Traffic Signs
Lecture Notes in Transportation Systems Engineering
Contents
______________________________________________________________________
1 Overview
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 the road. 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 informatory
signs.
2 Requirements
The requirements of traffic control devices are listed below:
- 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 them.
- 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.
3 Communication tools
A number of mechanisms are used by the traffic engineer to communicate with the road user.
These mechanisms recognize certain human limitations, particularly eyesight. Messages are
conveyed through the following elements.
- Color: It is the first and most easily noticed characteristics of a device. 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 board ahead.
- 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 comprehends. 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.
4 Types of traffic signs
There are several hundreds of traffic signs available covering wide variety of traffic situations.
They can be classified into three main categories.
- 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 specific
destinations
In addition special type of traffic sign namely work zone signs are also available. 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.
4.1 Regulatory signs
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
:
- 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 road. 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 safety reasons. 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.
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.
4.2 Warning signs
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.
4.3 Informative signs
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.
Some of the examples for these type of signs are route markers, destination signs,
mile posts, service information, recreational and cultural interest area signing etc.
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 destination. They are, in general, rectangular with the long
dimension in the horizontal direction. 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 information etc..
5 Summary
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 matters. Some of the signs along with examples were
discussed in this chapter. A few web sites discussing on traffic signs are given below:
www.aptransport.org/html/signs.htm, www.indiacar.com/infobank/Traffic-signs.htm.
Exercises
- What is the difference between a stop sign and give way sign? Under what
circumstances are they required? Illustrate with neat sketches.
- Give two examples for each of the following categories of traffic signs: (i) Right of
way series, (ii) Movement series, (iii) Informatory signs, and (iv) Warning signs
- Give one example (with neat sketch) each for traffic signs (i) for your own safety,
(ii) for the safety of other road users, and (iii) not specifically for safety purposes.
References
- L R Kadiyali. Traffic Engineering and Transportation Planning. Khanna
Publishers, New Delhi, 1987.
Acknowledgments
I wish to thank several of my students and staff of NPTEL for their contribution in
this lecture. I also appreciate your constructive feedback which may be sent to
tvm@civil.iitb.ac.in
Prof. Tom V. Mathew
Department of Civil Engineering
Indian Institute of Technology Bombay, India
_________________________________________________________________________
Wednesday 27 September 2023 11:05:26 PM IST