QDB+ QDC+ QDD=787 + 944 + 891 +63

=2685

Circulating capacity Qc = QAA+ QBB+ QCC+ QCA+ QCB+ QBA= 105 + 0 + 42 + 1154 + 996 + 735

= 3032

Entry capacity Qe = K (F - feQc)

= 1.02934 (3057.39(0.913 = 297.66

III. Checking which of the arms still has capacity

For sufficient capacity, RFC =

Arm C, RFC =

= 8.806

Arm D, RFC =

= 9.02

Since RFCc 8.806, and RFCD=9.02 are far greater than the upper limit of 0.85, queuing will

occur during peak hours on these arms of the roundabout


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(8a)

Disruptions due to maintenance. Traffic disruption due to maintenance last longer on rigidpavements than on flexible pavements.

Riding characteristics. Due to increased variability in ground conditions, rigid pavementstend to offer a better riding surface than a flexible pavement.

Ease and cost of repair. The cost and repair of flexible pavements is cheaper as comparedto rigid pavements.

Effect of climatic conditions. Flexible pavements are more susceptible to climatic effectsthan rigid pavements.

Life time costs. The life time costs incurred in flexible pavements are high due to frequentmaintenance. In rigid pavements, the initial capital investment is higher.

Noise pollution. Bituminous surfacingsare traditionally considered to be quieterand arepreferred for use in locales where noise is deemed a problem.

Construction time. Flexible pavements can be opened to traffic as soon as compaction iscompleted and the surfacings have cooled to the ambient temperature, whereas rigid ones

formed from conventional mixes cannot be opened until they have gained sufficient

strength.

Variation in loading. Concrete pavements are generally better able to cope withunexpected loads and fuel spillagesin industrial estates and service areas. For example, if a

new housing or industrial estate is being built and it is a requirement that the roads be

constructed first so that they can be used by both construction traffic and subsequent

general traffic, concrete is considered by many to have a clear advantage.

8b

The structure of a road pavement is composed of superimposed layers of selected and processed

materials that are placed on the basement soil or subgrade.

The main structural function of a pavement is to support the wheel loads applied to the carriageway

and distribute them to the underlying subgrade.

SURFACING

The uppermost layer of a flexible pavement is called the surfacing. The primary function of this layer

is to provide a safe, smooth, stable riding surface, i.e. a carriageway, for traffic; its secondaryfunctions are to contribute to the structural stability of the pavement and protect it from the natural


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elements. The majority of modern-day surfacings in the western world are bitumen-bound; only

minor road surfacings are now composed of soilaggregate materials. When a surfacing is composed

of bituminous materials it may comprise a single homogeneous layer or course; more usually,

however, with heavily-trafficked roads, two distinct sublayers known as a wearing course and a

basecourse are laid in separate operations.

The wearing course forms the uniform carriageway surface upon which vehicles run. Ideally, itshould;

(i) offer good skid resistance,(ii) allow for the rapid drainage of surface water,(iii) minimize traffic noise,(iv) resist cracking and rutting,(v) withstand traffic turning and braking forces,(vi) protect the underlying road structure,(vii) require minimal maintenance,(viii) be capable of being recycled or overlaid,(ix) be durable and give value for money.No one material meets all of these requirements so, in practice, the selection of a wearing coursematerial depends on the design needs at each site.

The basecourse (also called a binder course) is a structural platform which regulates (i.e. makes

even) the top of the underlying roadbase, thereby ensuring that the wearing course has a good

riding quality when built; it also helps to distribute the applied traffic loads. If the wearing course is

impervious, the basecourse can be composed of a more permeable material.

The roadbase, which provides the platform for the surfacing, is the main structural layer in a

flexible pavement. As the stresses induced in a flexible pavement by the applied wheel loads

decrease with depth, the main function of the roadbase is to distribute the loads transmitted to it so

that the strength capacities of the weaker subbase and subgrade are not exceeded. Roadbases in

flexible pavements are normally designed to be very dense and highly stable, and to resist fatiguecracking and structural deformation. If a pavement is formed with layers of bitumen- and cement-

bound materials, the structure is often referred to as a composite pavement. The rationale for

building a composite pavement is to combine the better qualities of both flexible and rigid

pavements. In the UK, a flexible composite pavement is defined as having its surfacing and upper

roadbase (if used) constructed from bituminous materials, supported on a roadbase or lower

roadbase of cement-bound material.

The material for the base course is typically unstabilized aggregates.

A subbase is very often present in a flexible pavement as a separate layer beneath the roadbase.

Whether it is present, or how it is used, depends upon its intended function(s). As a structural layer

within the pavement the subbase further distributes the applied wheel loads to the weakersubgrade below.

Whilst the subbase material is of a lesser quality (and, thus, is normally cheaper) than the

roadbase material, it must be able to resist the stresses transmitted to it via the roadbase and it

must always be stronger than the subgrade soil.

Another major function of the subbase is to act as a working platform for, and protect the

subgrade from, site and construction vehicles as a pavement is being built. This is especially

important when the subgrade is of poor quality, e.g. clayey or silty, as the critical load-carrying

period is when the heavy wheel loads used in the laying and compaction of the roadbase are applied

to the subbase during construction.

The subbase is mostly a local aggregate material.


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(8c)

Summary of design information

Number of wet months, Number of dry months, Subgrade CBR, Traffic growth rate varies with vehicle classDesign PERIOD 20 years

Construction materials

Surfacing material asphalt concrete

Roadbase crushed stone

Subbase Natural gravel

Subgrade good quality gravel

Determination of subgrade strength, S

From table 5.1, the CBR range given as 13-15% falls in the range of 12-20% corresponding to

subgrade class of S3

Determination of cumulative design traffic

Unidirectional flow, V

Assuming a maximum directional split of 2:1 for two way traffic of the traffic volume or each class VEHICLE

CLASSTOTAL TRAFFIC

FLOWUNIDIRECTIONAL

TRAFFIC FLOW, V0GROWTH

RATE(%)PROJECTED

FLOW, VP

MINI BUSES 2511 1682 7 2524BUSES 322 216 5.5 298

PICKUPS 588 394 2.5 457

2 AXLE

TRUCKS 495 332 5.7 463

3 AXLE

TRUCKS 131 88 4.5 115

WEAR FACTOR, C

VEHICLE

CLASSGROSS

WEIGHT FRONT AXLEREAR AXLE

1REAR AXLE

2WEAR FACTOR,

C

MINI BUSES 29.43 9.81 19.62 0 0.0038

BUSES 147.15 29.43 58.86 58.86 0.6044

PICKUPS 29.43 9.81 19.62 0 0.0038

2 AXLE

TRUCKS 117.72 39.24 78.48 0 0.9840

3 AXLE

TRUCKS 196.2 39.24 78.48 78.48 1.9102


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38

GROWTH FACTOR

]

VEHICLE CLASS ANNUAL GROWTH RATE, r (%) GROWTH FACTOR, G

MINI BUSES 7.0 2.0498

BUSES 5.5 1.7434

PICKUPS 2.5 1.2772

2 AXLE TRUCKS 5.7 1.7811

3 AXLE TRUCKS 4.5 1.5686

FINAL COMPUTATIONS FOR DT

VEHICLE CLASS v C G Ti

MINI BUSES 2524 0.0038 2.0498 0.1435

BUSES 298 0.6044 1.7434 2.2909

PICKUPS 457 0.0038 1.2772 0.0162

2 AXLE TRUCKS 463 0.984 1.7811 5.9237

3 AXLE TRUCKS 115 1.9102 1.5686 2.5067

DT=10.8810

From table 5.4, our cumulative design traffic of 10.8810 falls in the range of 8-20 msa which

corresponds to a traffic class of T1.

Required design structural number, DSN

* +

Using chart number 2 with a subbase of natural gravel and a base of crushed stone, the following

parameters are obtained; ,

* +

Layer thickness based on actual Design strength number, DSN

From design chart number 2, for a subgrade strength class of S3, and traffic class of T1, the

corresponding asphalt thickness, h1is 80mm, and from table 5.6, the layer coefficients are; The pavement should therefore be composed of;

1. Surfacing material : 80mm2. Roadbase : 175mm3. Subbase : 250mm


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References

1. Okello, F.E. (2010). Lecture Notes for CE323 Highway Engineering I, Kyambogo University.Kampala:

2. OFlaherty, C.A. (2002). Highways: The Location, Design, Construction and Maintenance ofRoad Pavements(4thEd.). Oxford, Butterworth-Heinemann.

3. Brokenbrough, R.L. (2009). Highway Engineering Handbook (3rd ed.). United States ofAmerica: McGraw-Hill.

4. Ministry of Works, Housing and Communications, Uganda. (2004). District Road Works,Volume 1 - Technical Manuals: Manual A: Technical Manual. Uganda: Ministry of Works,

Housing and Communications.

5. United Kingdom, Department of Transport, Overseas Development Administration, TRRLOverseas Unit. (1988). ORN 5: A Guide to Road Project Appraisal. Berkshire: TRL

International.

6. Salvatore, D., & Diulio, E. (2003). Schaums Easy Outline: Principles of Economics. UnitedStates of America: McGraw-Hill.

7. Garrabrant, R., (2004). Highway Engineering. United States of America: McGraw-Hill.8. Mathew, T.V., (2006). Lecture Notes for Transportation Engineering I, Indian Institute of

Technology Bombay. Mumbai:

9. Transport. (2009). Wikipedia. Retrieved April 10, 2009 fromhttp://en.m.www.wikipedia.org/wiki/Transport.html

10.Microsoft Student with Encarta Premium 2008 [DVD]. Redmond, WA: Microsoft Corporation.11.R.J.Slater, Highway Traffic Analysis and Design12.Dr. L.R. Kadiyali, Principles and practices of Highway Engineering13.T.F. Fwa, (2006). The handbook of highway engineering. Taylor and Francis group
http://en.m.www.wikipedia.org/wiki/Transport.htmlhttp://en.m.www.wikipedia.org/wiki/Transport.htmlhttp://en.m.www.wikipedia.org/wiki/Transport.html

final highway copy

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