Lecture notes in Traffic Engineering And Management
Date: February 19, 2014
Traffic control device is the medium used for communicating
between traffic engineer and road users.
Unlike other modes of transportation, there is no control on the drivers using
Here traffic control devices comes to the help of the traffic engineer.
The major types of traffic control devices used are- traffic signs, road
markings , traffic signals and parking control.
This chapter discusses traffic control signs.
Different types of traffic signs are regulatory signs, warning signs and
The requirements of traffic control devices are listed below:
A number of mechanisms are used by the traffic engineer to communicate with the
These mechanisms recognize certain human limitations, particularly eyesight.
Messages are conveyed through the following elements.
- The control device should fulfill a need : Each device must have a
specific purpose for the safe and efficient operation of traffic flow.
The superfluous devices should not be used.
- It should command attention from the road users: This affects the
design of signs.
For commanding attention, proper visibility should be there.
Also the sign should be distinctive and clear.
The sign should be placed in such a way that the driver requires no extra
effort to see the sign.
- It should convey a clear, simple meaning:
Clarity and simplicity of message is essential for the driver to properly
understand the meaning in short time.
The use of color, shape and legend as codes becomes important in this regard.
The legend should be kept short and simple so that even a less educated driver
could understand the message in less time.
- Road users must respect the signs:
Respect is commanded only when the drivers are conditioned to expect that all
devices carry meaningful and important messages.
Overuse, misuse and confusing messages of devices tends the drivers to ignore
- The control device should provide adequate time for proper response
from the road users:
This is again related to the design aspect of traffic control devices.
The sign boards should be placed at a distance such that the driver could see
it and gets sufficient time to respond to the situation.
For example, the STOP sign which is always placed at the stop line of the
intersection should be visible for at least one safe stopping sight distance
away from the stop line.
There are several hundreds of traffic signs available covering wide variety of
traffic situations. They can be classified into three main categories.
- Color: It is the first and most easily noticed characteristics of
Usage of different colors for different signs are important.
The most commonly used colors are red, green, yellow, black, blue, and brown .
These are used to code certain devices and to reinforce specific messages.
Consistent use of colors helps the drivers to identify the presence of sign
- Shape : It is the second element discerned by the driver next to
the color of the device.
The categories of shapes normally used are circular, triangular, rectangular,
and diamond shape.
Two exceptional shapes used in traffic signs are octagonal shape for STOP sign
and use of inverted triangle for GIVE WAY (YIELD) sign.
Diamond shape signs are not generally used in India.
- Legend : This is the last element of a device that the drive
This is an important aspect in the case of traffic signs.
For the easy understanding by the driver, the legend should be short, simple
and specific so that it does not divert the attention of the driver.
Symbols are normally used as legends so that even a person unable to read the
language will be able to understand that.
There is no need of it in the case of traffic signals and road markings.
- Pattern: It is normally used in the application of road markings,
complementing traffic signs.
Generally solid, double solid and dotted lines are used.
Each pattern conveys different type of meaning.
The frequent and consistent use of pattern to convey information is recommended
so that the drivers get accustomed to the different types of markings and can
instantly recognize them.
In addition special type of traffic sign namely work zone signs are also
These type of signs are used to give warning to the road users when some
construction work is going on the road.
They are placed only for short duration and will be removed soon after the work
is over and when the road is brought back to its normal condition.
The first three signs will be discussed in detail below.
These signs are also called mandatory signs because it is mandatory that the
drivers must obey these signs.
If the driver fails to obey them, the control agency has the right to take
legal action against the driver.
These signs are primarily meant for the safety of other road users.
These signs have generally black legend on a white background.
They are circular in shape with red borders.
The regulatory signs can be further classified into :
- Regulatory signs: These signs require the driver to obey the signs
for the safety of other road users.
- Warning signs:These signs are for the safety of oneself who is
driving and advice the drivers to obey these signs.
- Informative signs: These signs provide information to the driver
about the facilities available ahead, and the route and distance to reach the
Some examples of the regulatory signs are shown in figure 1. They
include a stop sign, give way sign, signs for no entry, sign indicating
prohibition for right turn, vehicle width limit sign, speed limit sign etc.
- Right of way series: These include two unique signs that assign
the right of way to the selected approaches of an intersection.
They are the STOP sign and GIVE WAY sign
For example, when one minor road and major road meets at an intersection,
preference should be given to the vehicles passing through the major road.
Hence the give way sign board will be placed on the minor road to inform the
driver on the minor road that he should give way for the vehicles on the major
In case two major roads are meeting, then the traffic engineer decides based on
the traffic on which approach the sign board has to be placed.
Stop sign is another example of regulatory signs that comes in right of way
series which requires the driver to stop the vehicle at the stop line.
- Speed series: Number of speed signs may be used to limit the speed
of the vehicle on the road.
They include typical speed limit signs, truck speed, minimum speed signs etc.
Speed limit signs are placed to limit the speed of the vehicle to a particular
speed for many reasons.
Separate truck speed limits are applied on high speed roadways where heavy
commercial vehicles must be limited to slower speeds than passenger cars for
Minimum speed limits are applied on high speed roads like expressways, freeways
etc. where safety is again a predominant reason.
Very slow vehicles may present hazard to themselves and other vehicles also.
- Movement series: They contain a number of signs that affect
specific vehicle maneuvers.
These include turn signs, alignment signs, exclusion signs, one way signs etc.
Turn signs include turn prohibitions and lane use control signs.
Lane use signs make use of arrows to specify the movements which all vehicles
in the lane must take.
Turn signs are used to safely accommodate turns in unsignalized intersections.
- Parking series: They include parking signs which indicate not only
parking prohibitions or restrictions, but also indicate places where parking is
permitted, the type of vehicle to be parked, duration for parking etc.
- Pedestrian series: They include both legend and symbol signs. These
signs are meant for the safety of pedestrians and include signs indicating
pedestrian only roads, pedestrian crossing sites etc.
- Miscellaneous: Wide variety of signs that are included in this
category are: a "KEEP OF MEDIAN" sign, signs indicating road closures, signs
restricting vehicles carrying hazardous cargo or substances, signs indicating
vehicle weight limitations etc.
Warning signs or cautionary signs give information to the driver about the
impending road condition.
They advice the driver to obey the rules.
These signs are meant for the own safety of drivers.
They call for extra vigilance from the part of drivers.
The color convention used for this type of signs is that the legend will be
black in color with a white background.
The shape used is upward triangular or diamond shape with red borders.
Some of the examples for this type of signs are given in fig 2 and
includes right hand curve sign board, signs for narrow road, sign indicating
railway track ahead etc.
Examples of regulatory signs ( stop sign, give way sign, signs for no
entry, sign indicating prohibition for right turn, vehicle width limit sign,
speed limit sign)
Informative signs also called guide signs, are provided to assist the drivers
to reach their desired destinations.
These are predominantly meant for the drivers who are unfamiliar to the place.
The guide signs are redundant for the users who are accustomed to the location.
Examples of cautionary signs ( right hand curve sign board, signs for
narrow road, sign indicating railway track ahead)
Some of the examples for these type of signs are route markers, destination
signs, mile posts, service information, recreational and cultural interest area
Route markers are used to identify numbered highways.
They have designs that are distinctive and unique.
They are written black letters on yellow background.
Destination signs are used to indicate the direction to the critical
destination points, and to mark important intersections.
Distance in kilometers are sometimes marked to the right side of the
They are, in general, rectangular with the long dimension in the horizontal
They are color coded as white letters with green background.
Mile posts are provided to inform the driver about the progress along a
route to reach his destination.
Service guide signs give information to the driver regarding various services
such as food, fuel, medical assistance etc.
They are written with white letters on blue background.
Information on historic, recreational and other cultural area is given on white
letters with brown background.
In the figure 3 we can see some examples for informative signs which
include route markers, destination signs, mile posts, service center
Traffic signs are means for exercising control on or passing
information to the road users.
They may be regulatory, warning, or informative.
Among the design aspects of the signs, the size, shape, color and location
Some of the signs along with examples were discussed in this chapter.
A few web sites discussing on traffic signs are given below:
Examples of informative signs (route markers, destination signs, mile
posts, service center information etc)
I wish to thank several of my students and staff of NPTEL for their contribution in this lecture.
- L. R Kadiyali.
Traffic Engineering and Transportation Planning.
Khanna Publishers, New Delhi, 1987.
Prof. Tom V. Mathew