Traffic signs perform a number of functions:
(i) They give timely warning of hazardous situations when they are not self-evident.
(ii) They are of great help in regulating traffic and
(iii) They give information as to highways routes , directions and places of interest.
These traffic signs should be backed by law in order to make them useful and effective. These are divided into the following three types:
(a) Danger signs , also know as Warning Signs.
(b) Signs giving definite instructions also known as Regulatory signs. These are further divided into (i) Prohibitory Signs and (ii) Mandatory Signs and
(c) Information Signs.
(a) Danger Signs or Warning Signs or Cautionary Signs:
Danger signs are used when it is deemed necessary to warn traffic of existing or potentially hazardous conditions on or adjacent to a highway or street. The use of warning signs should be kept to a minimum , because their unnecessary use tends to bread disrespect for all signs. The warning signs recommended by the IRC are illustrated in Fig 6.1. The side of the triangle is 900mm for a standard size and 600 mm for a reduced size. These signs have a red border and the symbols indicated there in are in black colour against a white back ground.
(b) Regulatory signs: These signs are intended to inform the highway users of traffic laws or regulations. These are of two types:
(i) Prohibitory Signs: These signs given definite negative instructions prohibiting the motorist from making particular manoeuvres. eg: over taking prohibited , one-way traffic , waiting restrictions , restrictions on dimensions , speed of vehicle etc. These are of circular shape , with a dia. of 600mm for signs of the standard size and 400mm for reduced size. The signs have a red border. The colour of the background is white for speed control and blue for other signs. The symbols are black in colour on white background and white in colour on blue background. These signs are illustrated in Fig 6.2.
(ii) Mandatory Signs are part of regulatory signs and are intended to convey definite positive instructions when it is desired that motorists take some positive action. The two important mandatory signs are the STOP sign and YIELD or GIVE WAY sign Fig. 6.3. The stop sign requires all the vehicles to come to a halt before the stop line. Stop sign is an octagon with a white border and a red background , the side of the octagon being either 900 mm or 600 mm.
It shall be used in combination with a definition plate carrying the message ‘STOP’.
Fig 6.1 WARNING SIGNS
Fig 6.2 REGULATORY SIGNS
THE YIELD or GIVE WAY sign (Fig 6.3) is a downward pointing equilateral triangle having a red border and a white background. The side of the equilateral triangle is either 900 mm or 600 mm. It shall be used in combination with a definition plate carrying the message “GIVEWAY”. This sign is used to assign right-of way to traffic on certain approaches to an intersection. Vehicles controlled by a YIELD sign need stop only when necessary to avoid interference with other traffic.
(c) Informatory Signs: These signs are intended to guide the road user and to give such information as may be of interest during travel. An informatory sign is made of a rectangular board of specified size. The common informatory signs used are ‘Road Junction approach’ , End of speed limit; and ‘Parking Sign’.
Fig 6.3 STOP AND GIVE WAY SIGNS
These informatory signs are shown in Fig 6.4. Route marker signs are provided before intersections , particularly to indicate the National Highway route (Fig 6.5).
Fig 6.4. INFORMATORY SIGNS
Locations of Traffic Signs: In India , the signs are located on the left side of the road. The signals are mounted at a height of 1.5m for unkerbed roads and 2m for kerbed roads.
Stop Signs: To be located at the point where the vehicle has to stop or as near thereto as possible - say 3 metres ; in the case of pedestrians crossings 1.2m ahead.
Give way sign: To be located as near to the point where the vehicle is to stop - say at a distance 3m.
Warning Sign: In the case of urban location 50m ahead of the hazard and non-urban locations depends on the type of terrain and importance of the road.
FIG 6.5. ROUTE MARKER SIGN 6.3.2. TRAFFIC SIGNALS:
These are provided at large intersections for safe and efficient movement of vehicular traffic and pedestrians. At small intersections , traffic is controlled by the traffic police , alternately showing ‘stop’ sign to the incoming roads.
Advantages of traffic signals are:
(i) Movements of traffic at the intersections is more orderly and safe.
(ii) Traffic handling capacity at intersections is increased.
(iii) They improve the quality of traffic flow as compared to the police control.
(iv) The signal indications can very easily be understood even in foggy weather or at night.
Disadvantages of traffic signals are:
(i) They generally increase the total vehicle delay at intersections during off-peak hours.
(ii) They cause an increase in rear-end collisions.
(iii) Electric power failure of the signal installations may lead to serious and wide spread traffic difficulties.
A typical signal head is shown in Fig 6.6. Traffic signals have three coloured light glows facing each direction of traffic flow. The red light is meant for STOP , the green light indicates GO and the amber of yellow light shows CLEARANCE TIME for the vehicles which enter the intersection area by the end of green time , to clear off. These are placed on
the left hand side of the road and are illuminated in such a way that they are visible from a distance 0.4 km under normal atmospheric conditions. Based on their operating principles and functions traffic signals are classified into the following groups.
Fig 6.6. TRAFFIC SIGNALS
(i) Traffic Control Signals: (a) Fixed - time signals , (b) Manually operated Signals and (c) Traffic Actuated (Automatic) Signals.
(ii) Pedestrian signals , and (iii) Special Traffic Signals.