EXPLORATION OF SAFETY PERFORMANCE AND TRAFFIC BEHAVIOUR ON

SELANGOR-KUALA LUMPUR URBAN EXPRESSWAY AT MERGING SECTION

INSTITUT PENYELIDIKAN, PEMBANGUNAN DAN PENGKOMERSILAN (IRDC)

UNIVERSITI TEKNOLOGI MARA 40450 SHAH ALAM, SELANGOR

MALAYSIA

DISEDIAKAN OLEH

MUHAMMAD AKRAM ADNAN ANAS IBRAHIM

JOE DAVYLYN NGUIN NORLIANA SULAIMAN

FEBRUARI 2006

COPYRIGHT UiTM

Tarikh : 1 Februari 2006 No. Fail Projek 600-IRDC/ST.5/3/750

Penolong Naib Canselor (Penyelidikan) Institut Penyelidikan, Pembangunan dan Pengkomersilan (IRDC) Universiti Teknologi MARA 40450 Shah Alam SELANGOR D. EHSAN

Y.Bhg. Prof.,

LAPORAN AKHIR PENYELIDIKAN "EXPLORATION OF SAFETY PERFORMANCE AND TRAFFIC BEHAVIOUR ON SELANGOR-KUALA LUMPUR URBAN EXPRESSWAY AT MERGING SECTION"

Merujuk kepada perkara diatas, bersama-sama ini diserakan dua (2) naskah Laporan Akhir Penyelidikan bertajuk "EXPLORATION OF SAFETY PERFORMANCE AND TRAFFIC BEHAVIOUR ON SELANGOR-KUALA LUMPUR URBAN EXPRESSWAY AT MERGING SECTION" oleh kumpulan Penyelidik berkenaan dari Fakulti Kejuruteraan Awam (FKA), Universiti Teknologi MARA (UiTM), Shah Alam, untuk makluman pihak Y.Bhg. Prof.

Sekian terima kasih.

Yang benar,

MUHAMMAD AKRAM ADNAN Ketua Projek Penyelidikan

ii COPYRIGHT UiTM

Surat Kami : Tarikh :

600-IRDC/ST.5/3/750 9 Julai 2004 C lOW l>)

Encik Mohd Halil Marsuki Penolong Akauntan Unit Kewangan Zon 17 Universiti Teknologi MARA Shah A lam

UNIVERSITI TEKNOLOGI MARA Institut Penyelidikan, Pembangunan dan Pengkomersilan (IRDC) Institute of Research, Development and Commercialisation (IRDC) (Sdbehtm ini dikcmdi sdmgai Biro Pemjelidikau dan Perumthtgait) 40450 Shah Alam, Malaysia Website : http/ /: www.uitm.edu.my/brc

Tuan

GERAN PENYELIDIKAN

Merujuk kepada perkara di atas, bersama-sama ini dimajukan salinan surat kelulusan menjalankan penyelidikan untuk pensyarah dari Universiti Teknologi MARA Cawangan Pulau Pinang;

1. Road safety implication of residence in rural area : A case study Ketua Projek Kos Projek Jen is Geran

En. Muhammad Akram Adnan RM 20,000.00 Geran Dalaman

Diharapkan tuan dapat menghantarkan geran penyelidikan ke Universiti Teknologi MARA Cawangan Pulau Pinang.

Terimakasih.

PROF.MADYA" tuaPenye

/ DR MANSUR AHMAD

lidikan (Sains dan Teknologi) b/p Penolong Naib Canselor (Penyelidikan)

s.k: Pengarah Kampus Universiti Teknologi MARA Cawangan Pulau Pinang

Prof Madya Peridah Bahari {Coordinator URDC Universiti Teknologi MARA Cawangan Pulau Pinang

Penolong Bendahari Universiti Teknologi MARA Cawangan Pulau Pinang

En. Muhammad Akram Adnan Ketua Projek

?ENYELIDIKAN, PEMBANGUNAN DAN PENGKOMERSILAN LANDASAN KEWIBAWAAN DAN KECEMERLANGAN

! Naib Canselor (Penyelidikan) nyelidikan (Sains Sosial d

PENGHARGAAN

Setinggi-tinggi penghargaan dan ribuan terima kasih diucapkan kepada semua pihak yang terlibat secara langsung bagi membolehkan projek penyelidikan ini disiapkan

dengan sempurna

Di antaranya

Prof. Madya Ir. Hj. Mohd. Yusof Abdul Rahman (Dekan Fakulti Kejuruteraan Awam)

Penolong Naib Canselor (Penyelidikan) dan anggota kerja (IRDC, UiTM, ShahAlam)

Tengku Mohd Fadzil (Pembantu penyelidik)

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KUMPULAN PENYELIDIK

MUHAMMAD AKRAM ADNAN KETUA PROJEK

II Tarjdatangan

ANAS IBRAHIM AHLI

Tandatangan

JOE DAVYLYN NGUIN AHLI

cjac. Tandatangan

NORLIANA SULAIMAN AHLI

IV

COPYRIGHT UiTM

TABLE OF CONTENTS

ACKNOWLEDGEMENT TABLE OF CONTENTS LISTS OF TABLES LISTS OF FIGURES ABSTRACT

CHAPTER ONE 1.0 1.1 1.2 1.3

INTRODUCTION General Introduction Objectives of Study Significance of Project Scope of Study

CHAPTER TWO 2.0 2.1

2.2 2.3 2.4 2.5 2.6

2.7 2.8 2.9 2.10

LITERATURE REVIEW General Introduction Interchange Design Criteria

Ramp Terminal Spacing Ramp Speed and Width Speed Change Lanes Lane Balance at Merge and Diverge Areas Operational Characteristics at Expressway Ramps Capacity of Merge and Diverge Area Level of Service (LOS) Driver Behavior at Ramp Car Following Model

CHAPTER THREE METHODOLOGY

CHAPTER FOUR

4.1

4.2

4.3

4.4 4.5 4.6

4.7

RESULTS Site 1: Speed Differential Ramp Vehicle and Lead Vehicle Site 2: Speed Differential Ramp Vehicle and Lead Vehicle Site 3: Speed Differential Ramp Vehicle and Lead Vehicle Site 4: Speed Differential Ramp Vehicle and Lead Vehicle Time Merge Data for Four(4) Sites Data Reduction for VI,VF, VR, Vol/Du and LA Data Reduction for Tm, VI, VR, LA andVF

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CHAPTER FIVE DISCUSSION 5.1 Demand management 5.2 Supply Management 5.3 Ramp Junctions On Expressway 5.4 Entrance Ramp Junction Design 5.5 Model Development

CONCLUSIONS REFERENCES APPENDIX A

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LIST OF TABLES

TABLES DESCRIPTION PAGE

2.1 Ramp Design Speed Domain 7 2.2 Class of Level of Service and the condition 17 2.3 Limiting Volumes in Passenger Cars per hour for 18

freeway 5.1 Level of Service Criteria for Merge Area 51

LIST OF FIGURES

FIGURES

2.1 2.2 2.3 2.4 2.5

4.1

4.2

4.3

4.4 4.5

5.2

DESCRIPTION

Consistency of Exits Acceleration and deceleration lane of Ramp Ramps Junction Methodology Ramp Configuration Illustration of Vehicles Merging Process at on-ramp for several traps Ramp Vehicle Speed vs Expressway Lead vehicle speed for site 1 and 2 Lead Vehicle Speed differential vs Ramp vehicle speed for site 1 and 2 Ramp Vehicle Speed vs Length of Acceleration lane for all sites Average merging time vs ramp flowrate for all sites Flowrate lane 1 vs acceleration lane length for all sites Level of Service Criteria for Merge Area

PAGE

6 11 13 19 24

44

45

46

46 47

51

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ABSTRACT

As defined in the Highway Capacity Manual (HCM 2000), an expressway is a divided highway with full control of access and with two or more lanes for each direction. The two directions of the expressway must be completely separated along its entire length. Accesses to expressways are only allowed at entrance ramp and expressways vehicles exit through off- ramp. From the view point of a highway and traffic engineer, there are two types of ramp. On ramp or entrance ramp, by which drivers can enter the expressway and off-ramp or exit ramp by which drivers can leave the expressway. This research explores the safety issues during the maneuverability during merging and diverging operation. During the process of merging, ramp vehicles need to adjust their speed and gaps in order to enter mainline safely. Expressway areas at entrance and exit ramps are characterized by concentrated turbulence to the traffic stream on the mainline due to intensive vehicular interaction. Therefore, these areas, which include ramp merge, diverge and weaving section are viewed as potential bottlenecks in expressway operations. Acceleration and deceleration lanes are designed as safety facilities allowing ramp vehicles to make a smooth merge without causing interference to expressway

streams. A well designed acceleration lane should permit drivers to perform a safe merge as well as deceleration lane for smooth diverging process. The knowledge of operational performance at these critical areas is importance to various

transportation applications including planning, design, operation and management. At present, there are no adequate procedures that can be used to consider the impacts of traffic conditions or geometric features on expressway traffic performance and safety based on Malaysian expressway conditions. Due to the lack of guidance in the current practice, this research attempts to describe an overview understanding and set up the basis of expressway operational performance and safety behaviors at these critical areas for practical consideration for Malaysian practice. A model have been developed for ramp merging process and systematic methodology to evaluate the safety operational performance had been proposed for Malaysian driving style.

Keywords: Expressway, Merging process, Safety issues and Microscopic analysis.

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1. GENERAL INTRODUCTION

According to the highway design classification system, roads have been traditionally been

classified into four groups; locals, collectors, arterials and expressway. Each group can

provide a different level of the two fundamental functions of mobility and accessibility. Since

expressway are more associated with high speeds, which the main function is to provide high

mobility , a collision on expressway will be more likely to cause a fatality and a serious

injury.

There are many factors affecting safety performance on expressway. This research explores

the safety issues within merge and diverge areas on expressway system. The safety

performance such as distance available for acceleration lane and deceleration lane play a

major role in merging and diverging process. Therefore, dynamics traffic stream performance

depends on driver behaviors, vehicle capabilities and facilities design. Operation at merge

junction area is a complex pattern of driver behaviors. Ramp drivers need to perform several

tasks during the merging process from acceleration lane to enter lane 1 mainline streams.

1.1 O bj ectives of Study

The objectives of this research were set as follows:

Summarizing the available literature on factors contributing to safety performance on

Malaysia Urban Expressway Systems.

Reviewing the previous research on safety performance of the merge and diverge

areas.

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Estimating the expected safety improvements and collision reduction using modeling

techniques.

Development of flowrate model in merge influence area.

1.2 Significance of Project

This study aimed to provide an in depth understanding of the influence phenomenon and the

merging characteristics of expressway entry process based on field observations, so that

innovative methods and procedures can be developed for promoting adequate design and

efficient operations of expressway entrance facilities, and for identifying the safety issues in

ramp expressway turbulence areas.

1.3 Scope of Study

In urban areas, the types of expressway vary according to different sites. Due to the variety of

the geometric layout, it is impossible to handle all types of expressway on- ramp research.

With regards to an affordable effort, this research is focused on six lanes expressway on

ramps with a limited set of geometric and operational conditions. Only parallel type

acceleration lanes were considered and the acceleration lane length range from 150m up to

240m.

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2. LITERATURE REVIEW

This chapter provides some of the design criteria and definitions that were mentioned in the

current design guidelines such as the Manual for Interchange Design Arahan Teknik Jalan,

(JKR,1986), the Transportation Association of Canada (TAC 1999), the Highway Capacity

Manual (HCM 2000), and the American Association of state Highway and Transportation

Officials (AASHTO 2001).

2.1 INTERCHANGE DESIGN CRITERIA

An interchange is defined in Arahan Teknik Jalan- Interchange Design (1986) as a

system of interconnecting roadway in conjunction with one or more grade separations that

provides for the movement of traffic between two or more roads and for any range of design

speeds. The main difference between an interchange and a simple at grade intersection is that

the first permits high traffic volumes with relatively safer operations and smooth

maneuvers. Typically, interchanges eliminate crossing conflicts and minimize turning

conflict between traffic volumes for different movement directions.

It is highly recommended in TAC (1999) to consider a consistent design for a series of

interchanges in conjunction with individual interchange design. This supports the important

relationship between the design consistencies of different roadway elements and safety.

In general, reliable, specific and explicit quantitative correlations between interchanges

parameters and safety are not available (TAC 1999). However, the interest in explaining the

explicit relationship between design criteria and safety has recently become an attractive

point in transportation fields as was found in the recent research.

The location of the interchanges along any expressway should be selected based on two

criteria. The first criterion is to provide an adequate service that is needed by the surrounding

communities along the Expressway. This could be interpreted as a need for more interchanges

near business and congested areas. The second criterion is to minimize the disturbance in the

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traffic operation that might result from high density of access points. The balance between

these two criteria would result in acceptable interchange spacing under the prevailing

conditions.

As mentioned in TAC (1999), interchanges are normally located 3 to 8 km apart in rural areas

at which population density is not high. However, in urban areas, this relatively long distance

cannot serve the community in a proper manner. Therefore, a recommendation to use

interchange spacing of 2 to 3 km was mentioned in TAC (1999). Besides, designers need to

note that "Freeway collision rates tend to increase as interchange spacing decreases in urban

areas. This effect on collision rates is an important consideration in urban area interchange

spacing."(TAC 1999, 2.4.3.1)

AASHTO (2001) design guide proposed lower values of interchange spacing than the values

mentioned in TAC (1999). It was recommended in AASHTO (2001) to use a distance of at

least 3 km in rural areas. In addition, this distance is recommended to be 1.5 km in urban

areas. In cases that require a relatively short distance between interchanges than these

minimum values, expressway could be provided with collector distributor roads.

2.2 Ramp Terminal Spacing

The spacing between each two successive ramps along the highway represents one segment.

Ramp terminal spacing could be located between interchanges or within one interchange.

Typically, highway segments can be divided into four main types; namely: (1) entrance-

entrance:, (2) entrance-exit; (3) exit-entrance; and (4) exit-exit. The classification is based

mainly on the type of the first ramp and second ramp for a specific segment. The length of

each segment is stated to be measured from the physical nose at the gore of the first ramp to the

physical nose at the gore of the second ramp. TAC (1999; sets empirical values, for ramp

terminal spacing that are based on different criteria as follow:

1. Distances between an entrance and exit were recommended to be based

on weaving requirements.

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2. Distances between two successive exits should be based on the provision of

adequate signing to enable vehicles to do the required maneuvers

properly.

3. Distances between two successive entrances should be enough for

vehicles joining the freeway from the first entrance to merge safely.

4. Distances between an exit and entrance should be enough for vehicles to

be prepared for the next merge.

Ramp uniformity or consistency has been stressed in the TAC guide, and can be considered a

special application of the general design consistency concept. It was mentioned that, the

consistency between the ramps would guarantee safe and smooth traffic operation on

expressway. Ramp uniformity could be provided through maintaining single exits ahead of

structures on a specific expressway length. Ramps located ahead of underpass structures are

more preferable to be used than ones with exits beyond the structures. They are more visible to

the driver and they help the drivers to select the appropriate speed and adjust the vehicle

position to perform safe maneuvers. Moreover as mentioned in TAC (1999), the left-hand

entrance of the high speed roadways is not a preferable design. On the other hand, using right-

hand side exits is more suitable in terms of consistency and uniformity.

It is obviously indicated that the interchanges have a mix of single and double exits.

In addition, some of the exits are beyond the structure and the rest are before it. This design is

considered inconsistent and would cause a kind of confusion for the driver. On the other hand,

the second design scheme consists of a consistent design in which all interchanges have

single exits before the structure. This kind of consistency would keep the driver concentration

at a uniform level and hence improve operating conditions.

AASHTO (2001) emphasized the same concept in which designing a series of

interchanges should consider the consistency of the interchanges as well as individual

interchange. Expression interchange uniformity was used by AASHTO (2001) to apply the

concept of using consistent exits and entrances. Generally, "Considering the need for high

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capacity, appropriate level of service, and maximum safety in conjunction with freeway

operations, it is desirable to provide uniformity in exit and entrance patterns'XAASHTO

2001, p 811).

inglawlt trudurt

ingtaaxN btfofv ctructin

lngto xlt twfora tnjctum

v$r ^ j y ~^r -* inconsistent exits

all tingle exits Mora structw*

^

consistent exits

Figure 2.1: Consistency of Exits (TAC 1999).

The consistency concept could be one of the main factors that caused this relatively high

collision frequency observed at expressway sections.

2.3 Ramp Speed and Width

For further achievement of the consistency concept along the highway, design speeds for

terminal ramps are recommended to be carefully selected in order to keep the expectancy of

the driver at reasonable values. Table 2.1 shows the recommended design speeds for ramps

with the domain concept as mentioned in TAC (1999). Conceptually, it is desirable to have

ramps with design speeds relatively close to the highway speed. Therefore, the upper limit in

this table is more recommended. For suitable ramp widths, was mentioned in TAC (1999)

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that ranges from 4.8 m to 5.0 m would be sufficient for single ramps. However, for ramps

with two lanes or more, it is recommended to use lanes with a minimum width of 3.7 m.

Table 2.1: Ramp Design Speed Domain, (TAC, 1999)

Roadway Design Speed

(km/h)

Ramp Design Speed Domain

(km/h) 60 70 80 90 100 110 120 130

50-40 60-40 70-40 80-50 90-50 100-60 110-60 110-70

2.4 Speed Change Lanes

Speed change lane is defined in TAC (1999) as an added lane adjoining the traveled way

of the roadway and does not necessarily imply a definite lane of uniform width. It was also

mentioned that speed change lanes should have enough length to guarantee collision-free and

comfortable operation. TAC (1999) stated that the length of a speed change lane is based on

three factors; (1) the running speed on the through lanes; (2) the control speed of the ramp; (3)

the manner of decelerating or accelerating on the speed change lanes.

Typically, there are two main types of speed change lanes; namely: parallel type and direct

taper type. The parallel type is an auxiliary lane that consists of two parts; (1) Ld: that has a

constant width for gradual speed change between the freeway and the ramp and (2): L,: that

has a gradual change in width to guarantee adequate lateral movement rate. On the other

hand, the direct taper type of speed change lanes consists of an auxiliary lane that has a

gradual change in lane width. "This type works on the principle of a direct entry or exit

at aflat angle" (TAC 1999).

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Another definition for the speed change lane was mentioned in AASHTO

(2001) as an auxiliary lane, including tapered area, primarily for acceleration or deceleration

of vehicles entering or leaving the through-traffic lanes. Generally, the purpose of the speed

change lane was stated as: "An auxiliary lane may be provided to comply with the concept

of lane balance, to comply with capacity needs, or to accommodate speed changes,

weaving, and maneuvering of entering and leaving traffic" (AASHTO 2001).

To minimize the disturbance of the through traffic operation, speed change lanes are

recommended to be included in the design especially for highways having expressway

characteristics. A sufficient width and length for speed change lanes are required to facilitate

the traffic maneuvers at the merge and diverge areas in a proper way. In addition, it was

mentioned in AASHTO (2001) that the auxiliary lane should be provided with lane width

equal to the through lane width. Moreover, the shoulder width should be ranged from 2.4

to 3.6 m with minimum of 1.8m (AASHTO 2001). Some considerations regarding speed

change lanes were also mentioned as follow:

Speed change lanes are more reasonable to be used in highways with high

speeds and high volumes.

Some of the drivers use little of the available speed change lanes. However, these

lanes are necessarily to improve traffic operations on highways. Extent of drivers' use

of speed change lanes depends on the traffic volumes.

Using speed change lanes with a long taper fits more the behavior of most

drivers.

Deceleration lanes before off-ramps may function as storage lanes besides the main

function of changing speeds.

In addition, using continuous auxiliary lanes between the entrance and exit ramps are

recommended by AASHTO (2001) in three cases: (1) at interchanges that are close to each

other; (2) when the distance between the end of the taper on the entrance and the beginning of

the taper on the exit terminal is relatively short; (3) when local frontage roads do not exist.

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Moreover, the auxiliary lane could be terminated in two-lane exit, or in single-lane exit.

Another method of terminating the auxiliary lane is to carry the full width auxiliary lane to

the nose before tapering it into the mainline roadway. In case that a single-lane exit

experiences disturbance with vehicles attempting to recover on the through lane, the recovery

lane should be extended 150 to 300 m before being tapered .For large interchanges, designers

might need to extend the auxiliary lane for approximately 750 m downstream the influence of

the interchange.

The merging vehicles coming from the on-ramp initially occupy the acceleration lane and

then seek an acceptable gap to safely join the freeway. This process requires accelerating the

vehicle from a lower speed at the ramp to a higher one on the freeway before reaching the

end of the acceleration lane. The entering vehicles cause other vehicles moving on the

expressway to push themselves away from the lanes adjacent to the on-ramp. On the other

hand, a diverging area is defined as the area at which a single traffic stream splits into two

streams (HCM 2000). Vehicles that separate from the freeway stream first occupy the

deceleration lane and then reduce their speed from the freeway speed to the ramp speed.

Providing adequate length for acceleration and deceleration lanes can give drivers time to

complete their maneuvers safely.

2.5 Lane Balance at Merge and Diverge Areas

The balance between the numbers of lanes is a vital factor that should be considered at any

segment on the freeway. It was mentioned in the Arahan Teknik, Interchange Design,(1986)

as well as the AASHTO (2001) that, at merge areas, the summation of the number of lanes of

the expressway upstream the merge area and the number of lanes of the on-ramp should be

equal to or one more than the number of lanes downstream the merge section. In addition, at

diverge areas; the number of the lanes upstream a diverge area should be less one than the

summation of the number of lanes of the off-ramp and the number of lanes downstream a

diverge area. In cases "Where an auxiliary lane is extended beyond an entrance to maintain

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both lane balance and basic lanes, the lane should be continued for 700 m to 900 m to

permit entering traffic to disperse into the through lanes "..

2.6 Operational Characteristics at Expressway Ramps

A ramp is a length of roadway providing an exclusive connection between two highway

facilities. It measured from the intersection of the edge of the travel way for the expressway

and the ramp, and the downstream intersection of the expressway and ramp edge of the travel

way. On expressway, all entering and exiting maneuvers take place on ramps that are

designed to facilitate smooth merging of on-ramp vehicles into the expressway traffic stream.

Generally, ramp consists of three geometric elements of interest, which are ramp-freeway

junction, the ramp roadway and the ramp-street junction operations are influence by: (HCM,

2000)

Length and type of acceleration or deceleration lanes

free flow speed (FFS - vary between 30km/h to 80 km/hr) or the ramp

immediate vicinity of the junction

sight distance and etc.

Ramps come in various configurations appropriate to the design of the interchange in

which they are located. Many ramp types are named after the interchange types in

which they are most commonly used. Thus, the ramps of a diamond interchange are

typically known as diamond ramps, and the loop ramps within a partial cloverleaf

interchange are typically known as loop ramps. Each of the ramps of the ramp

configurations illustrated serves traffic exiting from a mainline expressway, but an

analogous ramp configuration for traffic entering the mainline expressway also exists.

A ramp that leaves a mainline expressway facility is known as an off-ramp or exit

ramp. A ramp that joins a mainline expressway facility is known as an on-ramp or

entrance ramp. This distinction is important because vehicles typically travel along

off-ramps at higher speeds than along on-ramps, so that accidents are more likely to

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occur on off-ramps. Ramps that join mainline freeways at both ends serve as both off-

ramps and on-ramps. Ramps are connected to mainline freeways and, in some cases,

to arterials by speed-change lanes that allow entering and exiting vehicles to speed up

or slow down without conflicting with through traffic. The speed-change lane for an

off-ramp is known as a deceleration lane, while the speed-change lane for an on-ramp

is known as an acceleration lane. Most ramps connect directly to the adjacent

mainline freeway by means of speed-change lanes. However, a few larger

interchanges have intermediate roadways, known as collector/distributor roads or

C/D roads that connect the ramps and the speed-change lanes. Statistical relationship

for weaving areas were based on the weaving volumes, and for the speed-change

lanes, they were based on the percentage of merging or diverging traffic.

Deceleration Lane Off-Ramp

Deceleration Lane and Off-Ramp

Acceleration Lane OivRamp

On-Ramp and Acceleration Lane

Figure 2.2: Acceleration and Deceleration of Ramp, (AASHTO,2001)

The principal reference for Highway capacity analysis for over 60 years has been US

Highway Capacity Manual. The version of US HCM has been updated from time to time

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started from US HCM, 1965 to the latest version US HCM,2000. The manual presents early

techniques and methodologies for evaluating the capacity of different types of highway

facilities, and for analyzing their operating characteristics under various flow levels. Since the

time that this manual appeared in the field of traffic engineering study, the procedures and

technique have been extensively expose to actual applications. Therefore, this research will

try to evaluate the equation and model of US HCM 2000 method on ramp merging analysis

and check the suitability when it is used on Malaysian traffic condition.

In this process, it is desired to lessen characteristic differences, primarily in speed, between

two traffic demands to allow safe and fast merging maneuvers. To minimize these undesirable

aspects of operation at the junction, acceleration lanes are put into place.

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Input Geometric data - Ramp free-flow speed - Demand j

Demand Flew Adjustment Peak-hour factor Heagy-vehide factor - D n w population factor

(compaia flow rale)

On-tatifi (Mary influence) | Ott-raitipr tQiwarga iwfluanca)

Compute demand Row rale immediately upstream of merge, influence ansa

- Lanes 1 and 2 of the mainline

Compute demand flow rate immediately upstream of 8w diverge influsnea area

- Lanes 1 and 2 of lh mainline

Com pule Capacity Total flow leaving merge arcs Maximum flow entering merge area

Compute Capacity Total flaw departing from diverge area Maximum flow entering Lanes land 2

prior to deceleration lam - Existing legs of the freeway

Wiusled Amend fkaw < Capacity. Musled demand fli i 2 Capacity Adjusted demand flow * Opacify j u s t e d demand rkm 2: Capacity

(WfrdwtfQ C L 0 S F i ) Impute density) (f LQSF- j

c Determine LOS J c Determine LOS f Compute speeKfe j c

3 Compute speeds D

Figure 2.3: Ramps Junction Methodology, (US HCM, 2000)

Vehicle Interaction

Vehicle movements in the vicinity of an on ramp junction consist of lane changes of ramp

driver onto the mainline, lane changes of mainline traffic, and acceleration and deceleration

behavior due to flow turbulence and congestion. These types of behavior cause dynamic

traffic phenomena at on ramp junction.

Lane Changes

Lane change model usually use some assumption, Sparmann, 1986 and Gibbs 1981 suggested

microscopic lane change models that gave basic structure to other lane change models.

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Sparmann mentioned there are unequal usage of slow and overtaking lanes at high flow.

Gibbs explained a lane change process as a three-step chain;

1st- consider needs of lane change, 2nd target desirable lane and 3rd move to target lane with

acceptable gap distance.

The most current (2000) published edition of the HCM defines freeway capacity as "the maximum

sustained 15-min rate of flow, expressed in passenger cars per hour per lane (pcphpl), that can be

accommodated by a uniform freeway segment under prevailing traffic and roadway conditions in a

specified direction. " The HCM 2000 also notes that capacity is dependent upon the freeway's free-

flow speed, and ranges from 2,250 pcphpl (at a 55-mph free-flow speed) to 2,400 pcphpl (at a 70-

mph free-flow speed). The HCM 2000 recognizes the existence of the two-capacity phenomenon

and identifies three distinct flow regimes for freeways: a "free flow" regime, a "queue discharge"

regime, and "congested flow" regime. Furthermore, the HCM 2000 suggests a flow rate drop of

five-percent as a rule of thumb when freeway operations transition from free flow to queue

discharge conditions.

Elefteriadu, 1994, recently addressed the probabilistic feature of breakdown. It was found that

at on ramp junctions, breakdown might occur at lower flows than capacity. It was observed

that at the same site and for the same ramp and freeway flows, breakdown may or may not

occur. Breakdown at on ramp junctions was highly related to large ramp vehicle clusters that

disrupted traffic operations. Therefore, it was concluded that breakdown is a probabilistic,

rather than deterministic, event, and is a function of ramp vehicle cluster occurrence.

Persaud's research, 1998, showed the relationship between flow and probability of

breakdown. The study examined the probability of breakdown at various traffic flow levels.

In the median lane, which restricts truck travel, one minute flow that is 20% larger than queue

discharge flow has only a 10% probability of breakdown, while one minute flow equal to the

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mean queue discharge flow, had a negligible probability of breakdown. It was not surprising

that beyond 2,800 vehicles per hour per lane, the breakdown rises dramatically.

Hall et al (1991) summarized research results in fundamental traffic stream relationships,

namely flow, speed, and density. The research found out that the traditional upper branch

of the speed-flow relationship should be obtained from data collected at any point along the

freeway in the absence of a queue. However, when queuing occurs on the freeway as a result

of breakdown, measurements for the upper branch are appropriate only at locations upstream

from the back of the queue and downstream of the bottleneck, where traffic moves in an

uncontested manner. The study found that several previous studies showed that the endpoint of

the upper branch of the speed-flow curve to occur at approximately 80 km/h (-50 mph).

According to their proposed speed-flow relationship, the vertical portion of the speed-flow

curve, where a wide range of speeds, are observed for the same flow rate represents traffic

conditions in the bottleneck. Within the bottleneck, the mean flow rate remains constant, but the

speed measurement is a function of how far downstream from the start of queue the observations

is made. The research found that it is impossible to obtain data for all regions of the speed-flow

curve at any one station.

Elefteriadou et al (1995) with research study ; Probabilistic Nature of Breakdown at

Freeway Merge Junctions. Previously, capacity related research had yielded deterministic

models that estimated capacity by predicting breakdown based on flow rates, speeds, densities,

or a combination of these measures. These models inherently assumed that breakdown

necessarily follows an "at-capacity" flow condition. In other words, flows and densities were

understood to increase-with a corresponding decrease, in speed-to a point where queues

would form and congestion would occur on the freeway. Although it was recognized that

there was indeed a transition from an uncongested flow condition to forced-flow condition such as

the two-capacity phenomenon, it remained unclear what event(s) triggered the breakdown, and

when and how the breakdown would occur. This paper departed from a deterministic approach to

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