0 CNote - 351 Combined 2011
0 CNote - 351 Combined 2011
0 CNote - 351 Combined 2011
ON
BY
PRF. DR. MD. SHAMSUL HOQUE
Syllabus
Traffic engineering:
The road/traffic system,
Vehicle and traffic characteristics;
Traffic control devices;
Traffic studies;
Parking; Roadway lighting; and
Terminals.
Class Distribution
Class 1 Introduction
Class 2 Traffic Engineering
Class 2&3 The Road/traffic System
Class 3&4 Vehicle and Traffic Characteristics
Class 5, 6, & 7 Traffic Studies
Class Test 1
Class Test 2
Class 12 Lighting
Class 13 Terminals
Class 14 Overview
Kadiyali, L.R.,
Traffic Engineering and Transport Planning, Second Edition, 1983.
Singh, G. C.,
Highway Engineering, Third Edition, 1991.
OFlaherty, C.A.,
Highways and Traffic, Volume 1, Second Edition, 1983.
Main Objectives
Control of trip demands
Distribution of peak periods
Encouraging public, bicycle and walking modes
Modern Trend
Planning & policies
Integrated land use and transport planning
Modular city & zonal concept (self-contained)
Multipurpose usage of same r.o.w
Segregated Public transport facilities (Automatic People Mover)
Integrated walking and bike facilities
Restricting private modes
IT based communication backbone coupled with smart policies viz. paper less administration/services, place
independent jobs, virtual shopping, e-bank, e-commerce, distant education system etc.
Construction
Built Operate and Transfer (BOT) concept
Auto soil compaction
Use of Modified binder
Recycling
Intelligent Transport System (ITS)
Smart Road
Magnetic vehicle track
Equipped with roadside/embedded/gantry - fiber optics, sensors, detectors, beckon, VMS, CCTV, etc.
Smart Vehicle
Built-in telematics
Built-in safety features
Auto emergency phone
Built-in theft proof feature
Renewable fuel (echo friendly vehicle)
Public Transport
Driver-less, demand responsive, non-stop, fast, smart payment
Interactive passenger information system
Traffic Control & Management
Dynamic drivers & passengers information system
Demand responsive & adaptive traffic control system
Auto toll/Congestion pricing (virtual toll plaza: smart card & transponder)
Auto surveillance
Dynamic fleet management system
Definition
Traffic engineering is the science of
measuring traffic and travel, the study of basic laws relating to traffic flow and generation, and
application of this knowledge to the professional practice of planning, designing, and operating traffic systems to
achieve safe, efficient and convenient movement of persons and goods.
History
Traffic Engineering as it is known today has evolved gradually with increase in traffic (veh.& ped.)
Initially it was limited to application of simple rules and regulations such as left driving rule, road signs, marking,
and intersection control by flag etc.
Subsequent analysis of traffic operations and road accidents led to the realization the traffic regulations and other
methods of traffic control should be based on proper engineering studies.
In consequence as extension of traffic regulations - many new traffic control and management techniques were
devised viz. speed zoning, traffic signals, turn restrictions, parking restrictions, bus priorities, one-way street etc.
Eventually it become evident that the planning and design of efficient road network largely depends upon the
integrated land-use & transport policies and effective demand management (road pricing to control & distribution
peak hours)
Modern traffic engineering measures are mostly restrictive and dynamic in nature and largely depend on public
transport facilities and information technology (IT).
Objectives
to improve overall roadway capacity
to ensure safety
since both vehicle-vehicle and vehicle-pedestrian conflicts reduce roadway capacity and cause accident risk
overall objective is to minimize these conflicts so as to make the most economic use of the existing roadway
facilities
Introduction
The Road-Traffic system is a complex interaction among four components -
Road
Vehicles
Road users
Environment
ROAD
It comprises as follows:
Links
Intersections
Footpath/Shoulder
Fly-over/Tunnel
Foot over/under bridge
Bus lay-by/Terminal areas
Parking areas
Loading/unloading areas
Channel/islands/medians etc.
Road bridges/culverts
Traffic control devices
Roadway types
A. Geographical area or location-wise
Rural Road
Urban Road
B. Function-wise
Rural Road
National Highways
Regional Highways
Feeder Road A
Feeder Road B
Urban Road
Primary/Main/Arterial Road
Secondary Road
Local Road
C. Standard-wise
Full access control, Expressway/Motorway, with grade separated junctions
Partial/No access control with at-grade intersection
D. Usage-wise
Commuter road
All purpose road
By-pass
Distributor/Ring road
Feeder/Collector road
Slip/access road
Service road
Frontage road
E. Operation-wise
Single Carriageway/Undivided Road
Dual Carriageway/Divided Road
Two way
One-way
Lane/non-lane based
F. Investment-wise
Public Road - Free
Private: Build, Operate and Transfer (BOT) tolled road
VEHICLES
Types of Vehicle
Propulsion force wise
Motorized
Truck
Large
Single
Articulated
Trailer
Semi-trailer
Small
Mini/Pickup
Bus
Large
Single-deck
Double-deck
Mini
Micro
Car/Jeep etc.
Motorcycles
Other non-conventional
Non-motorized
Rickshaw
Bicycle
Other non-conventional (animal driven)
Service/usage-wise
Private
Public
Mass transit bus, tempo, tram, trolley buses, Light rail transit (LRT) etc.: use shared carriageway
Rapid transit underground rail/metro/tube, elevated guide-way, LRT system etc.: use segregated
carriageway
Personalized transit
Para-transit - rickshaw, auto rickshaw
Taxi service
Rent-a-Car/hired car
Carrier-wise
Passenger vehicles
Freight vehicles
ROAD USERS
Comprises:
Drivers
Passengers
Pedestrians
ROADWAY ENVIRONMENT
Include elements which influence traffic operating condition:
Roadway geometric conditions standard of road, surface condition, horizontal & vertical alignment
Traffic control & regulation
Road side management pedestrian/parking/access control
Lighting condition
Flaring
Slip Road
Median lane
Footpath
Mixed Lane
Corner
Widening
E x it Pedestrian
Crossing
Bus
Lay-by
Approach
Approach Exit
Link/
Mid-Block
Approach
Approach
Unchannelized Y Channelized Y
3 - LEG INTERSECTIONS
4 - LEG INTERSECTIONS
STAGGERED INTERSECTIONS
Multileg Rotary/Roundabout
Central Island
Weaving
movement
Intersection Leg
E x it
ROTARY/ROUNDABOUT
DIVERGING
MERGING
CROSSING
Vehicular Characteristics
It would be impracticable and uneconomical if roadway is designed to accommodate all types of vehicles.
Generally, roadway is design for design vehicle that will enjoy safe driving and full level of service (LOS)
whereas, extreme users will get lower safety and LOS.
A vehicle that represents the design standards is termed as design vehicle. Whose properties are fixed based
on statistical analysis of population 50th percentile (mean) value; 85th percentile or maximum value etc.
depending on the purpose of use i.e. fixing turning path, parking lot design etc. Characteristics of design vehicle
actually fix all the dimensions of the road.
The various vehicular characteristics affecting the road design can be classified as
Static characteristics and
Dynamic characteristics.
Static/physical Characteristics
Axle load - Weight of vehicle affects
structural design of
pavement number of layers, thickness of each layer, material requirements etc.
bridge/fly-over/grade separator
fixing gradient of roads in rolling terrain, ramp, bridge approach etc. and it is depend on vehicles
weight/power ratio
Width - Width of Vehicle affects
lane width
shoulder width
width of parking bay
Length - Length of vehicle affects
design of horizontal alignment i.e. determination of extra widening and minimum turning radius
passing sight distance
parking facility (bay & isle)
roadway capacity
Height - Height of vehicle affects
clearance to be provided under the structures e.g. under-bridge, over-bridge, sign-post gantry, electric
services lines, etc.
Dynamic Characteristics
Speed - It is such a factor that controls most of the geometric standards of the highway viz.
horizontal and vertical alignment design
limiting radius
grade
length of transition curve
super-elevation
stopping/overtaking sight distance
width of pavement on straight and curves
capacity/LOS
intersection design and control (fixing amber period, co-ordinated signal design, stop sign, etc. )
skid resistance
Acceleration/Deceleration (braking) performance
acceleration capability influences junction capacity, safe passing distance etc.
maximum deceleration rate is required to know safe stopping distance
Driver Characteristics
Drivers characteristics are involved in
accommodating roadway environment during driving or adopting safe speed according to roadway environment:
curved/straight
poor surface condition
lane width
poor access controlled
density of traffic
approaching towards priority junction
negotiating bottlenecks: intersections, speed breakers, bridges, pedestrian crossing, side roads,
day/night, weather condition: sunny/foggy/rainy
gap acceptance
lane change/overtaking
crossing junction at the end of green period (stopping/not stopping)
keeping headway with the leader
roadway sign design (letter height/size and placement color perception, depth of vision, speed)
street lighting design (fixing level of illumination depending on drivers ability to see)
roadway markings design (color and intensity of retro-reflective markings)
licensing control
Reaction Time
The time interval between seeing, hearing, or feeling, and the starting to do something in response to the stimulus of a traffic
or highway situation is called reaction time. Ideally, this response of the driver requires time for the following psychological
process:
Perception - which involves seeing the stimuli along with other perceived objects
Identification or intellection - which involves the identification and understanding of the stimuli
However, this sequence does not typically occur in emergency/ surprised situations. Rather, perception of a dangerous
situation is frequently followed by emotional response without the intervening stage of intellection. As this emotional
response is very quick and sudden almost reflex-like, often provides undesirable/disorganized response in the face of a
hazardous situation.
PIEV
The total time required to perceive and complete a reaction to a stimulus is the sum of the times necessary for
perception, identification, emotion, and violation. This total reaction time is often referred to as the PIEV time.
The time required for reacting properly and safely (after making proper evaluation of all pertaining factors) can
vary from about 0.5 sec for simple situations to as much as 3 or 4 sec for more complex situations.
PIEV time is required to determine
safe-stopping sight distance
safe approach speeds at intersection
amber/clearance time interval for traffic signals
PIEV time increases with
complexity of situation
gravity of the event (people generally react quicker to very strong stimuli than to weak ones)
vehicle speed
drivers age
physical deficiencies
mental/emotional state/psychological conditions which temporary distract attention/
concentration/alertness of driving or make less responsive to stimuli:
Besides above factors PIEV time depends on
speed of vehicle
even location of roads etc. within built-up drivers remain extra vigilant/alert and always expect surprise
situation, in contrast driving in open rural highway is very relaxed and less attentive
PIEV design value
design value is usually based upon the normal range of road users (85th percentile group) and not upon the
abnormal. (design would be uneconomical if extreme values are considered)
brake reaction time recommended by AASHTO for (perception time = 1.5 sec)
rural area 1.0 sec (PIEV = 2.5 sec)
urban area - 0.75 or 1.0 sec (PIEV = 2.25 2.5 sec)
Pedestrian Characteristics
General
important especially in urban areas
pedestrian actions are less predictable than those of drivers as many pedestrians consider themselves outside
the law in traffic matters
they are hard to enforce
pedestrians are more often disobey traffic control devices than are drivers
Crossing Characteristics
in generally pedestrians tends to walk in a path that represents the shortest distance or most convenient route
between two points
they often cross at mid-block instead of using crosswalks
pedestrians also have a basic resistance to change grades when crossing roadways
they dont voluntarily make use of special pedestrian facilities such as underpasses or overpasses
References
Institute of Traffic Engineers, Traffic Engineering Handbook, Third Edition, 1965.
Institute of Traffic Engineers, Transportation and Traffic Engineering Handbook, Second Edition.
Matson, M.T. and Hurd, W.F., Traffic Engineering, McGraw-Hill, 1955.
Kadiyali, L.R., Traffic Engineering and Transport Planning, Second Edition, 1983.
Planning and designing traffic facilities, including the selection of geometric standards, economic analysis, and the
determination of priorities
Determining the need for traffic control devices such as signs, traffic signals, pavement markings, school &
pedestrian crossings
Studying the effectiveness of introduced schemes
Diagnosing given situations & finding appropriate solutions
Forecasting the effects of projected strategies
Calibrating and validating traffic models.
Traffic surveys are the means of obtaining information for these purposes. Specifically, the main purposes of traffic surveys
may be summarized as follows:
Traffic Monitoring
Traffic Control and Management
Traffic Enforcement
Traffic Forecasting
Model Calibration and Validation
Much of the data collected is used to define the limiting parameters and modal values. Since the amount of data
involved is large statistical methods are widely used to reduce the task.
References
Definitions
Volume/flow
The total number of vehicles that pass over a given point or section of a lane or roadway during a given time interval.
It may be expressed in terms of annual, daily, hourly, or sub-hourly periods; usually in vph or vpd. Volume is an actual
number of vehicles observed or predicted to passing a point during a given interval.
Rate of flow
The equivalent hourly rate at which vehicles pass over a given point or section of a lane or roadway during a given
time interval less than 1 hr. usually 15 min. It represents the number of vehicles passing during a time interval less
than 1 hr, but expressed as an equivalent hourly rate.
Objectives
The purposes for carrying out traffic volume count are as follows:
Design purposes
structural and geometric design of pavements, bridge, and other highway facilities
intersection design including minimum turning path, channelization, flaring, traffic control devices viz. traffic signs,
markings, signals based on approach volume and turning proportions
pedestrian volume study is useful for designing side walks, pedestrian crossing etc.
Improvement purposes
to allocate limited maintenance budget rationally it is important to know the traffic volume carried by a particular
roadway section in order to decide the importance of the road and fixing its relative priority
in order to improve the roadway operating condition it is important to know the traffic volume
to examine the existing operating/service condition of a roadway section
to check the need for (warrant) traffic control devices
to determine the type of improvement measure need to be taken
to measure the effectiveness of a traffic control measure
Other Purposes
estimation of highway use
measurement of current demand of a facility
estimation of trends
economic feasibility evaluation
computation of accident rates - accidents/100m vehicle-miles
Types of Flow/Volume
Methods of Counting
Manual Counting Method following are the most common forms of manual counting methods:
Direct Method - data is collected by using hand tally and manual counters/enumerators
Advantages
besides traffic volume, vehicle classification and turning proportions can be obtained
data can be use immediately after collection
Disadvantages
not practicable for long duration count and when flow is high
counts become error prone specially when volume is high
no scope for cross check
weather susceptible
Automatic Counting Method following are the most common forms of auto counting techniques:
Contact system - viz tube, loop, piezo detectors/sensors
based on pneumatic action
based on mechanical actuation
based on magnetic actuation
based on piezo-electric actuation
Contact-less system
based on electrical/optical actuation by interruption of a light beam falling on a photoelectric cell as vehicle
passes
radar devices based on Doppler principle (phase shift of the reflected energy)
ultra sound imaging
infra red imaging (sensing heat-radiation)
based on two-way micro-wave communication between vehicle (Electronic Tag/Smart Card) & counting
station
based on CCTV/video image processing machine vision technique (pattern recognition)
Advantages
suitable for long duration/continuous counts
useful for permanent counting station
able to get data in usable format (no need of data entry) & on line data collection facility
less expensive
weather friendly
no street surface dug up (unlike loop) is required for contact-less methods; they are installed at or above the
road surface level
Disadvantages
most of the methods required strict lane discipline
difficult to detect non-motorized vehicles specially using the contact based detectors
can classify only few distinct classes of vehicle (with increase in vehicle classes calibration/auto-recognition
process become more error prone)
data is not as accurate as that from manual method (required comprehensive & routine calibration)
usually do not provide directional count (as detection become difficult)
installation and maintenance costs are high; needed over-head gantry or road side tower
Counting Periods
The count can be for any duration and depends on the objective of the study or the information needed. Generally:
Short duration count at peak periods is conducted for operational studies including those for roadway improvement
& maintenance and traffic control & management
Long duration count is conducted for transport planning and design
References
Institute of Traffic Engineers, Transportation and Traffic Engineering Handbook, Second Edition.
OFlaherty, C.A., Highways and Traffic, Volume 1, Second Edition, 1983.
Transportation Research Board, Highway Capacity Manual, Special Report 209, Third Edition, 1994.
If traffic data are collected continuously for a long period and presented for a number of consecutive
days, weeks, months, years etc. then the repetitive nature of the variation will be observed, since the
pattern of the hourly, weekly, monthly variations will be similar for all years, although the actual
volumes may not necessary be the same.
There are two approaches for the estimation of ADT, AADT from short counts:
1. Factor approach - previously established expansion factors from continuous count are used.
2. Regression approach
Factor Approach:
total 24-hr vol.
a. Hourly expansion factors, HEF =
vol. for particular hr.
These factors are used to expand counts of durations shorter than 24 hr. to 24-hr vol.
Thses factors are used to determine weekly vol. from counts of 24-hr duration.
AADT
c. Monthly expansion factors, MEF =
ADT for particular month
These factors are used to determine AADT from the ADT for a given month.
Problem:
A traffic engineer urgently needs to determine AADT on a rural primary road that
has the volume distribution characteristics shown in Tables 1, 2 & 3. The
engineer collected data shown below on a Tuesday during the month of May.
Determine the AADT of the road.
Hour Volume
7:00-8:00 a.m. 400
8:00-9:00 a.m. 535
9:00-10:00 a.m. 650
10:00-11:00 a.m. 710
11:00-12:00 p.m. 650
* Estimate the 24-hr vol. for Tuesday using the factors given in Table 1:
* Adjust the 24-hr volume for Tuesday to an average volume for the week using
the factors given in Table 2:
* Since the data were collected in May use the factor shown in Table 3 to obtain
the AADT:
Definition
Speed The rate of movement of a vehicle, generally expressed in fps, kph or mph.
Objectives
The main objectives of speed studies are:
Capacity studies
Geometric design
Accident analysis
Economic studies
Performance study of a traffic control measures (before & after studies)
Planning and designing traffic control measures viz:
Traffic signal design
Designing road signs
Designing parking crossings
Establishing speed limits
Speed zoning
Placing speed breaker etc.
Types of Speeds
Time-mean speed : The speed obtained when the sum of all values is divided by the number of observation. It gives
arithmetic mean of the spot speeds vehicles passing a point. Useful for traffic regulation purposes.
_ vt
vt
n where: vt = individual speeds
n = no. of observation
Space-mean speed : The speed obtained when speeds are averages over space. It gives the harmonic mean of the
speeds of vehicles passing a point, on a highway, during an interval. Useful for establishing speed-flow relationship.
_
n ns
Vs _
1 / v t
t
where: s = space distance
t = mean travel time.
Example
The following travel times were observed for 4 vehicles traversing a 1 mile segment of highway:
Vehicle Time (min)
1 1.6
2 1.2
3 1.5
4 1.7
Calculate the space and time mean speeds of the vehicles.
Problem
Following data was collected while conducting spot speed studies at certain stretch of a road within the urban area.
Determine:
average speed of traffic stream
modal speed and pace of the traffic stream.
upper and lower values of speed limits for regulation
design speed for checking the geometric design
Solution:
Sd = sqrt[S12/n1 + S22/n2]
= sqrt[7.5^2/250 + 7.4^2/280]
= 0.65 mph
Zcritical = 1.96 at 95%confidence level
Introduction
It is a modified form of the speed study
It measures the average journey time
Objectives
To find out the locations, causes and duration of the delay/congestion
To prescribe the remedied measures of congestion
To assess the quality/efficiency of road network
For economic evaluation of improvement measures
To evaluate the performance of particular measure
For travel demand management/route guidance
Causes of Delay
Fixed/Geometric delay Delay incurred due to roadway geometry. It occurs mainly due to road intersections/
signals, narrow road/bridges, sharp horizontal and vertical curves etc. It is unavoidable and almost same for all
vehicles.
Operational delay It is mainly caused by road-side and inter-vehicular frictions such as:
road side parking
road side non-motor activities
road side pedestrians movements and random crossings
bus stoppage near intersections
high traffic volume and lack of roadway capacity
merging, turning, lane changing/overtaking or weaving maneuvers etc.
Traffic engineers are interested about the operational delay which is fluctuating in nature and controllable.
Delay/Congestion
Indicates the situation when extra time is needed to travel through a roadway facility.
Types of Delay/Congestion
Non-recurrent Delay: which is unpredictable in nature and occurs due to the following random events:
flow break down at peak periods (make shock wave - which quickly amplify and propagate to down stream)
accidents
special events (sports, national events etc.)
signal malfunction etc.
Recurrent Delay: which occurs periodically at particular locations and particular time of a day.
daily morning/evening peak periods congestion due to rush commuter movements
congestion other than the peak periods on all purposes roads due to increased flow level
Presentation of results
Speed and delay data may be presented in tabular or graphical form to show speeds and speed variation profiles
along the route being studied together with the locations, causes and duration of delays.
Introduction
Traffic volume counts give the amount of traffic passing at specified locations on the road but they do not indicate
where traffic desires to travel i.e. its origin and its destination.
An origin and destination survey is designed to obtain such information about the movements of vehicles and
passengers within an area.
Objectives
To know the terminal points of a trips, direction of travel, selection of routes and trip lengths
For transportation planning, design and operation of road-network and terminals (particularly the location, design
and programming new or improving highways, by-pass, terminals, regulations etc.).
For planning and designing public transport and parking facilities etc.
For economic evaluation of alternative plans.
Presentation of results
The results are usually expressed in the form of desire-line-graphs - which represent trip nos. between zone of
origin to destination. The greater the band thickness the greater being the number of trips. The desire lines density
easily reflects the necessity of new links, diversions, by-passes, regulations etc.
Introduction
Parking studies mainly for car
Usually conducted for urban areas with high demand for parking
Parking is essential for business & commercial activities
It should be an integral part of roadway system and provision of off-street parking spaces should be considered at
the urban planning stage
It is roughly estimated that out of 8,760 hours in a year, the car runs on an average for only 400 hours (4.5%),
leaving 8,360 hours when it is parked.
Parking control has potential to improve roadway capacity and safety
Introduction
Traffic control devices include all
signs
markings
signals
Objectives
to regulate
to warn
to guide traffic movements and thereby
to ensure safe and smooth flow of traffic movements
General requirements
Traffic control devices should:
fulfill a need must be reasonable and appropriate for the traffic requirements at the locations used
command attention & respect of drivers and pedestrians must not be used where it is not warranted;
otherwise it will invite drivers to disregard and to have less respect for traffic control devices in general
convey a clear, simple meaning - legible at long range and understandable at a glance
be place so as to give users time for proper response
be uniform in design and application the size, shape, color of the device/letter/symbol, mounting height, siting
and lighting should be uniform and consistent
be visible both at day & night
be maintained at high standard - to ensure legibility and visibility
generally as some control devices impose restriction on vehicle movements it is recommended that
these should be use conservatively to avoided disrespect by the drivers if used in excess, tend to lose
their effectiveness.
moreover, these should not be used alone, where enforcement is required to compel drivers to obey them.
Introduction
Traffic signs are mainly used to
inform drivers about regulations
adjust their lane position, speed
guide them to reach their points of interest
Classification
Functional classes of traffic signs are:
Mandatory Signs (shall follow)
inform users of traffic laws or regulations
the violation of these signs is a legal offence
these are usually circular in shape with red border, white background
Examples
Regulatory
slow/slop
keep right
restriction on speed, size, weight
one way traffic etc.
Prohibitory
no right/left/U turn
no entry for vehicle types
no overtaking
no horn
no waiting/parking etc.
Special mandatory signs for priority typed intersections
STOP
used when vision is obstructed
USA/UK practice octagonal, red background, white border
YIELD/GIVE WAY
used when vision is not obstructed and stop is needed only when necessary
USA/UK practice triangular pointing down ward
Warning or Cautionary Signs (should follow)
These are known as safety signs
Not always an offense if not complied with
Usually equilateral triangle or diamond in shape
These signs convey message to warn about potentially hazardous conditions ahead and where some
caution/attention is required for examples:
side road
junctions
level crossing
zigzag/slippery road
sharp bend
road hump
narrow bridge
school, hospital, cinema hall etc.
Informatory or Guide Signs (may follow)
These signs show the direction of important places of interests and are used to guide road users along route
to make the travel convenient, safe and comfortable
Used at a location where the motorist would be in doubt
Informatory signs do not lose their effectiveness by over-use and as such it is desirable to use them as
frequent as is necessary
Usually rectangular in shape
Examples
route direction
points of interests
mile stone/distance
Height of Signs
Post height is measured from the pavement surface
open area 1.5m
built-up area 2.1m
Size of Lettering
Should be such that they can be easily read when vehicles are moving
USA practice size is related to type of highway
UK practice based on empirical formula
New Trend
increasing use of icons, logos and symbols instead of using letters and words
increasing use of Variable Message Signs (VMS)
VMS:
Conventional signs are very rigid in the sense that they carry fixed and limited information for all road-traffic
environments. Whereas, VMS display-panels are used to display real time traffic information. Capable of
displaying graphics and/or alphanumeric messages. They are more responsive to the field conditions. Need
electricity and data communication facilities.
Bangladesh
absence of complete "Highway Manual"
faulty designs (inconsistent size, color, wording, incorrect height, placement etc.)
absence of required signs at potentially hazardous locations
misuse of signs,
obstructed signs
poor maintenance
existence of misguiding signs
lack of supplementary markings
presence of a large number of illiterate road users
eventually all these above factors contributed to lost the respect & effectiveness of traffic signs as controlling
device and in consequence, with time a tendency has developed among the road users to ignore the signs
as power failure is very common, use of retro-reflective signs/markings would be most appropriate even within the
city areas
Introduction
Road marking are used as a means of controlling and guiding traffic
They promote road safety and bring about smooth flow of traffic
Markings consist of paint on the pavement and curb to convey traffic regulations and warnings to drivers
Markings may be used alone or in combination with traffic signs or signals
Markings Materials
Paint - thermoplastic cement paint (non-reflective/reflective)
Self-adhesive plastic/aluminum sheet
Studs (raised marking)
Glass beads are used to produce retro-reflective/cats-eyes effects of the markings - to aid night driving especially
in rural open areas.
New Trend
Conventional road markings are effective only at dry weather not during rainy condition as rain water cover the
markings and hinder reflection. New type of highly durable plastic retro-reflective material is being used in 4mm
thick layer to give lane markings which is visible even during wet (usually 2mm rain water film) condition - it is less
expensive than that of cats-eye stud type markings.
Bangladesh
use of normal domestic paints for pavement markings
no uniformity/consistency of road markings
absence of required markings at potentially hazardous locations
most of the road users are not aware of the meaning of road markings
Introduction
it is a physical device which is use to control traffic movement at the junction
it replaces the priority regulation of junction operation
it assigns the right-of-way by splitting green time to the various traffic movements
Warrants
when traffic flow at uncontrolled/priority-controlled junction become high and thereby increases:
traffic conflicts and overall delay;
accidents probability;
when manual operation of junction with the help of traffic police become very difficult and expansive
Advantages
provide for orderly movement of traffic
increase traffic handling capacity of the intersection
reduce the frequency of certain types of accidents especially right angle and pedestrian
provide for nearly continuous movement of traffic at desired speed along a given route by co-ordination
Disadvantages
at off-peak periods signal controllers with fixed time & plan cause unnecessary delay and increase drivers irritation
- in consequence promote disrespect of the signal indication
increase in certain types of accidents (especially rear-end collisions- at dilemma zones)
Terminology
Signal sequence Green -> Amber -> Red -> Red/Amber
Phase - That part of a cycle allocated to a stream or combination of two or more streams having the right of way
simultaneously.
Filter signals - it is mounted alongside the main signals to permit movement of vehicles in the direction shown by
the green arrow even though the main signal is showing red.
Amber period/Clearance time (a) - to allow vehicles to clear the junction. Usually 3 secs; high speeds junction
3-6 secs.
Inter-green period (I) - the time from the end of the green period to the phase losing right-of-way to the beginning
of the green period of the phase gaining right-of-way.
Optimum cycle length (Co) - the cycle time which gives the least average delay to all vehicles using the
intersection
Lost time (l) - the time which is effectively lost to traffic movement in a phase because of starting delays and the
falling-off discharge rate during the amber period.
Effective green time (g) - the time during the cycle when traffic flows freely discharge through the green aspect at
the maximum rate; it is the sum of the green period and the amber period less the lost time for the particular phase
All-red period - a red period between the amber and red/amber shown to all approaches in order to allow vehicles
to clear the junction safely before starting of the next phase: it is usually needed:
when junction is large
when there are slow moving vehicles in the traffic stream
when there are right turning vehicles left over at the end of the phase
when pedestrian movements are high in all directions and demand "pedestrian only" phase
Saturation flow (S) - the maximum rate of discharge for a particular approach.
Important Relationships
Cycle time, C = (s, q, L); where, s = saturation flow/capacity; q = arrival flow/demand; L = lost times
Intergreen, I = a + all-red
Cycle time, C = G + I
green period, G = g + LI + LF; where, g = Effective green; LI, LF = initial and final lost time
Total lost time/cycle,L = all-red + lost time
= (I-a) + (LI + LF)
Right-of-way = G + A = g + lost time
Maximum/dominant ratio of flow (q) to saturation flow (s) for a given phase of critical lane, y = q/s
Optimum cycle, Co = (1.5 L + 5)/(1-Y) in seconds; where, Y = y1 + y2 .yn; n = total no. of phase in cycle
For optimum conditions,
Green time split: g1/g2 = y1/y2 = (Co - L)/Y
Local Problems
No. standard for signal setting & design:
Set at far away from the intersections and encourage drivers to stop beyond the signal mast.
Signals are installed even where they are not warranted.
Signal light size(lens dia.) and lumination is inadequate.
Cycle times and phasing are judgment based; amber clearance phases are short and inadequate for safe
rickshaw clearance and above all a single timing plan is maintained throughout the day.
Traditionally, drivers watch the policeman rather than the signals.
Un-enforced signals discourages drivers compliance in general and thereby weakening the overall level of respect
for traffic signals.
Green Filter
G A R G A R
R R
A A
G G
Intergreen Intergreen
G A R G Phase 1
R G A R Phase 2
Cycle Time, C
Intergreen Intergreen
G A R Phase 1
R G A Phase 2
All-Red
Saturation flow
Time
G A R
Solution
North South East West
y = flow/sat.flow = 0.22 0.25 0.30 0.26
ydominating = 0.25 0.30
Y = yNS + yEW = 0.56
GNS = 19 s
Inter-green, NS = 6 s
GEW = 21 s
Inter-green, EW = 7 s
Cycle time, Co = 53 s
Solution
North South East West
y = flow/sat.flow = 0.25 0.28 0.32 0.27
ydominating = 0.28 0.32
Y = yNS + yEW = 0.60
GNS = 24 s
Inter-green, NS = 9 s
GEW = 27 s
Inter-green, EW = 6 s
Cycle time, Co = 66 s
Introduction
Perception requires greater time at low level of illumination
Good visibility is a prerequisite to good traffic operation
For night driving on roads, although all the motor vehicles have their own head lights which are quite sufficient, still
adequate lighting on roads is essential for other road users viz. non-motorized vehicles (cycles, rickshaws, carts
etc.), pedestrian who have not their own lights
A large proportion of the road accidents are caused in the night and one of the main reasons is the insufficient
lighting
In the absence of street light, drivers are forced to use dip-beam of head-lights which causes glaring problem
and often lead to severe accidents
Objectives/Possible Benefits
Adequate street lighting -
Enable road users to see clearly the roadway
Make drivers confident in their maneuvers
Encourages use of full roadway width
Reduces use of dip-beam
Reduces night time crime
Improves personal security
Promotes business
Installation Requirements
To get uniform lit road surface, the following issues should be considered carefully:
Mounting height
Spacing
Overhang
Luminous intensity/brightness
Surface type
a) Determination of spacing
Average pavement illumination = Total effective illumination/Total area to be illuminate
= (L x Cu)/(S x W)
Where;
L = Lumen output of light source (strength of source)
Cu = Co-efficient of utilization (i.e. effective lumen of light on the pavement, which depends on the ratio of
road width and mounting height)
S = Spacing of light post
W = Width of pavement
Problems
An urban secondary road, with 50ft pavement width having a reflectance of 10%, carries a maximum of 1000 vph at
night-time in both directions. Design lighting system of the road considering sodium light source with mounting height
of 40ft and a maintenance factor of 0.8. Draw the lighting layout.
Solution
i) Actual Average Illumination (AAI):
From Table 1; average recommended illumination = 0.8 L/ft2
From Table 2; adjustment factor for surface reflectance = 1
Therefore, AAI = 0.8 x 1 = 0.8
0.55
0.5
0.45
0.4
Co-efficient of Utilization
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5
Ratio = Road width/Mounting Height
Note: Due to poor maintenance, the actual co-efficient of utilization is reduced by a factor usually 0.8 (i.e. taken as 80%).
Background
While in motion larger sized vehicles viz. buses/trucks cause significant effects on traffic operation as they
are slow
occupy large road space
have poor maneuver capability
require large turning radius
take longer time for loading and unloading
Moreover, uncontrolled parking of these empty vehicles has many adverse effects on traffic operation. In this regard,
terminal facility is considered as a measure of traffic control and management.
Objectives
To provide regulated loading/unloading and parking/ repairing facilities for buses
To provide regulated parking/repairing facilities for empty trucks
BUS TERMINALS
Introduction
Terminals provide bus layover areas, where passengers loading/unloading are taken place
In a town, it is desirable to provide a properly designed bus terminal to handle exclusively long distance inter-city
bus traffic
The terminals should be planned for the anticipated future traffic in the design year
Location
Bus terminals should preferably be outside the congested portions of the town (out skirt of the city)
If a town has ring road, ideal location in many cases is on the ring road
Regulations
To ensure proper functioning and effective use, terminals should
be regulated and controlled properly
have queue discipline
maintain strict scheduling and ensure minimum layover at the queue
not be allowed to use for repair purposes
Terminal Requirements
Terminal should be planned in such a way that one-way circulation of buses is achieved
Due to heavy passengers activities, measure (barrier, sufficient waiting place, etc.) should be taken to ensure
passengers movements not conflicts with vehicular movements
The platforms, where passengers wait should be raised
Provision for facilities such as cafeteria, book-stalls, phone booth, toilets etc. should be provided
Terminals should have feeder/transit facilities scheduled bus, train etc. services (i.e. easily accessible)
Parking facilities for cars, taxis, par-transit etc. should be provided liberally
Should have separate/isolated space for long time stay, fuelling facilities, workshop etc.
Introduction
Loading and unloading of goods by trucks on the roadside makes demands upon the spaces, which are reserved
for pedestrian as well as for moving vehicles
The problem can be controlled by permitting loading and unloading
only between lean period or
permitting loading and unloading only at specific locations
Empty trucks need spaces for parking terminal is the best solution where repairing, waiting for assignment can
be done without interrupting traffic movements
Truck traffic needs control on
parking for empty vehicles and
loading/unloading areas and time of operation
Terminal should be located at the fringes of the cities/on important arterial routes/close to major generators of
commercial activities
Should have ancillary facilities such as loading/unloading platform, weight bridge, storage, fuelling facilities,
workshop etc. in addition to the parking area
For single unit trucks a bay size of 3.75m X 7.5m is adequate and about 600 750 trucks can be
accommodated in a parking area of one hector
Terminology
Terminal - a place for the use of passengers joining or leaving a bus, ship etc. and freight loading/unloading of
trucks.
Depot - a place where buses/trucks are kept and repair.
Workshop - where heavy repairs and jobs on vehicles are done .
Bangladesh
Local Experiences
Excessive layover/stopover make terminal inefficient
Being used for repair and garage purposes
Uncoordinated/unscheduled services (because of many bus owners)
Poor queuing discipline
Competition for attracting passengers (fighting for passenger)
Drop-off/pick-up passengers at the entrance/exit of terminals
Hooliganism/trade union activities make terminal unsafe place for the passengers