Lecture 11 Transportation and Traffic Engineering (CE 351)
Traffic Signal
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 slitting green time to the various traffic movements
Warrants
When traffic flow at uncontrolled / priority-controlled junction become high and thereby
increases traffic conflicts, delay, accident probability
When manual operation of junction with the help of traffic police become very difficult
and expensive
Advantages
Provide for orderly movement of traffic
Increase traffic handling capacity of the intersection
Reduce the frequency of certain types of accidents
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 read-end collisions)
Signal Installation Consideration
Signal should be only be used where by they are required and where they will be respected
Traffic signal should be kept functioning with quick repair times so that drivers continue
to rely on traffic signals
Types of Signal Controller
Fixed-time Controller
- Green time, total cycle period is pre determined and to fixed duration
- The controllers are simple and relatively cheaper but they are necessarily
inflexible and require careful setting
Vehicle-actuated Demand responsive Controllers (online/real time system)
- Green time are related to traffic demands and provision is there to omit
particular phase is there is no traffic
1 Md.Yusuf Ali
Lecture 11 Transportation and Traffic Engineering (CE 351)
- Need to install detectors on all approaches
- Delay is minimized globally
Modern Computer based area coordinated controllers
- With the system green time calculation is made instantly based on prefixed
delay minimizing algorithm
Local Problems in Bangladesh
No standard for signal setting and design
Signals are installed even where they are not warranted
Signal light size and illumination is inadequate
Cycle times are judgment based and same cycle time is maintained throughout the day
Traditionally, drivers watch policeman rather than the signals
Un-enforced signals discourage to obey the signal and thereby weakening the overall
level of respect for traffic signals.
TERMINALS
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, ills desirable to provide a properly designed bus terminal to handle exclusively
long distance inter-city bus traffic.
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Lecture 11 Transportation and Traffic Engineering (CE 351)
The terminals should be planned for the anticipated future traffic in the design year
Locations
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.
TRUCK TERMINALS
(For Commercial/Freight Traffic)
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
o only between lean period or
o Permitting loading and unloading only at specific locations.
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Lecture 11 Transportation and Traffic Engineering (CE 351)
Empty trucks need spaces for parking — terminal is the best solution, where repairing,
waiting for assignment be done without interrupting traffic movements.
Truck traffic needs control on
o parking for empty vehicles and
o 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
car 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 trucks.
Depot - a place where buses/trucks are kept and repair.
Workshop- where heavy repairs and jobs on vehicles are done
In Context of Bangladesh
Local Experiences
o Excessive layover/stopover make terminal inefficient.
o Being used for repair and garage purposes.
o Uncoordinated/unscheduled services (because of many bus owners).
o Poor queuing discipline.
o Competition for attracting passengers (fighting for passenger).
o Drop-off/pick-up passengers at the entrance/exit of terminals.
o Hooliganism/trade union activities make terminal unsafe place for the passengers.
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