1

5th

International Symposium on Highway

Geometric Design

Vancouver, Canada, 2015

Country Report: Israel

Shy Bassan 1(corresponding author)

Ran Zilbershtein 2

Benny Frischer 3

1 Dr. Shy Bassan, Amy Metom Engineers & Consultants, Ltd., 55A Yigal Alon St., Tel

Aviv 67891, Israel. (Tel: 972-3-6363587; fax: 972-3-6363501)

Email: shy-b@amymetom-ta.co.il ; bassans@ netvision.net.il)

2 Ing. Ran Zilbershtein, Amy Metom Engineers & Consultants, Ltd. Email:

ran@amymetom.co.il

3 Dr. Benny Frischer, Email: frischer@bezeqint.net

Revised: April 27, 2015.

2

ABSTRACT:

Highlights of the geometric design standards for rural (interurban) highways and urban

freeways, published by Israel’s Ministry of Transportation and the National Highways

Company in 2012, are outlined. The preparation of these geometric design standards was

accompanied and approved by a National Highways Company steering committee

composed of highway design, highway safety, and traffic engineering experts from the

MOT, the National Highways Company, the police traffic engineering department, and

highway engineering consulting firms. The major objective of these design standards was

to establish uniform rules and determine design values that would function as guidelines

but not as mandatory regulations. The standards did not intend to limit the engineering view

of thinking, but they do provide a desirable frame in which to present design options and

enable the highway engineer to cope with non-conventional situations during the design

process.

The paper first documents the objectives, structure, and major sections of the standards. A

specific section introduces Israel data and statistics of population, roadway length,

motorization, kilometers traveled, and traffic accidents (with casualties) information. The

second part gives an overview of recent developments in design policy, highway cross

section, stopping sight distance, and horizontal alignment. Finally, it presents topics for

discussion related to sight-distance restrictions in horizontal curve design and left-shoulder

principles on divided highways.

3

INTRODUCTION

The design of interurban transportation infrastructure is important for the economy and for

the fast growth rate of car ownership. The main requisites that highway-design guidelines

should maintain are the following: mobility and accessibility needs, safety of road users,

efficient traffic operations, landscape harmonization, and minimum environmental

deterioration.

The major objective of highway geometric design standards is to establish uniform rules

and determine design values that function as guidelines but not as mandatory regulations.

The standards do not intend to limit the engineering view of thinking, but do provide a

desirable frame in which present design options and enable the highway engineer to cope

with non-conventional situations during the design process.

The 2012 Israeli highway design guidelines are based on a literature overview of recent

international guidelines (AASHTO 2004, 2011; TAC ATC 1999, 2009; New Zealand

TRANSIT 2003; Austroads 2009; DMRB 1999; and German guidelines RAA 2008). The

main innovations of these guidelines relate to the topics of design speed and level of service

policy; sight distance and equivalent deceleration (or equivalent friction) criteria, which

directly affect the outcome of vertical and horizontal alignment; divided highway cross

section, which is related to recent developments in safety-barrier concepts and

technologies; and a new model for correlating horizontal radii and superelevation.

The structure concept of the guidelines is that they should be easily implemented by the

users. Each section includes a brief background, definitions of terms and basic issues, major

considerations and assumptions in determining the recommended design values, warrants if

needed, recommendations of design values, and tables, illustrations, relevant drawings, and

schematic sketches for clarifications.

The design process requires the integration of guidelines from the different topics into one

pack in order to propose an appropriate design solution for a specific project. The

guidelines principally refer to new highway projects but also to upgrading existing

roadways. Exceptional design values that are due to unusual situations and constraints (e.g.,

topography, right of way [ROW], environmental issues) are possible if given approval by

the design authorities after considering a specific problem. The guidelines usually present

minimum or maximum desirable and/or absolute values. The highway engineer should

4

strive not to follow directly these design values in an extreme manner but to implement a

balanced design that incorporates suitable values after considering the topography,

environment, and construction cost, on the one hand, and highway safety and traffic

operations, on the other hand. The guidelines structure enables periodic updating according

to practical experience, safety impacts, and the design policy of Israel’s Ministry of

Transportation.

The guidelines volume depicted in this report is Volume I: Geometric Design of Interurban

Highways: Road Sections. Additional volumes include Volume II: Intersections; Volume

III: Interchanges and Junctions; and Volume IV: Compact Grade Junctions. Volume III and

Volume IV will be updated as one unified volume and are still in practice. This ongoing

work is accompanied by the same steering committee previously described.

An additional volume refers to Road Tunnels and has a specific and expanded geometric

design chapter. It was first published in November 2012 by the Ministry of Transportation

and the National Highways Company. Its authors represent several disciplines (in addition

to highway design and traffic engineering), such as construction, structural engineering,

geo-mechanics, ventilation, fire safety, electric lighting and communication systems, and

environment.

ISRAEL TRANSPORTATION AND TRAFFIC STATISTICS

Population and roadway length:

Israeli population for the second quarter of the year 2015 is approximately 8.32 million.

This estimation does not include foreign workers. The total roadway length in Israel

roadway network estimated for 2013 is: 18,825 kilometers from which 6608 kilometers are

interurban roadways, 10,586 kilometers are urban roads and 1,631 kilometers are access

roads.

Motor vehicles and kilometers traveled:

The number of motor vehicles estimated for 2014 is 2,966,000, from which 2,457,000 are

private vehicles, 328,000 trucks, 124,000 motorcycles, 20,000 taxis, 32,000 buses (and

minibuses), and 4600 special service vehicles.

The total million kilometers travel (MKT) estimated for the year 2013 includes 51,207

[106·veh·km per year] from which: 37,848 private cars, 9099 trucks, 1666 buses (and

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minibuses), 1640 taxis, 872 motorcycles. 31,157 (out of 51,207) is the annual MKT for

interurban roadways estimated for 2013.

The average kilometers traveled per vehicle is: 18,100 km/vehicle. This number is the

equivalent average for several vehicle types: 16400 km/private cars, 26800 km/trucks,

50500 km/minibus, 58800 km/bus, 78200 km/taxi, and 7200 km/motorcycle.

The rate of motorization estimated for the year 2014 is 358 vehicles per 1000 inhabitants,

from which 292 vehicles per 1000 inhabitants (82%) are private cars.

Road accidents with casualties

The number of road accidents with casualties estimated for the year 2013 is 13,048 (9720 in

urban roads and 3328 in interurban roadways). This number includes: 252 fatal accidents

(from which 86 accidents with pedestrian involved and 119 collisions with moving

vehicles), 1413 serious accidents, and 11,383 slight accidents.

The distribution of road accidents by accident type is presented in Table 1:

Table 1: Annual distribution of road accidents with casualties by accident type,

accident severity and road type; Israel 2013

Accident type and severity Total Fatal Serious Slight

Collision with moving vehicle 8057 119 560 8057

Collision with parked (or

stopped) vehicle

136 5 18 136

Collision with a fixed object 664 19 87 664

Hitting a pedestrian 2867 86 538 2867

Injury to passenger on vehicle 50 - 21 50

Overturning 321 16 75 321

Running of road 102 2 26 102

skidding 575 5 53 575

other 276 - 35 276

Total (year 2013) 13048 252 1413 11383

Urban roads 9,720 120 992 8608

Interurban roadways 3,328 132 421 2775

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The relevant number of casualties estimated for the year 2013 is 24,294 from which 277

killed, 1624 seriously injured, and 22,393 slightly injured.

15574 (out of 24294) casualties occurred in urban roads and 8720 (out of 24294) casualties

occurred on interurban roadways.

131 (out of 277) people were killed in urban roads accidents and 146 (out of 277) people

were killed in interurban roads accidents.

The annual accident rate per population [accidents per 100000 inhabitants] is 162. The

annual accident rate per kilometers traveled [accidents per 106·veh·km per year] is 0.255.

Both rates are calculated for the year 2013. The annual accident rate per kilometers traveled

[accidents per 106•veh•km per year] for interurban roadways is 0.11.

Appendix A presents several charts plotting the country statistics information over the years

and comparing the results between Israel and several countries (Greece, Italy, France, UK,

Germany, Canada, U.S.A.). The country statistics traffic and transportation data presented,

is based on Israel Central Bureau of Statistics (CBS) database.

VOLUME I: LIST OF CONTENTS

Section 1: Introduction

Section 2: Basic Design Policy

Highway categories and hierarchy and the basic characteristics of each category;

determination of target speed, design speed, and implementation criteria; design definitions

for divided-highway final construction phase after its initial stage of construction as a two-

lane highway (one-way roadway).

Section 3: Highway Cross Section

The highway cross-section components according to highway categories; pavement width,

including lane, shoulder and median widths; side slopes; forgiving road design and

infrastructure; intermediate specific cross sections (1+1, including separation devices,

passing lanes, and climbing lanes).

Section 4: Sight Distance

Typical sight distance categories for the design of the highway alignment: stopping sight

distance, decision sight distance, passing sight distance, and constrained passing sight

distance.

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Section 5: Horizontal Alignment

Design criteria and details of the design components of the horizontal alignment: horizontal

radii, superelevation, widening, superelevation transition (superelevation runoff, tangent

runout), spiral curves, hairpin curves, design controls, and sight-distance relevance.

Section 6: Vertical Alignment

Design criteria and details of the design components of the vertical alignment: longitudinal

grades and critical length, vertical curve design, grade impact on heavy vehicle

performance (deceleration, acceleration), design control, initial recommendations for

escape ramps.

Section 7: Combinations of Horizontal and Vertical Alignment

Rules for combinations of the design components covered in previous sections for a

complete spatial and aesthetic design; qualitative and visual description of a desirable and

an undesirable design.

Section 8: Highway Capacity and Level of Service (LOS)

Definitions of terms (e.g., flow rate, traffic volume, traffic density, PHF, FFS, PTSF).

Criteria and methodology for computing traffic-flow measures for determining the

highway’s LOS (freeway, urban freeway, multilane divided highway, two-lane undivided

highway), capacity estimation, typical LOS design measures, and other traffic

characteristics. The section refers to HCM 2000 guidelines.

Section 9: Integration of Bicycle Traffic on the Interurban Highway Network

Basic design values, arrangements and warrants for bicycle paths or bicycle lanes in the

highway cross section, typical geometric design components for bicycle traffic.

Section 10: Integration of Public Transport on Interurban Highways

Overview of public transport solutions (bus lane, bus way), integration of public transport

traffic in the cross section, treatment of bus stops and their geometric design elements on

interurban highways.

Section 11: Urban Freeways

Definitions and characteristics, typical design values, geometric design characteristics for

highway sections and interchanges, and urban aspects.

8

Section 12: Integration of Rest Areas on Interurban Highways

Rest area categories, geometric design specifications, warrants, spacing between rest areas,

parking space determination, distance from intersections.

Section 13: Access to Infrastructure Facilities on Interurban Highways

Implementation policy, geometric design specifications for access from existing

intersection and road sections, distance from intersection.

DEVELOPMENTS AND HIGHLIGHTS

Basic Design Policy and Cross Section Elements

Design speed and target speed

The target speed is the desirable travel speed in the defined highway category. The goal is

for most vehicles in the traffic stream to be able to travel at such a speed during free-flow

conditions. It is desirable that the maximum speed limit be similar and actually identical to

the target speed.

The design speed is the safest speed that is determined for the highway geometric design

and its geometric components, which influence vehicle operation. Israeli policy indicates

that in order to provide a reasonable safety margin (similarly to other civil engineering

disciplines and in accordance to international guidelines and literature overview), the value

of the design speed is in practice 10 km/hour faster than the value of the target speed on the

interurban network.

Highway classification and functional characteristics

Interurban highways are classified as follows in the Israeli guidelines:

Freeway:

The freeway is supposed to transfer high traffic volumes at high speed conditions or,

preferably, free-flow speed (FFS). The road is characterized by optimal mobility and no

direct access to any adjacent land use. A freeway has at least two separated roadways with

two lanes or more for each direction of travel. The connection between the freeway and

other highways is made only by system interchanges. The recommended design speed

range for a freeway is 100-120 km/hour. A freeway sign has a blue rectangular perimeter

and the freeway number has usually one blue digit.

9

Urban freeway:

The urban freeway has almost the same geometric characteristics as a freeway. These urban

highways generally cross metropolitan regions, and therefore their interchange/junction

density is higher than that of freeways. The minor road of these interchanges could be an

urban arterial, so that the traffic pattern and daily distribution are different from those on

freeway interchanges in non-urban regions; i.e., there is a higher level of traffic congestion.

The recommended design speed range for urban freeways is 90-110 km/hour. An urban

freeway sign has a blue rectangular perimeter and its number has usually two or three blue

digits.

Major highway:

Major highways transfer high traffic volumes between different regions of the interurban

network at considerably high vehicle speeds. They have a high mobility level for long trips

and limited access to adjacent land use. These highways are usually divided into two

separated roadways, one for each direction of travel; but in certain occasions, they can be

designed as two-lane highways for the first stage of construction. The main difference

between major highways and freeways is the possibility of the major highways’ connecting

to crossing highways at signalized intersections. The divided major highways' design speed

range is 80-110 km/hr or 80-100 km/hour if they include signalized intersections. The two-

lane major highways' (with intersections only) design speed range is 60-80 km/hr. A major

highway sign has a red rectangular perimeter and its number has usually two red digits.

Minor (regional) highway:

The regional highway serves moderate trip lengths and functions as a feeder roadway to the

major highways. The regional highway has a certain level of mobility but serves enclosed

land uses, as well. Regional highways can be designed as divided highways or two-lane

10

highways. The divided minor highway design speed range is identical to that of major

highways. A regional highway sign has a green rectangular perimeter and its number has

usually three green digits.

Local and access roads (low-volume roads):

The principal role of local roads is the provision of access to enclosed land uses. They serve

short-length trips and are usually designed as two-lane, undivided roads. Their design speed

range is 60-80 km/hour. Low-volume roads are categorized as local roads but could have

some reductions in certain design criteria. The sign of local or access road has a black

rectangular perimeter and its number has usually four black digits.

Table 2 summarizes design policies and major cross-section design characteristics of

highways by categories.

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Left sh

ould

er wid

th

(m): d

ivid

ed h

ighw

ay

on

ly

Rig

ht sh

ould

er wid

th

(m)

Lan

e wid

th (m

)

Num

ber o

f way

s

(road

)

Lev

el of serv

ice

Desig

n sp

eed

(km

/hour)

Su

bject

1.2

(2 lan

es per

directio

n)

3.0

(3 o

r mo

re lanes

per d

irection)

3.0

3.6

or 3

.7

(12

0 k

m/h

ou

r)

2 (at least)

C (lev

el terrain)

D (o

ther)

10

0-1

20

Freew

ay

1.2

(2 o

r 3 lan

es per

directio

n)

3.0

(4 o

r mo

re lanes

per d

irection)

3.0

3.6

2 (at least)

D

90

-11

0

Urb

an

freewa

y

1.2

(2 lan

es per

directio

n)

3.0

(3 o

r mo

re lanes

per d

irection)

3.0

3.6

2 (u

sually

)

1 (o

ccasion

ally)

D

Div

ided

: 80

-110

(1)

Tw

o lan

e: 60-8

0

Majo

r hig

hw

ay

1.2

(2 lan

es per

directio

n)

3.0

(3 o

r more lan

es

per d

irection

3.0

(80 k

m/h

our)

2.0

/2.5

(60/7

0 k

m/h

r)

3.6

(80 k

m/h

r)

3.5

(70 k

m/h

r)

3.3

(60 k

m/h

r)

1 (u

sually

)

2 (o

ccasion

ally)

D (lev

el or ro

lling

terrain)

E (m

ou

ntain

ou

s

terrain)

Div

ided

: 80

-100 (1

)

Tw

o lan

e: 60-8

0

Min

or (reg

ion

al)

hig

hw

ay

(1) F

or h

ighw

ays w

ith in

terchan

ges: 8

0-1

10 k

m/h

our. F

or h

igh

way

s with

intersectio

ns: 8

0-1

00 k

m/h

our.

(2) L

ane w

idth

of 3

.0 m

for lo

w-v

olu

me ro

ads.

-

2.0

3.0

-3.5

(60-8

0

km

/hr) (2

)

1

E

60

-80

Loca

l

(access)

roa

d

Hig

hw

ay ca

tego

ry

Ta

ble 2

: Hig

hw

ay d

esign

speed

, LO

S, an

d cro

ss-section

sum

mary

of Israeli

interu

rban

hig

hw

ay d

esign

gu

idelin

es

12

Stopping sight distance and sight-distance design policy

A major purpose in highway geometric design is to ensure that the driver is able to see any

possible road hazard in sufficient time to take action and avoid an accident. Stopping sight

distance (SSD) is the most important of the sight-distance considerations since sufficient

SSD is required at any point along the roadway. SSD is the distance that the driver must be

able to see ahead along the roadway while traveling at or near the design speed and to

safely stop before reaching an object whether stationary or not. SSD can be limited by both

vertical and horizontal curves. The fact that it impacts the design radius of both curves

makes SSD so fundamental in the geometric design process.

The stopping sight distance has two components: (1) the distance traveled during the

driver’s reaction time; (2) the distance traveled during braking. This distance can be

determined by the following formula:

d6.32

VV

6.3

tSSD

2

2

dd

R

⋅⋅+⋅= (1)

where:

SSD – Minimum stopping sight distance (m)

Vd – Design speed (km/hr)

d – Deceleration of passenger cars (m/s2), equivalent to the longitudinal

= friction coefficient (f) multiplied by the acceleration of gravity (g)

tR – Perception reaction time (s), usually 2.5 seconds

The formula assumes level terrain. Ascending grade decreases the SSD, and descending

grade increases the SSD.

The recommended equivalent deceleration rate (d) is based on an SSD model developed by

Lamm et al. (1999) and by research conducted in the U.S. (Fambro et al. 1997, AASHTO

2011). This weighted deceleration takes into account modern braking systems; the quality

of tires, which strongly affects the skidding longitudinal friction coefficient between a wet

pavement and the tires; and the quality of the pavement (e.g. SMA asphalt concrete). The

equivalent friction coefficient and weighted deceleration are presented in Table 3. The

stopping sight distance (SSD) values are presented in Table 3, based on the weighted

deceleration recommended values and Equation 1.

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Table 4: Equivalent Deceleration, Friction, and SSD Values

Recommended for Design Speed

Design speed (km/hr) Recommended

values 50 60 70 80 90 100 110 120

feq: Israel 1994 0.36 0.34 0.32 0.31 0.30 0.29 0.28 0.27

d (m/s2) : Israel

1994 3.53 3.34 3.14 3.04 2.94 2.85 2.75 2.65

feq: recommended 0.427 0.427 0.404 0.383 0.364 0.347 0.343 0.343

d (m/s2) :

recommended

(Israel 2012)

4.189 4.189 3.962 3.755 3.570 3.405 3.363 3.363

SSD (m)

Israel 2012 58 75 97 122 151 183 216 249

Design SSD (m),

rounded for

design

(Israel 2012)

60 75 100 125 155 185 220 250

Table 3 presents the recommended SSD values and the design values for different

countries: Australia (Austroads 2003, 2009), New Zealand (Transit 2003), Canada (TAC

1999), U.S.A. (AASHTO 2011), Germany (RAS 1995), Lamm et al. 1999, and Ireland

(NRA 2007).

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Table 4: Minimum Stopping Sight Distance Design Values (m) for Several Countries

Design Speed (km/hr) Country

tR

(sec) 50 60 70 80 90 100 110 120

Israel (2012) 2.5 58 75 97 122 151 183 216 249

Australia (2003) 2.5 54 71 91 114 140 170 205 245

New Zealand (2002) 2.5 55 75 95 115 140 170 210 250

Ireland (2007) 2.0 70 90 120 133 178 215 255 295

Canada (1999) 2.5 65 85 110 140 170 210 250 –

USA (2011) 2.5 65 85 105 130 160 185 220 250

Germany (1995) 2.0 – 65 85 110 140 170 210 255

Lamm et al. (1999) 2.0 50 65 85 110 140 170 205 245

Israel (1994) 2.5 65 85 110 140 170 200 250 300

tR – Perception-reaction time (seconds).

A graphical relationship between the recommended SSD values and the design speed

values according to the geometric design guidelines of different countries (Table 3) is

presented in Figure 1.

The Canadian SSD design values are identical to Israel (1994) SSD design values for the

design speed range of 50-90 km/hour. Therefore, their lines are unified in the chart and we

can see the Canadian purple line only. The Israeli recommended SSD values (Israel 2012)

are smaller than the Israel (1994) values due to the higher (and improved) equivalent

deceleration rates as presented in Table 3.

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Fig. 1: Comparison of Minimum Stopping Sight Distance in Several Countries

and Recommended Values – Level Terrain

The Israeli recommended SSD values are around the average at the design speed range of

50-80 km/hr. As the design speed rises, the SSD values approach the lower values

(Australia 2003, 2009; Lamm et al. 1999).

The recommended sight distance design (SD) values for decision sight distance, passing

sight distances (PSD), and constrained passing sight distance (CPSD) are presented in

Table 5.

The constrained passing sight distance (CPSD) is the threshold sight distance below which

overtaking is prohibited for all vehicle types. It means that the even fast vehicles should

prevent making passing maneuver under these circumstances. Any two lane highways'

segment which does not satisfy the CPSD should be marked with double solid continuous

line in its centerline. Such signing (in Israel highways and typically internationally) informs

the driver that a passing maneuver is prohibited. Most passenger car drivers practically

need a distance shorter than the conventional (and somehow conservative) passing sight

16

distance (PSD). For example the passing maneuver becomes shorter than PSD when the

vehicle being passed is a slow vehicle and its traffic speed is much lower than the speed

limit; therefore the passing maneuver can be conducted with almost no delay and the driver

of the passing vehicle does not have to accelerate. Such example emphasizes a possible

implementation of the CPSD. Further detail of the elements of passing sight distance (d1,

d2, d3, d4) can be found in NCHRP 605 (2008). Figure 2 introduces these passing

maneuver elements in two lane highways. The Israeli constrained passing sight distance

(CPSD) implementation assumes lower values of these elements.

d1, d2, d3, d4 interpretation:

d1: perception and reaction; d2: passing maneuver; d3: safety margin; d4: distance traveled

by the oncoming vehicle

Fig. 2: Elements of passing sight distance (based on NCHRP 605, 2008).

17

Table 5: Decision SD, passing SD, and Constrained Passing SD Design Values (Israel)

Design Speed (km/hr) Sight distance

(m) 50 60 70 80 90 100 110 120

Decision SD 135 160 190 220 255 290 325 360

Passing SD 335 395 455 510 565 625 * *

Constrained

passing SD 190 220 260 290 320 350 * *

* Speeds applicable only to divided highways in Israel

Implementation of sight distance design values:

The sight distance (SD) design values are implemented on the basis of highway category as

presented in Table 6.

Table 6: Implementation of SD Design Criteria

Highway Category

Sight Distance

(SD)Type Freeway /

Urban

freeway

2-Way Divided:

Major highway /

Minor highway

2-Lane

Undivided:

Major highway

2-Lane

Undivided

Minor (regional)

highway

Local

(access) road

Stopping SD – Always Always Always Always

Decision SD Basic for

design*

Prior to

interchange or

intersection (lane

reduction or

increase)

Prior to

interchange or

intersection (lane

reduction or

increase)

lane reduction or

increase –

Passing SD (km) – – Each

0.05·Vd(km/hr)

Each

0.05·Vd(km/hr) –

Constrained

Passing SD

(CPSD)

– –

For SD < CPSD:

passing prohibited

(100%) by

appropriate

marking

For SD < CPSD:

passing prohibited

(100%) by

appropriate

marking

Enable

CPSD every

3 km at least.

* On freeways and long trips on highly trafficked highways with considerably high operating/target speeds,

without traffic flow interference (such as intersections and access to proximate land uses), the design policy

requires drivers’ SD to be longer than Stopping SD (i.e. Decision SD) in order to make the driving calm and

comfortable.

18

Table 7: Object Height and Driver Eye Height on SD Edges

Sight Distance (SD)

Type

Driver Eye Height

(m) [passenger car]

Object Height

(m)

Stopping SD 1.05

Undivided highway: 0.15

Two-way (divided) highway: 0.60*

Prior to intersection or interchange: 0.15

Decision SD 1.05 0.60

* (road sections generally higher-speed

highways)

Passing SD and

Constrained Passing SD 1.05

1.05* ("the portion of the vehicle height that

needs to be visible for another driver

to recognize a vehicle")

* Concepts based on AASHTO 2011, Fambro et al. (NCHRP 400) 1997.

If the highway is designed as a divided two-way highway, only one way is opened for

traffic in the first stage (i.e. a two-lane highway), then implementation of the SD policy

(specifically for the design of vertical curves) would be based on two-lane highway design

requisites.

Horizontal curve design

A proper design of highway horizontal curves should strive for the maximum curvature or

the minimum radius just under the most critical conditions. It is therefore necessary to

establish an appropriate relationship among the design speed, the horizontal curve radius,

and the superelevation. The minimum radius or the maximum curvature has a limiting

value for a given design speed as determined according to the maximum rate of

superelevation (emax) and the maximum side-friction coefficient (fRmax):

)fe(127

V

)fgeg(6.3

VR

maxRmax

2

d

maxRmax

2

2

dmin +⋅

=⋅+⋅⋅

= (2)

where:

Rmin – minimum radius of horizontal curve (m)

Vd – design speed (km/hr)

g·emax = ae – superelevation acceleration

g·fRmax = afr – friction lateral acceleration

ac = ae+afr – centrifugal acceleration

127 – conversion factor, taking acceleration of gravity as g=9.81 m/s2

19

The use of a smaller radius (sharper curvature) than the minimum radius for the prevailing

design speed might necessitate a non-practical superelevation or side-friction coefficient

beyond the safety limits. Table 8 presents the design values of the basic parameters in

horizontal curve design.

Table 8: Design Values of Basic Parameters in Horizontal Curve Design

Design Speed (km/hr)

Parameter

60 70 80 90 100 110 120

emax

(max superelevation) 0.10 0.10 0.10 0.08 0.08 0.08 0.08

fRmax

max side friction**

0.16 0.13 0.13 0.11 0.10 0.09 0.09

fRmin

min side friction*

0.033 0.030 0.028 0.026 0.024 0.022 0.021

Rmin

min horizontal radius (m) 110 170 220 340 440 565 670

γ: e-fR

distribution coefficient 1.587 1.250 1.275 1.400 1.267 1.133 1.150

* Adapted from Lamm et al. (1999).

** fRmax is required for the minimum horizontal curve radius calculation.

Relationship between Radii Larger than Rmin and the Appropriate Superelevation: e-R

Model

The distribution of the amount of side friction (fR) and superelevation (e) is very important

in the design of horizontal curves with radii larger than the minimum. If a radius selected

for the horizontal curve is larger than the minimum radius (Rmin), then the horizontal curve

should be designed to a smaller superelevation than the maximum superelevation (emax).

The superelevation and the side friction assist in balancing the centrifugal force while

driving along a horizontal curve. The ratio (e/(e+f)) depicts the relative contribution to

balancing the centrifugal force: as this ratio increases, the circular motion relies less on the

side friction, the centrifugal deceleration decreases, and driving becomes more comfortable

and safe along the horizontal curve.

The e-R model assumes a linear relationship between fR and e, and two pairs (fRmax, emax;

fRmin, emin) characterize this relationship. If we define γ as the e-fR linear distribution

20

coefficient based on the superelevation design policy (Bassan 2013), the final of

formulation of the "e-R" model is as follows:

γ⋅+−

⋅γ+= maxmaxR

2

d efR127

V

1

1)R(e , emin ≤ e ≤ emax (3)

where:

R – prevailing radius of the horizontal curve (m)

Vd – design speed (km/hr)

e(R) – prevailing superelevation for R>Rmin

fRmax – maximum side-friction coefficient for maximum superelevation (Table 8)

emax – maximum superelevation suitable for a specific design speed (Table 8)

γ = e-fR – distribution coefficient, based on maximum superelevation policy (Table 8).

This coefficient depends on fRmax, fRmin, emax, emin.

Fig. 3: Linear e-fR distribution model results, emax = 0.10 for 60≤Vd≤ 80 km/hr,

and emax = 0.08 for 90≤Vd≤120 km/hr

21

TOPICS FOR DISCUSSION

Sight-distance restriction in horizontal curve design

Barriers along open highways and walls on tunnels may restrict the available sight distance

in the design of horizontal curves. The minimum radius that is based on the equilibrium of

the centrifugal force, Rmin = V2/(emax+fRmax), is too small for the requirements of stopping

sight distance when there are obstructions along the road (especially the median barrier on

open roadways) that intrude on the line of sight. The limitation of a stopping sight distance

could arise as follows:

(1) On two-lane highways, the inside barrier could restrict sight distance in the right-

bound curve. The horizontal sight-line offset (HSO) could be no more than 4.8 meters

(3 meters of right shoulder plus 1.8 meters of the distance between the centerline of the

right lane and its right edge).

(2) On four (or six)-lane divided highways, the median barrier could restrict sight

distance in the left-bound curve. The HSO could be no more than 4.8 meters (3 meters

of median/left shoulder width plus 1.8 meters of the distance between the centerline of

the left lane and its left edge).

The HSO could be even smaller (i.e. 3.0 meters) if the median shoulder is reduced to 1.2

meters.

The outside barrier restriction is similar to two-lane highways (HSO=4.8 m); however,

since design speed is usually higher, the stopping sight distance is even more restricted. All

this is even more obvious in tunnels, where continuous walls run along the sides.

Table 9 present examples of SSD restrictions on a horizontal curve, based on AASHTO

(2011). Figures 4 and 5 show the restricted SSD line (AB) for two-lane highways and six-

lane divided highways, assuming HSO = 4.8 m and Rmin = 229 m, Rmin = 501 m (for Vd

= 80 km/hr, and Vd = 110 km/hr) correspondingly.

22

Table 9: Examples of SSD restrictions on horizontal curves,

based on AASHTO SSD design values

Design speed, Vd (km/hr)

SSD restrictions

60 70 80 90 100 110 120

Stopping sight distance,

SSD (m), AASHTO 2011 85 105 130 160 185 220 250

Calculated radius

(HSO=4.8m)*

188 287 440 667 891 1260 1628

Calculated radius

(HSO=3.0m) *

301 459 704 1067 1426 2017 2604

Minimum radius (Rmin),

e(max)=8%, AASHTO 2011 113 168 229 304 394 501 667

* R = SD2 / (8·HSO)

Fig. 4: Example of a Restricted SSD Line for a Two-Lane Highway (Vd=80 km/hr)

23

Fig. 5: Example of a Restricted SSD Line for a Six-lane Divided Highway (Vd=110 km/hr)

Median (left) shoulder width

The current Israeli design policy recommends a median shoulder width of 1.2 meters for

divided interurban highways with two lanes per direction and of 3.0 meters for divided

interurban highways with three or more lanes per direction. The concept is that 3.0 meters

enables a stalled vehicle in the left-most lane to move aside to the median shoulder instead

of conflicting at least two traffic lanes while trying to make a safe maneuver to the right

shoulder.

On the other hand, a second opinion supports a narrow left shoulder that is suitable for

highway capacity and high target-speed requirements. The assumption is that drivers are

used to moving to the right shoulder when they have to stop for emergency reasons (i.e.

stalled vehicle or strong personal difficulty in continuing to drive, etc.). This opinion,

however, supports widening the right shoulder (to more than 3.0 meters) and possibly

considering wide emergency lay-bys (generally implemented in working zones) on the

right-hand side in order to provide a wider space for the driver to open the vehicle door and

not be put at risk from the ongoing traffic on the left hand side. Still, a narrow left shoulder

results in smaller HSO and, therefore, in more restricted sight distances on horizontal

curves as discussed earlier.

24

REFERENCES

(1) American Association of State Highway and Transportation Officials (AASHTO)

(2011). A Policy on Geometric Design of Highways and Streets, 6th Edition.

Washington D.C.

(2) Bassan S. (2013). Modeling the relationship between the radius and superelevation in

horizontal curve design. Proceedings of the Transportation Research Board 92nd

Annual Meeting, Washington DC, January.

(3) Design Manual for Roads and Bridges (DMRB) (1999), Vol. 2: Highway Structures

Design, Section 2: Special Structures, Part 9: Design of Road Tunnels, BD 78/99,

HMSO, U.K.

(4) Fambro B., Fitzpatrick K., Koppa R.J. (1997). Determination of Stopping Sight

Distance. National Cooperative Highway Research Program (NCHRP), Report 400,

Transportation Research Board, Washington D.C.

(5) Transportation Association of Canada (1999). Geometric Design Guide for Canadian

Roads.

(6) Guidelines for the Design of Roads (RAS). (1995). Part: Alignment (RAS-L),

Proposals, 1993 and 1995. German Road and Transportation Research Association,

Cologne, Germany.

(7) Guidelines for the Design of Motorways (2011 [2008]). Road and Transportation

Research Association. FGSV. RAA. Germany

(8) Guide to Road Design, Part 3: Geometric Design (2009). AGRD03/09, Austroads,

Sydney, New South Wales.

(9) Harwood D.W., Fambro D.B., Fishburn B., Herman J., Lamm R., Psarianos B. (1995).

International sight distance practices. Proceedings of International Symposium on

Highway/ Geometric Design Practices, pp. 32.1 – 32.23.

(10) ISRAEL Central Bureau of Statistics (CBS). Transport and communications.

http://www.cbs.gov.il/reader/?MIval=cw_usr_view_SHTML&ID=433

25

(11) Lamm R., Psarianos B, Mailaender T. (1999). Highway Design and Traffic Safety

Engineering Handbook. McGraw-Hill, New York.

(12) National Roads Authority, Design Manual for Roads and Bridges (2007). Volume 6:

Road Link Design. Ireland.

(13) NCHRP 605 (2008). Passing Sight Distance Criteria. National Cooperative Highway

Research Program. Transportation Research Board. Washington D.C. USA.

(14) Austroads (2003). Rural Road Design. A Guide to the Geometric Design of Rural

Roads.

(15) TRANSIT New Zealand (2003). State Highway Geometric Design Manual.

26

APPENDIX A:

ISRAEL TRANSPORTATION AND TRAFFIC STATISTICS INFORMATION:

GRAPHICAL PRESENTATION

Roadway length:

27

Motor vehicles and kilometers traveled:

28

Rate of motorization:

29

Rate of motorization (continued):

30

Road accidents with casualties

31

Road accidents with casualties (continued)