Highway And traffic Engineering

1
Highway andHighway and
TrafficTraffic
EngineeringEngineering
INTRODUCTIONINTRODUCTION

OverviewOverview
• This course aims at providing the
student an introduction to
Transportation Engineering. The
course is organized under five
modules. These are:
2

• Introduction to Transporation
Systems Engineering
• Transportation Planning
• Geometric Design
• Pavement Design
• Traffic Engineering
3

ObjectivesObjectives
• Introduction to Transportation
Systems Engineering
• Objective of this module is to give an overview of
the transportaion engineering.
• The focus will be to present a systems approach
where the interaction of humans and the vehicles
and their impact on the society and
transportation.
4

• Transportation Planning plays an
important role in a region's strategy
to improve the performance of the
transportation system.
• Objective of this module is to
describe the basic characteristics of
transportation planning and of the
models used by transportation
planners.
5

• Geometric Design of highways deals with the
dimensions and layout visible features such as,
alignment, sight distances and intersections.
• Objective of this module is to describe highway
design objectives, constraints and controlling
factors, also to describe the criteria, standards
and engineering procedures used to design
principal elements of the highway alignment, and
highway cross sections.
6

• Pavement Design based on empirical and
mechanistic relations between materials,
geometry and performance.
• Objective of this module is to understand the
process of collecting information necessary for
successful design of flexible and rigid pavements,
including traffic data, material properties and
other environmental factors.
7

• Traffic Engineering includes traffic signs,
markings, traffic signals, islands etc.
• Objective of this module is to understand
the basic parameter of traffic engineering
and the methods to estimate those
parameters.
• It examines ways to promote operational
efficiency and safety through the use of
traffic control devices.
8

9
S. # TOPICS
Lecture
Required
01 Transportation system: Introduction 1
02 Evolution of Transportation /Highway Development in Pakistan 1
03 Highway planning 1
04 Geometric design: Introduction/ Design controls 1
05 Design vehicle 1
06 Functional classification of roads and Design speed 1
07 Design Driver 1
08 Design Volume 1
09 Sight Distances 3
10
Cross section elements (with of travel lane, shoulders, medians
……)
2
MEHRAN UNIUVERSITY OF ENGINEERING AND TECHNOLOGY
RM-001/00QSP-004 Dec.01.2001
TENTATIVE TEACHING PLAN
DEPARTMENT/INSTITUTE/DIRECTORATE: CIVIL ENGINEERING
Name of Teacher: Prof. Dr. Abdul Sami Qureshi
Subject: Highway & Traffic Engineering Batch: 08CE- Year: Final Term: 1st
Term Starting Date: 03-01-2011 Term Suspension Date: 24-04-2011

10
09 Cross slopes 1
10 Horizontal Alignments: Introduction 1
11 Horizontal curves 2
12 Transition, curves 2
13 Super-elevation 2
14 Curve widening 1
15 Vertical Alignments: Introduction 1
16 Grades 1
17 Vertical curves 2
18 Pavement Design: Introduction 1
19 Early road construction methods 1
20 Design of flexible design 4
21. Design of rigid pavement 4
22. Maintenance of pavement 2
23. Traffic Engineering: Introduction 2
24. Volume studies 2
25. Highway safety 3
26. Highway capacity 3
27. Traffic control devices 1
28. Traffic signals 3
TOTAL 52

REFERENCESREFERENCES
1. HIGHWAY ENGINEERINGPAUL
H. WRIGHT/ KAREN K. DIXON
1. TRANSPORTATION ENGINEERING
C. JOTIN KHISTY-B. KENT LALL
1. HIGHWAY ENGINEERING
J. KHANNA
1. THE HAND BOOK OF HIGHWAY ENGINEERING
T. F. FWA
1. http://nptel.iitm.ac.in/
2. http://ocw.mit.edu/OcwWeb/web/home/home/in
dex.htm
3. HIGHWAY CAPACITY MANUAL
11

Overview ofOverview of
TransportationTransportation
EngineeringEngineering

What isWhat is
TRANSPORTATIOTRANSPORTATIO
N?N?

Transportation SystemTransportation System
Definition of Transportation Modes
• A transportation system is an
infrastructure that serves to move people
and goods efficiently.
• Efficient = safe, rapid, comfortable,
convenient, economical, environmentally
compatible.

Transportation SystemTransportation System
Major transportation subsystems
• Land transportation: highway, rail
• Air transportation: domestic,
international
• Water transportation: inland, coastal,
ocean
• Pipelines: oil, gas, other

TransportationTransportation
Movement of
persons and goods
over space
A B

MAJOR INTERACTING COMPONENTSMAJOR INTERACTING COMPONENTS
InfrastructureInfrastructure
Vehicle / ServiceVehicle / Service
Users /Users /
SubstanceSubstance

Users / ContentUsers / Content
• People → Passenger Transportation
• Goods → Freight Transportation
Shareoftotalpassengersor
tons-km
Distance
Passengers
Commuting
Shopping
Recreation
Business
Tourism
Migration
Waste disposal
Local distribution
Trade
Energy & Raw Materials
Freight
Source: Dr. Jean-Paul Rodrigue, Dept. of Economics & Geography, Hofstra University.

Users / substanceUsers / substance
Passengers Freight
Board, get off and transfer
without assistance
Must be loaded, unloaded
and transferred
Process information and
act on it without assistance
The information must be
processed through logistics
managers
Make choices between
means of transport often
irrationally
Logistics managers make
choices between means of
transport rationally

Vehicles / ServicesVehicles / Services

InfrastructureInfrastructure
ngram Publishing Royalty Free Photograph

Evolution of
Transportation /Highway
Development in Pakistan
36

Evolution of TransportationEvolution of Transportation
2000
Maritime Road Rail Air
180019001950
Docks
Locks
RailsOmnibus
Steam engine
Electric motor
Balloons
Dirigibles
Iron
hulls
Internal combustion engine
Metro
TramwayAutomobileLiners
Bicycles
PlanesTrucks
Buses
Electric
car
Hydrogen
car
Airfoils
Super
tankers
TGV
Maglev
Jet engine
Jet Plane
Container
ships
Helicopters
Bulk ships
Highways
Jumbo Jet

1500-1840 Average speed of wagon and sail
ships: 16 km/hr
1850-1930 Average speed of trains: 100 km/hr.
Average speed of steamships: 25 km/hr
1950 Average speed of airplanes: 480-640 km/hr
1970 Average speed of jet planes: 800-1120 km/hr
1990 Numeric transmission: instantaneous

100
500
1000
1800 1900 20001850 1950
50
250
750
Stage Coach
Rail
Automobile
HST
Propeller Plane
Jet Plane
Liner
Clipper Ship Containership
Road
Maritime
Rail
Air
Km
/hr

• The TGV (French: Train à Grande Vitesse, meaning high-speed train) is
France's high-speed rail service
• A TGV service previously held the record for the fastest scheduled rail
journey with a start to stop average speed of 279.4 km/h (173.6 mph),[2][3]
which was surpassed by the Chinese CRH service Harmony express on the
Wuhan–Guangzhou High-Speed Railway in 2009.
• Maglev (magnetic levitation), is a system of transportation that suspends,
guides and propels vehicles, predominantly trains, using magnetic
levitation from a very large number of magnets for lift and propulsion.
• A hydrogen vehicle is an alternative fuel vehicle that uses hydrogen as
its onboard fuel for motive power
• Buses, trains, motorcycles,, ships, airplanes, submarines, and rockets can
already run on hydrogen, in various forms.The current land speed record
for a hydrogen-powered vehicle is 286.476 mph (461.038 km/h)
40

41
• Now a days Supertankers has a length overall of 380.0 metres
(1,246.7 ft) and a cargo capacity of 3,166,353 barrels
(503,409,900 l).

43
A jet aircraft is an aircraft propelled by jet engines. Jet aircraft
generally fly much faster than propeller-powered aircraft and at
higher altitudes – as high as 10,000 to 15,000 meters (about 33,000
to 49,000 ft).

44
A jumbo jet is a term used to describe a large aircraft, most
commonly the Boeing 747, after Jumbo, a famous elephant.
The 747-400, is among the fastest airliners in service with a high-
subsonic cruise speed of 570 mph, 920 km/h and can accommodate
more than 500 passengers.

What isWhat is
TRANSPORTATIOTRANSPORTATIO
N ENGINEERINGN ENGINEERING
??

Transportation EngineeringTransportation Engineering
• One of the specialty areas of civil
engineering
– Development of facilities (roads ,
railways, airports, Bus stops,..) for the
movement of goods and people
– Planning, design, operation and
maintenance
• Multidisciplinary study

• Transportation engineering:
• Science deals with efficient, safe, economical, comfortable
and speedy movement of goods and persons.
•
• Highway Engineering:
• It covers the construction of roads and providing the facilities
to road user and planning for safety or road vehicles etc.
•
• Railway Engineering:
• It deals with the lying of the railway track for movement of
heavy locomotives, wagons etc. it deals also with control of
movement with help of station yards.
•
47

• River and Harbour Engineering:
• Science deals with the development of docks and harbour
on sea or river shore for departure and arrival of ships and
other facilities for loading, unloading etc.
•
• Airport Engineering:
• Technique of development of runways, taxiways,
hanger, terminal building and control devices etc are dealt
in Airport engineering.
48

• An interesting / exciting area !
• Employers
– 50% government
– 40% consultants
– 5% research, teaching
– 5% other rail, trucking firms, etc.

Highway
Development in
Pakistan
51

Development of road:Development of road:
• Road extensively used before advent of railways
• Major roads work ignored but attention on feeder roads.
• End of 2nd
world war provided surplus military vehicles of
civilization.
• Boom to road construction and 1930 -- automobile age
•
• Highway related activities:
– motor vehicle registration
– highway expenditures
– road milage pass-Km, Tonn – Km.
– motor fuel consumption….
52

• Infrastructure and Economic
• Growth
• 􀂄 In the following slide a graph is presented that clarifies
the role of
• infrastructure in economic development (Source: Queiroz et
al, 1992
• – World Bank Working Paper).
• 􀂄 This slide shows a plot of the length of paved roads that
a country
• has versus its GNP
• 􀂄 98 countries were surveyed to plot this graph
• 􀂄 A clear correlation emerged between the Length of
paved roads
53

• (LPR) and the per-capita GNP (PGNP) according to the
following
• equation
• 􀂄 PGNP = 1.39 (LPR)
• 􀂄 This indicates that the more physical infrastructure a
country has (in
• this example we consider only transportation infrastructure,
but this
• relationship holds true for other types of infrastructure as
well), the
• greater the economic stability and vice versa.
54

The Infrastructure CrisisThe Infrastructure Crisis
• Despite the importance of infrastructure for economic and
social well-being, we are faced with several problems
• Infrastructure in developed countries is old, unreliable,
inefficient and in need of replacement.
• 􀂄 The USA is embarking on a major plan relating to
infrastructure spending
• 􀂄 In developing countries, infrastructure is often not
available
56

• 􀂄 Large portions of urban and rural populations in developing
countries haveinadequate access to water and sanitation
• 􀂄 Power supply is non-existent or unreliable and people are faced
with frequent power-cuts
• 􀂄 Quality of road infrastructure is often bad, leading to long
travel times and increased vehicle maintenance costs. Width of
roads is also often a constraining factor leading to traffic jams and
blocks.
• 􀂄 Several of these problems currently hold true for many areas in
India as well.
• 􀂄 This is therefore a golden opportunity for engineers with
technical as well as managerial and policy level knowledge of
these issues, since there is a huge demand for such people to
enter the workforce and solve the worlds infrastructure
inadequacies.
57

Why do we have so manyWhy do we have so many
problems with infrastructure?problems with infrastructure?
• 􀂄 This particular question and ways in which to solve it will
• the focus of this entire course. It is therefore impossible
• to answer this question right away. Before we conclude
• this session, we list out a few of the causes for the failure
• to provide adequate infrastructure
• 􀂄 Lack of funds
• 􀂄 Lack of implementation and management capabilities
• 􀂄 Corruption, bureaucracy and unfair competition
• 􀂄 Land acquisition issues involving dealing with displaced
people
• and special interest groups
• 􀂄 etc
58

INTRODUCTIONINTRODUCTION
PAKISTAN HIGHWAY SYSTEMPAKISTAN HIGHWAY SYSTEM
PAKISTAN
TRANSPORTATION
SYSTEM
 It contributes 11% in country's GDP & 5.46 % in employment
labor force
 It accounts for 90% passenger and 96% for freight traffic.
 Road transport is to be Considered the backbone of Pakistan
transport.
 It Carries about 80% of the Pakistan total transport.

60
Passenger Transportated in
Pakistan
2% 16%
82%
1 2 3
82% through Roadways
16% through Railways
2% with Airways

61
82
16
2
0
20
40
60
80
100
1 2 3
Cargo Transported in Pakistan

PAKISTAN HIGHWAYPAKISTAN HIGHWAY
SYSTEMSYSTEM
• 1947 – 49959Km
• 9759 Km (High type)
• 40200 Km (Low type... Earthen)
•
• 1985 – 118211 Km 5160 Km (High type) Growth Rate 2.29%→
• 1998 – 180000 Km (urban as well as rural)
• 2008-2009 -- 258,350 kms
• 23 National Highways, 7 motorways, 3 expressways & 3
Strategic roads.
• The length of high type road is 176,589kms and low type
road is 81,761kms.
• The total length of National Highways, Motorways,
expressways and strategic roads is 11857kms. Which is
4.6% of total length.
• Quite development but not satisfactory, when compared with
other countries area and population wise. 62

97
Country Length (Km) per
100 Km2
Length (Km) per
1000 Km2
Japan
France
USA
Germany
India
Srilanka
274
174
64
168
50
38
>150
>120
--
>100
Pakistan 14 0.43
Pakistan Poorest Country
Even India has 3 to 4 times greater
Kilometerage

98
Lanes
1 Lane
2 Lane
2 – 3 Lane
3 – 4 Lane
> 4 Lane
61%
29%
5%
4%

Challenges For PakistanChallenges For Pakistan
• Increased traffic volume due to increased vehicle
ownership
• Dire deficiency of 346000Km to serve people
efficiently.
• To widen existing road network from single lane
to two
• If 3000Km constructed every year even then
require 100 years
• Big potential for opportunities for Highway
Engineers.
99

Existing Challenges for PakistanExisting Challenges for Pakistan
 Now- days over half the road is in poor condition and most of the
roads has been failed before their design life.
Failure is defined in terms of amount of cracking, rut depth, surface
roughness, skid resistance or other indicators
 The various factors which may cause the failure of pavement
are:
 Overloading
 Unsatisfactory Compaction
 Inadequate Drainage
 Frost action
 Quality of Material
 The material used does not compliance the specification.
 Laboratories do not follow the proper process in testing.
 Equipments are not properly working.
 End products are not according to specification and give less
results as compared to the required.
 This problem can be improved or partially solved by proper
“Quality assurance in testing of highway materials”.

HIGHWAYHIGHWAY
PLANINGPLANING
101

Highway Planning:Highway Planning:
• The making of plans and engineering investigation of the
project on a scientific basis rather than haphazard for
future Construction, maintenance and operation (Or for
new project or explained programs) is called Highway
Planning.
• A summary of major Data required for Highway Planning
are:
• An inventory of all rural roads (Width type, condition and
road bridges….)
• An estimate of volume and character of traffic
• Source of highway financing of the state and subdivision.
• An estimate of the number of the motor vehicles
ownership.
• Road life studies based on past records of construction and
reconstruction, from which service life can be estimated.
•
102

Object of Highway Planning:Object of Highway Planning:
 The proposed road should provide efficient, safe,
economical comfortable and speedy movements.
 It should have maximum utility within available
resources and other restraints.
 It should meet for anticipated future developments and
social needs.
 Highway planning should evolve financing system and
recommend changes in taxes and budget procedures.
 Highway Planning helps in phasing the road
development programs from financial consideration and
top most needy condition.
103

Principal of Highway Planning:Principal of Highway Planning:
• Equipped with traffic sign boards or
statutory provision for regulation
• Importance of road should be only
on traffic demand
• Road should from integral part of
network and form a part of
development schemes.
• There should be provision of
maintenance funds
104

Deficiencies of Highway planning:Deficiencies of Highway planning:
• No correlation to transport needs.
• No any base on systematic transport
survey
• No asses of base and horizon year traffic.
• No evaluation for qualitative
improvements in terms of geometric,
structural integrity, riding surface etc.
• No relation between transport plans with
other sector like agriculture, industry etc.
105

STUDIES/ DATA COLLECTIOINSTUDIES/ DATA COLLECTIOIN
REQUIRED FOR EFFICIENT PLANNINGREQUIRED FOR EFFICIENT PLANNING
• Field studies are conducted to collect the
data for assessment of road length
requirement for an area.
• Intelligent approach for efficient planning
• Helps in protecting any project from short
sightedness and shifting policies
• Detailed of surveys/studies are given
below for the development of a road
Project.
106

ECONOMIC STUDIESECONOMIC STUDIES
• Following details should be collected for economic studies
to determine the details of services given by the proposed
road to population & products of area which are useful in
estimating the economics involved
• Population and its distribution Trend of population growth
• Agriculture and industrial production and their listing in
classified groups and develop their future trends
• Per capita income
• Existing facilities like post office, School, Banks , etc
(Regarding communication, education and recreation to
estimate the Source of traffic)
• Country Highway mileage, its condition and distribution.
107

Financial Studies:Financial Studies:
• It is important to study various financial aspects like source
of income and their methods adopted to mobilize the fund
for project
• Source of income
• Estimating revenue from road transport
• Living standards
• Resources from local level, toll, Vehicle registration and
court fines etc.
108

Traffic and road use studies:Traffic and road use studies:
• Details of existing traffic, their volume and the pattern of
flow etc is necessary to plan for improvement in road
system or for construction of new road.
• Traffic Volume per day, AADT and peak hourly traffic
volume
• Origin and destination study.
• Mass transportation facilities
• Accidents, their cost analysis and causes
• Future trend and growth in traffic volume and goods traffic
• Growth of passenger trips and trend in the choice of mode
• Type of vehicle, gross weight, axle load, weight and length
or vehicle , commodity hauled etc are value able for road
design and regulation purpose
109

Engineering Studies:Engineering Studies:
• Detail of topography, Soil, Drainage and problems
related to construction and maintenance to be
investigated to chalk out plan. It needs
• Topographic survey
• Road location and alignment studies
• Soil surveys
• Location and classification of existing roads and
their types
• Road life studies, construction methods and
maintenance problems
• Special problems in drainage
110

PROJECT REPORT:PROJECT REPORT:
Project report should contain following details
• Introduction of project along with history and graphical
details
• Main requirements and factor of proposed alignment
• Details of alignment with respect to proposed width/
guage , gradients, length and levels of points
• Description about other proposed alternatives
• Details of proposed alignment with various dates and maps
• Specifications of the constructional standards
• Conclusion and recommendation of proposed project of new
railway line / High way.
111

Drawing to maps prepared along withDrawing to maps prepared along with
project report:project report:
• Overall map of that region to a scale 1 cm = 2Km.
• Index map of the area to a scale of 1 cm = 2.5 Km.
• detailed plan of proposed alignment with L section
• Contour plans and L section at bridge & culvert
• Plans of Bus stop to scale of 1 cm = 50 cm (Bus stop,
Rest , filling stations, Rest places)
• detailed drawing of all the bridges and buildings to a scale
of 1 cm = 1 m
• plan of level crossings to a scale 1 cm = 50 m
• details of important structures lying with 300 m on either
sides of the proposed rout
• Cross section at every important point should be prepared.
112

GeometricGeometric
DesignDesign
113

Geometric designGeometric design
• Criterion for the Selection of best
rout (Corridor Study).
• Design of visible features
114

Corridor StudyCorridor Study
The objective of the corridor study (highway
location study) is to establish highway's
centerline (baseline) and cross-sections in
relation to the terminal points and to the
topography of the area through which the
highway will pass.
The proposed highway route must be:
1. Economically justifiable,
2. Technically feasible, and
3. Environmentally acceptable.

116
Basic Principles for HighwayBasic Principles for Highway
LocationLocation
• There are an infinite number of ways to get from point A to
point B.
• selecting the best path between two points is called
Highway location
• Visible features of a road are Straight section; Transition
curve; Circular curve; Vertical curve; Cross-sections
• Visible features Roadway must be connected with each
other to design a road that provides for the easy flow of
traffic, while meeting design criteria and safety
standards.
Garber and Hoel, 2002

117
Factors Considered in the Selection ofFactors Considered in the Selection of
the best routthe best rout
• Topography
• Social and demographic characteristics
(including land use patterns)
• Terrain and soil conditions

118
Factors Considered in the LocationFactors Considered in the Location
ProcessProcess
• Directness of route
• Serviceability of route to industrial and
population areas
• Crossing of other transportation facilities (roads,
railroads, rivers)
– Intersect other roads at right angle

119
ProcessProcess
• Environmental
– Animal habitat
– Location of recreational, historic and
archeological sites
– Noise, air, and water pollution

120
ProcessProcess
• Economic
– Construction
– Maintenance costs
– Road user costs
– Road user benefits (i.e. travel time)
– Adverse effects such as dislocation of
people or businesses

ENGINEERINGENGINEERING
SURVEY FORSURVEY FOR
HIGHWAYHIGHWAY
LOCATIONLOCATION
121

ENGINEERING SURVEY FOR HIGHWAYENGINEERING SURVEY FOR HIGHWAY
LOCATIONLOCATION
• This survey is also called Route Survey and propose is to fix
the final road alignment
• and carried out in four stages.
• Map study
• Reconnaissance survey (Recci) Survey
• Preliminary survey
• Final location and detailed survey
122

124
300
A
300
A
400
350
475
B
A
350
340
330
375
100
B
20%
20

Costs
vs.
Desig
n
Level
Alt. 1
Alt. 1

Costs
vs.
Desig
n
Level
Alt. 2

Costs
vs.
Desig
n
Level
Alt. 2
Alt. 1

Map Study:Map Study:
• It suggests the possible routes of the projected road out of
several likely alternative routes from available
• It gives the rough guidance about the route to be further
survey in the field
• The main features likes rivers hills valleys etc available on
maps helps in locating the alignment roughly avoiding
ponds and lakes.
• Give idea about approximate location of bridges, tunnels
etc.
• From map study it is also possible to drop a certain route
due to unavoidable obstructions.
• Topographic map having 15 or 30 meter contour intervals
could be used for this study.
130

::
Recci SurveyRecci Survey
• The main object of Recci survey is to examine in the field
the general characteristics of a stretch of land along the
proposed alternatives routes marked on the map.
• Following facts (not available in maps) are collected during
recci survey.
• e.g. Marshy land, ridge, hills, permanent structures and
other type of cross drainage structures, soil type along the
route, proximity of materials and labor etc.
• For that survey plans, land use plans, air photos, stream
and drainage maps etc. are used.
• As a result of recci survey a few alternative alignment (two
or three)may be chosen for further study.
• Recci survey is not required for minor relocation of an
existing road.
131

Preliminary Survey:Preliminary Survey:
• The preliminary survey decides the final route among two
or three routes after studying the advantages and
disadvantages.
• It is carried about with great accuracy and with critical
study
• Because the final route selection depends upon it and has
much effect on investment.
• Generally preliminary survey work is more or less an open
traverse survey of 60 to 300 meters wide belt along the
centre line of proposed (2 or 3) alternatives.
•
132

Preliminary SurveyPreliminary Survey
Preliminary Survey is done especially to collect below
information
• Geological information like soil, rocks, etc and their bearing
capacity
• Details of existing culverts, bridges, tunnels, irrigation
canal works etc.
• Position and details of level crossing proposed.
• Availability of construction material, labors, water along
proposed alignment.
• H.F.L. and L.W.L. of all river streams on paved alignment.
• Preliminary survey work is done mostly with Tachometer,
Level instrument, Prismatic compass and Plane table.
133

Preliminary SurveyPreliminary Survey
• All physical features e.g. building, posts of existing roads
and their radius of horizontal curves should be marked and
measured from transverse line.
• Grades at every 50m interval.
• Cross section at every 500m intervals.
• In order to have general idea to final centre line of
alternative alignment conforming to the design standards is
tried on plans.
• More suited alternatives from economic and other
consideration is finally chosen.
134

Location Survey:Location Survey:
• Here full detailed survey work will be done along most
economical route, determined by the preliminary survey.
• The final route marked on prepared plan is known paper
location, in which details of gradient, curves, contour,
direction crossing of streams etc are worked out.
• Then transfer of alignment from paper to ground is done in
the Final location Survey.
135

Final Location SurveyFinal Location Survey
• It consists in fixing up the centerline of the proposed
highway on the ground with the horizontal and vertical
controls. Final location involves two main operations.
• Sketching out of final centerline of the field.
• Beginning and end of circular and transition curves and all
other intermediate transit points (250m C/C) should be
fixed on center in case of new roads or by means of spikes
in the case of existing road.
• A single datum should be used for level works.
• Permanent bench marks should be established at every
250m, and at all drainage structure or on famous
reference point.
136

Final Location SurveyFinal Location Survey
– Detailed cross section at stations every 50m in plain
and at 25m in rolling terrain apart should be taken.
– In addition above other cross sections at the
beginning, middle and at end of spiral and of
circular curves should be taken up to the right-of-way
limits.
Detailed leveling.
– Longitudinal profile should also be taken for a stretch at
least 200m beyond then limit of the project.
• After protecting the points referencing Centre line the
construction survey is started.
137

139
HOW IS HIGHWAYHOW IS HIGHWAY
LOCATION DETERMINED?LOCATION DETERMINED?
When Your Land Is Needed For Highway Use
Author: Stephen D. Holowach 7/23/99
http://www.119south.com/presentation/
• Establish the most direct and useable highway facility
at the least possible cost to the public.
• For undertakes intensive studies on several possible
routes
• Select the route that has the least possible
inconvenience or injury to the public and the private
landowner.
• Analyze the data concerning the economy, population
needs and traffic volume trends for the area under
study.
• Make the Aerial and ground surveys to consider factors
such as safety, drainage and soil types.
• Hold the public meetings to discuss the proposed
alternate locations.

140
RIGHT-OF-WAY?RIGHT-OF-WAY?
• Right-of-Way is the term used to describe the right
to pass over another’s land.
• When the government acquires land for Highway
Purposes it is actually obtaining “Right-of-Way” over
land on which a public road ultimately will be built.
• It is a Constitutional right of the government to
acquire land for public purposes
• The every Department of Transportation will execute
this right only when it will benefit the public.

141
What does a location study include?What does a location study include?
http://www.virginiadot.org/projects/studybris-http://www.virginiadot.org/projects/studybris-
coalfieldprocess.aspcoalfieldprocess.asp
Fully defining the project, or "scoping“
•This process is an opportunity to identify
issues and obtain comments from
agencies, jurisdictions and the public
early in the planning process.
•A "purpose and need" statement and the
goals and objectives of the Location Study
will be developed.

142
What does a location study include?What does a location study include?
(VDOT)(VDOT)
http://www.virginiadot.org/projects/studybris-http://www.virginiadot.org/projects/studybris-
coalfieldprocess.aspcoalfieldprocess.asp
Alternatives Identification
•Use technical data such as traffic counts and aerial
mapping and early environmental evaluations to develop
several possible road locations, or alternatives, within the
Study corridor.
•In this phase is to identify reasonable alternatives that
consider the input provided from communities, businesses
and individuals as well as regional concerns.
•Consider a number of new locations as well as upgrades
of existing roads.
•Look at the deficiencies of the existing transportation
network, including safety concerns and any planned
improvements along the study corridor.

143
http://www.virginiadot.org/projects/studybris-coalfielddefault.asp

145See also: http://www.interchange77-81.com/project_overview/default_more.asp

HIGHWAYHIGHWAY
ACTIVITIESACTIVITIES

147
4 ACTIVITIES4 ACTIVITIES
1. The existing physical
structure needs major
repair/replacement
(structure repair).
http://www.k5kj.net/jarrell.htm

148
2. Existing or projected
future travel demands
exceed available
capacity, and access to
transportation and
mobility need to be
increased (capacity).
http://www.ens-
newswire.com/ens/sep2002/2002-09-19-
06.asp

149
3. The route is experiencing
an inordinate number of
safety and accident
problems that can only
be resolved through
physical, geometric
changes (safety).
http://www.ems.ucla.edu/traffic/
ta10.htm

150
4. Developmental pressures
along the route make a
reexamination of the
number, location, and
physical design of access
points necessary
(access).

GeometricGeometric
DesignDesign
151

Geometric DesignGeometric Design
• Geometric design is the aspect of
transportation engineering that deals with
• A) Selection of the best path between two
destinations.
• B) Deals with the design of visible features
of a road
• A good geometric design has to balance
balance operational efficiency, comfort,
safety, convenience, cost, environmental
impact, and aesthetics.
152

Geometric DesignGeometric Design
• Geometric design deals with the
design of visible features
• Visible features are
– Straight section
– Transition curve
– Circular curve
– Vertical curve
– Cross-sections
153

Highway And traffic Engineering

Design ControlsDesign Controls
170

Design ControlsDesign Controls
Factors which control the visible
features of the Highway
• Design vehicle
• Design speed
• Design volume
• Design driver
• Sight distance
• Highway classification……….
171

DesignDesign VehicleVehicle
A design vehicle represents an individual
class in a conservative manner.
• passenger cars (compact, subcompact,
light delivery trucks),
• trucks (single-unit, tractor-semitrailer
combinations, trucks with full trailers),
• buses/recreational vehicles (single-
unit, articulated, school buses, motor
homes, passenger cars pulling trailers or
boats).

174
Design VehicleDesign Vehicle
• Design Vehicle – largest (slowest,
loudest?) vehicle likely to use a facility
with considerable frequency
• Three characteristics that affect almost
all aspects of highway design
– Physical
– Operating
– Environmental

175
Physical CharacteristicsPhysical Characteristics
• Type (GB defines 20 design vehicle types)
– Passenger Car P
– Buses B
– Trucks SU, WB
– RVs
– Farm tractor
• Size
– Length
– Height
– Weight
– Width
– Height of driver’s eye (car: 3.5’ – avg., truck: 7.6’ –
high side)
– Center of mass

Minimum Turning PathMinimum Turning Path
Passenger CarPassenger Car
Minimum turning path
is defined by the
outer trace of the
front overhang and
the path of the inner
rear wheel.

Minimum
Turning Path
Double-Trailer
Combination

TUNNEL RAMP UNDER
CONSTRUCTION

185
Dimensions of Design Vehicle TypesDimensions of Design Vehicle Types

186
Operating CharacteristicsOperating Characteristics
• Acceleration
• Deceleration and braking
• Power/weight ratios
• Headlights
• Friction (ball bank)

187
EnvironmentalEnvironmental
CharacteristicsCharacteristics
• Noise (noise meter)
• Exhaust
• Fuel Efficiency
• Dust (particulate and VOCs from tires
and brakes)

Vehicle PerformanceVehicle Performance
Characteristics
acceleration
deceleration
difficulties in maintaining steady speed
Use
intersections
freeway ramps
climbing or passing lanes, and
turnouts for buses

Vehicle PerformanceVehicle Performance
Exhibit 2-24

Vehicle Performance
Exhibit 2-25

Vehicles on GradesVehicles on Grades
• Passenger cars
– The upgrades up to 3% have a slight impact on
passenger cars.
– On steeper grades this effect becomes more
pronounced.
– No special consideration is needed.
• Trucks
– The effect of grades on truck speeds can be quite
strong (Exh. 3-53, 3-60).
– The truck with the mass/power ratio 120 kg/kW is
selected to represent heavy vehicles (conservative
assumption).
• Recreational vehicles
– Consideration of recreational vehicles on grades can
be justified for recreational roads with the low
percent of trucks (for example, to consider an
additional lane).

Effect of grade on truckEffect of grade on truck
performanceperformance
Crawling
speed

Effect of differential speedEffect of differential speed
on crash rateon crash rate

Critical Lengths of GradesCritical Lengths of Grades

195
Effect of grade on RVEffect of grade on RV
performanceperformance

Maximum Side FrictionMaximum Side Friction
Exhibit 3-
11

Design SpeedDesign Speed
Design VolumeDesign Volume
198

199
Design Speed andDesign Speed and
Design TrafficDesign Traffic
ConceptsConcepts

200
 Get familiar with design speeds
for functional classes
 Describe traffic demand and
determine for roadway design
 Define ADT, AADT, DHV, D,
DDHV, K-Factor, and T

201
• Posted speed = speed limit
• Operating speed = free flow (spot
speed)
• Running speed = length of
highway section ÷ running time
• Design speed = selected speed
used to determine geometric
design features

Design speedDesign speed
• Design speed is the single most important factor
that affects the geometric design.
• It directly affects the sight distance, horizontal
curve, and the length of vertical curves.
• Since the speed of vehicles vary with driver,
terrain etc, a design speed is adopted for all the
geometric design.
• Design speed is defined as the highest continuous
speed at which individual vehicles can travel with
safety on the highway when weather conditions
are conducive.
202

• Design speed is different from the legal speed
limit which is the speed limit imposed to curb a
common tendency of drivers to travel beyond an
accepted safe speed.
• Design speed is also different from the desired
speed which is the maximum speed at which a
driver would travel when unconstrained by either
traffic or local geometry.
203

• Since there are wide variations in the speed adopted by
different drivers, and by different types of vehicles, design
speed should be selected such that it satisfy nearly all
drivers.
• At the same time, a higher design speed has cascading
effect in other geometric designs and thereby cost
escalation.
• Therefore, an 85th percentile design speed is normally
adopted.
• This speed is defined as that speed which is greater than
the speed of 85% of drivers. In some countries this is as
high as 95 to 98 percentile speed.
204

205
Design SpeedDesign Speed
 Design speed is defined by the AASHTO Green
Book as: ...the maximum safe speed that
can be maintained over a specified
section of highway when conditions are
so favorable that the design features of
the highway govern.
 Design Speed should: 1) “…be consistent
with the speed the driver is likely to expect.”
and 2) “. . .fit the travel desires and habits of
nearly all drivers.”
 Not posted speed and not operating speed
(but ALWAYS higher than both)
 See first part of:
http://www.fhwa.dot.gov/environment/flex/c
h04.htm (Chapter 4 from FHWA’s Flexibility in
Highway Design)

206
Design Speed ConsiderationsDesign Speed Considerations
• Functional classification of the highway
• Character of the terrain
• Density and character of adjacent land
uses
• Traffic volumes expected to use the
highway
• Economic and environmental
considerations

207
Design Speed in Green BookDesign Speed in Green Book
(suggested minimum design speed)(suggested minimum design speed)
Rural Local Roads
Source: A Policy on Geometric
Design of Highways and Streets
(The Green Book). Washington, DC.
American Association of State
Highway and Transportation
Officials, 2001 4th
Ed.

208
Rural Collectors
Source: A Policy on Geometric
Design of Highways and Streets
(The Green Book). Washington, DC.
American Association of State
Highway and Transportation
Officials, 2001 4th
Ed.

209
Rural Arterials
 60 – 120 kph (40-75 mph)
 Depends on …
Terrain
Driver expectancy
Alignment (reconstruction)

210
Urban
• Locals 20-30 mph
• Collectors 30 mph+
• Arterials 30-60 mph

211
Values represent the
minimum acceptable
design speeds for the
various conditions of
terrain and traffic
volumes associated
with new or
reconstructed
highway facilities

212
InternationalInternational

213
Design TrafficDesign Traffic

214
Traffic DefinitionsTraffic Definitions
• Volume:
– number of vehicles, pedestrians, etc.
passing a point during a specific
period of time
– for vehicles, usually expressed as
veh/hour (vph) or veh/hour/lane
(vphpl)

215
• Demand:
– number of vehicles, pedestrians, etc. that desire to
travel between locations during a specific period
– Frequently higher than volume during certain peak
times
– Trips are diverted or not made when there are
constraints in the system
– difficult to measure actual demand because capacity
constrains the demand
• Capacity:
– maximum number of vehicles that can pass a point
during a specific period
– A characteristic of the roadway or facility

216
Characteristics of Traffic FlowCharacteristics of Traffic Flow
• Highly variable
– Time of day
– Day of week
– Season
– Road characteristics
– Direction

217
0
1000
2000
3000
4000
5000
6000
7000
12:30
A
M1:30
A
M2:30
A
M3:30
A
M4:30
A
M5:30
A
M6:30
A
M7:30
A
M8:30
A
M9:30
A
M10:30
A
M11:30
A
M12:30
PM1:30
PM2:30
PM3:30
PM4:30
PM5:30
PM6:30
PM7:30
PM8:30
PM9:30
PM10:30
PM11:30
PM12:30
A
M
Time of Day
Flowinvehiclesperhour
Highway Capacity
Highly Congested
Traffic Typically Peaks twice per dayTraffic Typically Peaks twice per day
Source: www.ecn.purdue.edu/~darcy

218
Volume StudiesVolume Studies
• AADT: Annual average daily traffic
(counted for 365 days)
• ADT: average daily traffic (counted
for > 1 day and < 365)
• PHV: peak hour volume
• Classification counts: fleet mix

219
Estimating AADTEstimating AADT
• Annual Average Daily Traffic
• Use count station information
• Extrapolate to non-count locations
• Used to adjust ADT for
– Seasons
– Daily variation

220
AADT Data Helps to:AADT Data Helps to:
• Estimate highway revenues
• Establish overall volume trends
• Establish annual accident rates
• Analyze benefits of road
improvements

221
Counting ProgramCounting Program
• To satisfy the traffic volume data
needs for all roads under a particular
jurisdiction, we establish a Counting
Program
A systematic pattern of counting
at different times and locations

222
Traffic Counts MapsTraffic Counts Maps
http://www.iowadotmaps.com/msp/traffic/index.html

223
Traffic Counts MapsTraffic Counts Maps

224
Design VolumeDesign Volume
• Usually hourly volume
• Which hour?
– Average hourly volume – inadequate design
– Maximum peak hour – not economical
– Hourly volume used for design should not be
exceeded very often or by very much
– Usually use 30th
highest hourly volume of the
year
– On rural roads 30 HHV is ~ 15% of ADT
– Tends to be constant year to year

225
Traffic DemandTraffic Demand
 Design Hourly Volume (DHV) – future
hourly volume (both directions) used
for design - typically 30th
HHV (highest
hourly volume) in the design year
 Why 30th
HHV?
 Breakpoint of 2-28
 Compromise: too high is wasteful, too
low poor operation
 Approximately median weekly peak hour
volume (top highest week peak hours)
(30th
HHV exceed 29 times in year)

226
Traffic Demand (cont.)Traffic Demand (cont.)
3. Exhibit 2-28 relationship between HHV and percent of
ADT in peak hour (referred to as K-factor)
Source: A Policy on
Geometric Design of
Highways and Streets
(The Green Book).
Washington, DC.
American Association of
State Highway and
Transportation Officials,
2001 4th
Ed.

227
Design Hourly VolumeDesign Hourly Volume
DHV is a representation of peak hour traffic,
usually for the future, or horizon year
K-factor represents proportion of AADT that
occurs in the 30th
HHV
K-factor = __DHV x 100
AADT
K = 8 to 12% urban, 12 to 18% rural

228
Design Hourly Volume (Example)Design Hourly Volume (Example)
If AADT is 3500 vpd and the 30th
highest hourly volume for the year is
420 vph what is the K-factor for that
facility?
K-factor = __DHV x 100
AADT
K-factor = __420 x 100 = 12
3500

229
Question: What’s the impact of choosingQuestion: What’s the impact of choosing
different K factor for design?different K factor for design?
If AADT is 3500 vpd, how will the design volume differ for K-
factor = 8% vs. 12%?
DHV = K-factor x AADT
100
DHVk=8% = 8 x 3500 = 280 vph
100
DHVk=12% = 12 x 3500 = 420 vph (diff of 140
100 veh)

230
• D = directional distribution = one
way volume in peak direction
(expressed as a percentage of two-
way traffic) Rural 55 to 80%
• Can also adjust for how traffic is
distributed between lanes (e.g., 3
lanes, highest/outside lane may be
40% of total directional flow)

231
Directional DistributionDirectional Distribution (example)(example)
If traffic is directionally split 60/40, what is directional distribution of
traffic for previous example (Design hourly volume = 420 veh/hr)?
Directional Design Hourly Volume (DDHV) =
0.6 x 420 = 252 veh/hr
Notice we use 0.6 not 0.4!!

232
• T = percentage of heavy vehicles during
design hour (Iowa interstate 35% plus)
• Affects capacity, ability to pass on two-
lane rural roads, etc.
• Larger, occupy more space
• Should determine % during design hour
(truck patterns may not be same as
passenger vehicles)

233
PHF = peak-hour volume
4(peak 15-min volume)
Flow is not uniform throughout an hour
HCM considers operating conditions
during most congested 15-minute
period of the hour to determine service
level for the hour as a whole
Peak Hour Factor (PHF)Peak Hour Factor (PHF)

234
Peak Hour FactorPeak Hour Factor

235
DHV = Peak-Hour Volume
PHF
Example
Peak hour volume from previous = 375
vph
PHF = 0.625
DHV = 375 = 600 vph
0.625
Note: the traffic you design for is the
busiest 15 minutes during the peak
hour … another way to think of it is 150
vehicles per 15 minutes = 600 vehicles
per 60 minutes

Design DriverDesign Driver
LECTURE 6LECTURE 6
237

238
CharacteristicsCharacteristics
• Design Driver: driver most expected
to use facility (familiar or
unfamiliar?)
– Accommodated in design, signing, etc.

239
Design Driver CharacteristicsDesign Driver Characteristics
Cont.Cont.
• Physical characteristics
• Processing ability
• Tolerable
Accelerations/Decelerations
– Longitudinal (along roadway )
– Lateral (around curves)
– Vertical (comfort)

240
Design Driver CharacteristicsDesign Driver Characteristics
Cont.Cont.
• Others?: age, gender, physical
condition (alcohol, etc.), mental
capabilities, skill (self perception – are
you in the top ½ of driver skill?)
• Two others related to design:
perception-reaction time and
expectancy

241
• Wide range of system users
• What range of drivers use the
system?
– Ages: 16 year old to 80 year old
– Different mental and physical states
– Physical (sight, hearing, etc)
– experience
• Design Driver: driver most expected
to use facility

242
0
2
4
6
8
10
12
PercentofDrivingPopulation
<20
20-24
25-29
30-34
35-39
40-44
45-49
50-54
55-59
60-64
65-69
70-74
75-79
80-84
>84
Age Groups

243
Visual AcuityVisual Acuity

244
Visual ReceptionVisual Reception
• Visual Acuity: Ability to see fine details
• Static (stationary objects):
–Depends on brightness
–Increases with increasing brightness
up to ~ 3 candles (cd/sq ft) --
remains constant after that
–Contrast
–Time (0.5 to 1.0 second)
• Dynamic (ability to detect moving
objects)
–Clear vision within a conical angle 3 to
5º
–Fairly clear within 10 to 12º
–Key criteria in determining
placement of traffic signs

245
• Peripheral Vision: Ability to see objects
beyond the cone of clearest vision (160
degrees)
– Age dependent
– Objects seen but details and color are not
clear

246
• Color Vision: Ability to differentiate
one color from another
– Lack of ability = color blindness
– Combinations to which the eye is the
most sensitive
• Black and white
• Black and yellow
y in determining traffic signs colors

247
• Depth perception
– Ability to estimate speed and distance
•Passing on two-lane roads
•Signs are standardized to aid in
perceiving distance

248
Hearing
Hearing perception
– Ability to detect warning sounds
– Sirens, horns

249
Perception/ReactionPerception/Reaction
TimeTime

250
Perception-Reaction ProcessPerception-Reaction Process
• Perception
• Identification
• Emotion
• Reaction (volition)
PIEV
Used for Signal Design and Braking Distance

251
Perception-Reaction ProcessPerception-Reaction Process
• Perception
– Sees or hears situation (sees deer)
• Identification
– Identify situation (realizes deer is in
road)
• Emotion
– Decides on course of action (swerve,
stop, change lanes, etc)
• Reaction (volition)
– Acts (time to start events in motion
but not actually do action)
• Foot begins to hit brake, not actual
deceleration

252
Typical Perception-Reaction
time range is:
0.5 to 7 seconds
Affected by a number of
factors.
What are they?

253
Perception-Reaction TimePerception-Reaction Time
FactorsFactors
• Environment:
• Urban vs. Rural
• Night vs. Day
• Wet vs. Dry
• Age
• Physical Condition:
• Fatigue
• Drugs/Alcohol
• Distractions

254
Perception-Reaction TimePerception-Reaction Time
FactorsFactors
• medical condition
• visual acuity
• ability to see (lighting conditions, presence
of fog, snow, etc)
• complexity of situation (more complex =
more time)
• complexity of necessary response
• expected versus unexpected situation
(traffic light turning red vs. dog darting
into road)

256
Perception Reaction Time (PRT)Perception Reaction Time (PRT)
• Time from Perception to Initial
Reaction to Stimulus (Example)

257
AgeAge
• Older drivers
– May perceive
something as
a hazard but
not act quickly
enough
– More difficulty
seeing,
hearing,
reacting
– Drive slower

258
AgeAge
• Younger drivers
– May be able to act quickly but not have
experience to recognize things as a hazard
or be able to decide what to do
– Drive faster
– Are unfamiliar with driving experience
– Are less apt to drive safely after a few
drinks
– Are easily distracted by conversation and
others inside the vehicle
– May be more likely to operate faulty
equipment
– Poorly developed risk perception
– Feel invincible, the "Superman Syndrome”
Human Factors - Perception and Reaction
by Joseph E. Badger. jebadger@harristechnical.com

259
AlcoholAlcohol
• Affects each person differently
• Slows reaction time
• Increases risk taking
• Dulls judgment
• Slows decision-making
• Presents peripheral vision
difficulties

260
ExperienceExperience
• Even NASCAR drivers practice
Familiarity
Faster on familiar
Unfamiliar more distracted
– Rental car on unfamiliar road at 10 pm when it starts
to rain (What is the driver doing?)

261
WeatherWeather
• Fog
• Rain
• Ice
• Snow
• affects ability to see (snow, fog)
• changes ability to stop (ice, snow,
wet)

262
UnderstandingUnderstanding
Flashing
DON’T
WALK

263
Count down
signal

265
• Most people do not reduce speed
in a work zone until they actually
see activity
• Only 78% of drivers in a study
understood what “Lane Ends”
mean
• Many people, especially older
drivers, don’t understand meaning
of left turn displays

266
FatigueFatigue
• Increases perception/reaction
time
• Study by American
Automobile Association found
that in 221 truck accidents
only 18.4% of the drivers had
been driving less than nine
hours.
• 41% of truck accidents

267
Dp
= 1.47(V)(t)
where:
Dp
= Distance traveled during PIEV
process (feet)
V = velocity (mph)
t = perception-reaction time = 2.5s

268
How much longer does it take an impaired driver to
perceive/react than an unimpaired one at 65 mph?
Unimpaired has P/R time of 2.5 seconds
Dp
= 1.47(V)(t) =
1.47(65 mph)(2.5 sec.) ~ 240 feet
Impaired Driver has P/R time of 4 seconds
Dp
= 1.47(65 mph)(4 sec) ~ 380 feet
Difference is 380 – 240 = 140 feet
Difference is safety and economic problem!
Example

269
Perception/ReactionPerception/Reaction
ApplicationsApplications
• Stopping sight distance
• Passing sight distance
• Placement of signs/traffic control
devices
• Design of horizontal/vertical curves

270
DriverDriver
ExpectancyExpectancy

271
Driver ExpectancyDriver Expectancy
• Expectancy (def) – an inclination based
on previous experience to respond in a
set manner to a roadway, traffic, or
information situation
• Types
– A Priori – long-term (based on
collective past experience) PRT =
0.6s avg., some 2.0s
– Ad Hoc – short-term (based on site-
specific practices/situations
encountered during a particular trip
on a particular roadway, PRT = 1.0s
avg., some 2.7s

272
Driver ExpectancyDriver Expectancy
• Driver Expectancies (what do we
expect as drivers?)
– Specific colors (red = stop)
– Driver ahead not to decelerate rapidly
– Slower drivers in left lane
– Work zone signs = people working
– Lane size
– Etc.

273
Selection ofSelection of

274
Design criteria must
be based on the
capabilities and
limitations of most
drivers and
pedestrians

275
The 85th
percentile is generally
used to select Design Criteria
The 95th
percentile or higher is
used where the consequences
of failure are severe
AASHTO recommends 2.6
seconds for stopping sight
distance (90th
)

276
RRole of Transportationole of Transportation
EngineerEngineer
• allow proper sight
distance in design,
sign placement
• avoid hitting driver
with too much info
at once
– one sign at a time
• clarity (sign size,
color, reflectivity)

277
Driver Activities in Selection ofDriver Activities in Selection of
PathPath
• Control (overt actions)
– Road Edge
– Avoid a Car
• Guidance (decisions)
– Lane Placement
– Car Following
– Passing

278
Driver Activities in Selection ofDriver Activities in Selection of
Path Cont.Path Cont.
• Navigation Level (planning)
– Maps
– Observe a directional sign

Sight DistancesSight Distances
279

280
Important Sight DistancesImportant Sight Distances
1. Stopping
2. Decision
3. Passing
4. Intersection
5. Crossing RR
FIRST AND THIRD WILL BE DISCUSSED
HERE

281
Sight Distance in DesignSight Distance in Design
• For safety, should provide sight distance
of sufficient length so that drivers can
control the operation of their vehicles to
avoid striking an unexpected object in the
traveled way - STOPPING SIGHT
DISTANCE (SSD)
• Certain 2-lane roads should have sufficient
sight distance to enable drivers to occupy
the opposing traffic lane for passing other
vehicles without risk of crash - PASSING
SIGHT DISTANCE (PSD)

282
Green Book (AASHTO)Green Book (AASHTO)
Policy QuestionPolicy Question
• Sight distance assumes drivers are
traveling at:
– A. The posted speed limit
– B. 10 mph above the speed limit
– C. The 85% percentile spot speed of
the facility
– D. The design speed of the facility

283
Design Policy - ResponseDesign Policy - Response
• Sight distance assumes drivers are
traveling at:
– A. The posted speed limit
– B. 10 mph above the speed limit
– C. The 85% percentile spot speed of
the facility
– D. The design speed of the facility

284
GB Question with responseGB Question with response
• Stopping sight distance is composed
of two distances, what are they?
– Distance traveled during
perception/reaction time
– Distance required to physically brake
vehicle

285
Studies onStudies on
Perception/Reaction TimePerception/Reaction Time
• 321 drivers (Johansson and Ruma):
drivers expected to use brakes
– Median: 0.66 sec
– 90th
percentile: >= 1.5 sec
• Unexpected, response time increased by ~
1 sec
• Some drivers took over 3.5 seconds to
respond even under simple test condition

286
GB QuestionGB Question
• AASHTO GB recommends 2.5
seconds, this is adequate for
conditions that are more complex
than the simple conditions used in
laboratory and road tests.

287
Sight distanceSight distance
Distance a driver can see ahead at
any specific time Must allow
sufficient distance for a driver to
perceive/react and stop, swerve etc
when necessary

288
Stopping Sight DistanceStopping Sight Distance
(SSD)(SSD)
 Required for every point
along alignment
(horizontal and vertical) –
Design for it, or sign for
lower, safe speed
 Available SSD =
f(roadway alignment,
objects off the alignment,
object on road height
 SSD = PRT + BD (with
final velocity V2
= 0)

289
Criteria for Sight DistanceCriteria for Sight Distance
• Driver eye height: for passenger
vehicle’s = 3.5 ft above surface
• Height of object in roadway = 2 feet
(SSD)
• Height of opposing vehicle = 3.5 feet
(PSD)

290
Deceleration rate: AASHTO: 11.2 ft/s2
Deceleration is within capability of drivers
to stay within their lane and control the
vehicle when braking on wet surfaces and
is comfortable for most drivers
• AASHTO represents friction as a/g
which is a function of the roadway, tires,
etc
• Can use when deceleration is known
(usually not)

291
BD = V2
30[ (a) ± G]
(g)
Where:
BD = braking distance (ft)
V = speed (mph) (can also be “u”)
a = deceleration rate (ft/s2
)
G = grade (decimal)
g = acceleration due to gravity =32.2 ft/s2

292
Braking DistanceBraking Distance
Assumes a rate of deceleration, driver may brake harder
a = 11.2 ft/sec2
normal
a = 14.8 ft/sec2
emergency, use tables from AASHTO
Friction is a function of pavement condition (wet, icy), tire,
and roadway surface
Depends on weight, but some assumptions are made to
arrive at a standard equation

293
SSD EquationSSD Equation
SSD = 1.47ut + _____u2
_____
30({a/g} ± G)
SSD in feet
u speed in mph (may also see “v”)
t perception/reaction time (in seconds)
a assumed deceleration rate (ft/sec2
)
g gravitational force (32.2 ft /sec2
)
G gradient in ft/ft

294
SSD ExampleSSD Example
Use basic assumptions to determine SSD at 60 mph on
a) 0% grade, b) 3% grade
SSD = 1.47u(2.5 sec) + ________u2
________
30({11.2/32.2} + 0.00)
SSD = 220.5 + 345.5 = 556 ft
(compare to table 3-1 in GB – See next slide)
On a +3% grade, SSD = 220 +318 = 538 ft

295
Stopping
(emergency) –
SSD (Table 3-1)
Source: A Policy on Geometric Design of
Highways and Streets (The Green Book).
Washington, DC. American Association of
State Highway and Transportation Officials,
2001 4th
Ed.

296
SSD ExampleSSD Example
Given: Available Sight distance = 430’ on a +3% grade
Find maximum speed if perception reaction time is assumed to be 2.5
seconds
430 feet = 1.47u(2.5 sec) + ________u2
________
30({11.2/32.2} + 0.03)
430 feet = 3.68u + ________u2
________
30(0.378)
Solving for u, u = 52.0 mph (Set speed at 50
mph)
Discuss: Would this be an acceptable condition if
the road is generally posted for 60 mph?

297
ExampleExample
Consider analysis when vehicle skids
across different surfaces (a/g is not
equal to 0.35)
Or final velocity is not zero at the end of
the skid, as evidenced because the
vehicle sustains crushing damage until
the vehicle is stopped.

298
where:
terms are as before, except
vo = original velocity
vf = final velocity at impact
With assumed acceleration, using friction
S = PRD + Db
= 1.47vot + vo2
- vf2
30(f ± G)

299
ExampleExample
Accident Reconstruction:
Average Skid Mark = 47 feet
Crush damage indicates 20 to 30 mph speed at impact
f = 0.65 (how do they know this?), level roadway, and 40 mph posted
speed.
Was vehicle speeding?
47 feet skid represents what? BD?
If final speed is 30 mph …
BD = 47 = (Vi
2
– 302
)/30(0.65 + 0)
Vi
= 42.6 mph
If final speed is 20 mph (Vi
= 36.3 mph)
What if pavement changes to gravel after 47 feet and car slides
another 30 feet (f = 0.7)? What is initial speed?

300
Typical values for frictionTypical values for friction
Values of friction vary widely with road
surface type, age, condition. Examples:
Surface type f (or a/g)
Concrete pavement -dry 0.60 to .75
Concrete pavement – wet 0.45 to .65
Asphalt pavement 0.55 to .70
Gravel 0.40 to .70
Ice 0.05 to .20
Snow 0.30 to .60
Source: Lynn Fricke, Northwestern Univ.

301
Decision Sight DistanceDecision Sight Distance
• SSD are sufficient to allow reasonably
competent and alert drivers to come to a
hurried stop under ordinary circumstances
• May be inadequate when drivers must
make complex or instantaneous decisions,
when information is difficult to perceive or
when unexpected or unusual maneuvers
are required
• Equations in book, use tables

302
Decision Sight DistanceDecision Sight Distance
• When situation is unexpected or
driver must make unusual maneuvers
or under difficult-to-perceive
situations
• Requires higher P/R time
• Depends on type of maneuver
made and roadway setting (urban vs.
rural)
• Use table 3.5 from Text, page 75

303
Decision
(controlled stop, speed/path/route change) – DSD (Table 3-3)
Source: A
Policy on
Geometric
Design of
Highways and
Streets (The
Green Book).
Washington,
DC. American
Association of
State Highway
and
Transportation
Officials, 2001
4th
Ed.

304
Passing Sight DistancePassing Sight Distance
Assumptions (conservative?):
1. Vehicle being passed travels at uniform speed
2. Speed of passing vehicle is reduced behind passed
vehicle as it reaches passing section
3. Time elapses as driver reaches decision to pass
4. Passing vehicle accelerates during the passing
maneuver and velocity of the passing vehicle is 10
mph greater than that of the passed vehicle
5. Enough distance is allowed between passing and
oncoming vehicle when the passing vehicle returns
to its lane

305
Source: A
Policy on
Geometric
Design of
Highways and
Streets (The
Green Book).
Washington,
DC. American
Association of
State Highway
and
Transportation
Officials, 2001
4th
Ed.

306
Dpassing = d1 + d2 + d3 + d4
d1 = distance traveled during P/R time to point where
vehicle just enters the left lane
d1 = 1.47t1(u – m + at1)
2
where
t1 = time for initial maneuver (sec)
u = average speed of passing vehicle (mph)
a = acceleration (mph/s)
m = difference between speeds of passing and
passed vehicle

307
d2 = distance traveled by vehicle while in left lane
d2 = 1.47ut2
where:
u = speed of passing vehicle (mph)
t2 = time spent passing in left lane (sec)

308
d3 = clearance distance varies from 110 to 300 feet
d4 = distance traveled by opposing vehicle during passing
maneuver
d4 usually taken as 2/3 d2

309
Important Sight DistancesImportant Sight Distances
(cont.)(cont.)
4. Intersection (turning/crossing)
5. Crossing RR
1. Stop, proceed, proceed from stop

310
• Crossing
RR
• Stop,
proceed,
proceed
from stop

311
What are the key
variables?

312
Key issues in safe crossingKey issues in safe crossing
Speeds
D Distance from front of vehicle to driver’s eye
Dt Distance from rail to front of vehicle
Vv Assumptions about PR time and braking distance
W Width of crossing
D Distance from end of vehicle after crossing
L Length of vehicle
Acceleration capability of road vehicle
Offset of obstruction from the road and the rail line

313
HomeworkHomework
Go to the example on slide 24. Calculate the vehicle
speed if the roadway is gravel.
Next calculate the vehicle speed on the paved roadway,
but with snow and ice on the road (f = 0.30).
Show your work and discuss how much a driver should
reduce his/her speed for ice and snow on the paved road.

Highway And traffic Engineering

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