Design of traffic signals - concepts

Basic concepts and formulae regarding design of traffic signals

The conflicts arising from movements of traffic in different directions is addressed by time sharing principle. The design principles of traffic signal are:

• phase design
• cycle length design and 
• green splitting. 

In this regard, the concepts of saturation flow, capacity, and lost times are important.

Cycle: A signal cycle is one complete rotation through all of the indications provided.

Cycle length:  Cycle length is the time in seconds that it takes a signal to complete one full cycle of indications. It is denoted by C.

Interval: Thus it indicates the change from one stage to another. There are two types of intervals - change interval and clearance interval. Change interval is also called the yellow time indicates the interval between the green and red signal indications for an approach. Clearance interval is also called all red and is provided after each yellow interval indicating a period during which all signal faces show red and is used for clearing off the vehicles in the intersection.

Green interval: It is the green indication for a particular movement or set of movements and is denoted by Gi. This is the actual duration the green light of a traffic signal is turned on.

Red interval: It is the red indication for a particular movement or set of movements and is denoted by Ri. This is the actual duration the red light of a traffic signal is turned on.

Phase:  A phase is the green interval plus the change and clearance intervals that follow it. Thus, during green interval, non conflicting movements are assigned into each phase. It allows a set of movements to flow and safely halt the flow before the phase of another set of movements start.

Lost time: It indicates the time during which the intersection is not effectively utilized for any movement. For example, when the signal for an approach turns from red to green, the driver of the vehicle which is in the front of the queue, will take some time to perceive the signal (usually called as reaction time) and some time will be lost before vehicle actually moves and gains speed.

The signal design procedure involves six major steps. They are: 

• phase design
• determination of amber time and clearance time
• determination of cycle length
• apportioning of green time
• pedestrian crossing requirements and 
• performance evaluation of the design

There is no precise methodology for the design of phases. It is often guided by:

• the geometry of the intersection
• the flow pattern especially the turning movements and
• the relative magnitudes of flow. 

A trial and error procedure is often adopted. The first issue is to decide how many phases are required. It is possible to have two, three, four or even more number of phases. 

Cycle time is the time taken by a signal to complete one full cycle of iterations. i.e. one complete rotation through all signal indications. It is denoted by C.

As the signal is initiated, the time interval between two vehicles, referred as headway, crossing the curb line is noted. The first headway is the time interval between the initiation of the green signal and the instant vehicle crossing the curb line. The second headway is the time interval between the first and the second vehicle crossing the curb line.

The first headway will be relatively longer since it includes the reaction time of the driver and the time necessary to accelerate. The second headway will be comparatively lower because the second driver can overlap his/her reaction time with that of the first driver’s. After few vehicles, the headway will become constant. This constant headway which characterizes all headways beginning with the fourth or fifth vehicle, is defined as the saturation headway, and is denoted as h.

The saturation flow rate s= 3600/h

Start-up lost time (L)

Green time (T) to clear N vehicles

Effective green time is the actual time available for the vehicles to cross the intersection. It is the sum of actual green time (Gi) plus the yellow minus the applicable lost times.

The ratio of effective green time to the cycle length (gi/C) is defined as green ratio. We know that saturation flow rate is the number of vehicles that can be moved in one lane in one hour assuming the signal to be green always. Then the capacity of a lane can be computed as,

Saturation flow rate can be computed as, 

Lane capacity is 

y is the length of yellow interval in seconds

t is the reaction time of driver

V85 is the 85th percentile of speed of approaching vehicles in m/s

a is the deceleration rate of approaching vehicles in m/s2

g is the grade of approach as a decimal

The flowchart depicting the various stages in the design of a traffic signal is shown below

Road Safety Engineering - Problems

 ROAD SAFETY ENGINEERING PROBLEMS

• Accident Rate per Kilometer

        Number of accidents of all types per km of each highway and street classification.

        R = A/L

        R = total accident rate per km for one year,
        A = total number of accident occurring in one year,
        L = length of control section in km

• Death rate based on population
  
  Number of traffic fatalities per 100,000 populations.
  
  R = (B × 100000 )/ P
  
  R - death rate per 100,000 population,
  B = total number of traffic death in one year and
  P = population of area

• Death rate based on registration

        Number of traffic fatalities per 10,000 vehicles registered.

        R = (B × 10000) / M

        R - death rate per 10,000 vehicles registered,
        B - total number of traffic death in one year
        M - number of motor vehicles registered in the area 

• Accident involvement Rate

        Numbers of drivers of vehicles with certain
        Characteristics who were involved in accidents per 100 million vehicle-kms of travel.

        R = (N × 100000000)/V

        R - accident involvement per 100 million vehicle-kms of travel,
        N - total number of drivers of vehicles involved in accidents during the period of investigation
        V - vehicle-kms of travel on road section during the period of investigation

• Accident Rate based on vehicle-kms of travel

        Number of accidents per 100 million vehicle km of travel.

        R = (C × 100000000)/V

        R = accident rate per 100 million vehicle kms of travel,
        C = number of total accidents in one year and
        V = vehicle kms of travel in one year

PROBLEM

The Motor vehicle consumption in a city is 5.082 million liters, there were 3114 motor vehicle fatalities, 355,799 motor vehicle injuries, 6,721,049 motor vehicle registrations and an estimated population of 18,190,238. Kilometer of travel per liter of fuel is 12.42 km/liter. Calculate registration death rate, population death rate and accident rate per vehicle km.

Solution: 

 Approximate vehicle km of travel = Total consumption of fuel × kilometer of travel per liter of fuel                                                             =5.08 × 106 × 12.42 = 63.1 × 106 km.

Registration death rate can be obtained from

R = (B × 10, 000) /M

R is the death rate per 10,000 vehicles registered, 

B (Motor vehicle fatalities) is 3114, M 

(Motor vehicle registered) is 6.72 × 106.

Hence

R =(3114 × 10000) /6.72 × 106 = 4.63

Population Death Rate can be obtained from the equation.

R =(B × 100, 000)/P

Here, R is the death rate per 100,000 population

B (Motor vehicle fatalities) is 3114, 

P(Estimated population) is = 18.2 × 106.

R =(3114 × 100000)/18.2 × 106 = 17.1

Accident rate per vehicle kms of travel can be obtained from the equation below as:

R =(C × 100, 000, 000) / V

Here, 

R is the accident rate per 100 million vehicle kms of travel, 

C (total accident same as vehicle fatalities) is 3114

V (vehicle kms of travel) is 63.1 × 109.

R =(3114 × 100 × 106 )/63.1 × 109 = 4.93

Safety Barriers

SAFETY BARRIERS

• Safety barriers are designed to withstand the impact of vehicles of certain weights at certain angle while traveling at the specified speed. 
• They are expected to guide the vehicle back on the road while keeping the level of damage to vehicle as well as to the barriers within acceptable limits.
• Ideally a crash barrier should present a continuous smooth face to an impacting vehicle, so that the  vehicle is redirected, without overturning, to a course that is nearly parallel to the barrier face and with a lateral deceleration, which is tolerable to the motorist. 
• To achieve these aims the vehicle must be redirected without rotation about both its horizontal or vertical axis (that is, without ‘spinning out’ or overturning), and the rate of lateral deceleration must be such as to cause the minimum risk of injury to he passengers.

Objectives of safety barriers

• Reducing the likelihood of a vehicle crossing the central reserve and reaching the opposite carriageway.
• Minimising the damage to a barrier and vehicle, following vehicle strike and also reducing the risk to the workforce and work related congestion.
• Being maintenance-free and having a life of 25 to 50 years. 

According to the IRC (6-2000) the crash barriers shall be provided at the following locations: 

• For bridges without foot paths, concrete crash barriers shall be provided at the edge of the carriageway. 
• The type design for the crash barriers may be adopted as per IRC:5
• The design loading for the barriers shall be as per IRC:6. 
• For bridges with foot paths, pedestrian railing shall be provided on the outer side of footpath
• The railings of existing bridges shall be replaced by crash barriers
• In the urban environment traffic barriers are needed on urban motorways and primary distributors, where speeds are high and dangerous. 
• Traffic barriers should be erected on both sides of roads on embankments 6m high or more and on the outer edge of the roads where the radius is 850m or less and the embankment height 3m or more. 
• It is important to provide suitable and treatment for such type of barrier in view of safety. The ends of this barrier must either be embedded into ground by tapering down or these must be embedded into the rigid parapet wall of a culvert or specially prepared rigid parapet fit the purpose of embedding

Road side rest areas

 ROAD SIDE REST AREAS

In order to promote road safety and avoid accidents due to long and incessant driving on national highways, the Ministry of Road Transport & Highways (MoRTH) has decided to develop wayside amenities including rest area for drivers and road users. The rest area facilities are proposed to be made available under Public Private Partnership (PPP) mode for which interest has been invited by the National Highways Authority of India (NHAI).

The general guidelines for establishing rest areas are listed below:

• The governing consideration for establishing road side rest areas is that it should ensure free flow of traffic on the road and ensure minimum interference by vehicles using the facility while ensuring safety of vehicles on the road
• Rest areas should have various amenities for users, e.g. places for parking, toilets, restaurants, rest rooms, kiosks for selling sundry items, bathing facilities, repair facilities, creche etc
• Location of the rest area should not interfere with future improvements of the highway
• Rest areas should be located where highway alignment and profile are favourable
• The proposed location should not interfere with placement and proper functioning of highway signs, signals, lighting or other devices that affect traffic operation 

Traffic aid posts

TRAFFIC AID POSTS

Since full-fledged traffic stations require huge investments and personnel, they cannot be established in several locations. This gave rise to small single-sized rooms that are located in various parts of the town at a distance from the main traffic station. The function of these posts is to maintain a smooth flow of traffic, issue traffic fine challans to offenders and attend to any accidents by reporting to the main traffic station,  clearing the road of debris and ensuring smooth flow of traffic.

• Traffic aid posts should be established at regular intervals on all important highways. 
• Highway patrols should be instituted on main highways and cranes should be available to remove vehicles involved in accidents or stalled.

Design of traffic signals - Problems

PROBLEMS ON THE DESIGN OF TRAFFIC SIGNALS

1.    Given:

• Cycle time at an intersection = 60 s     
• Green time for a phase  =  27 s
• Yellow time  =  4 s 
• Saturation headway = 2.4 s/vehicle
• Start-up time lost  =  2 s/phase
• Clearance lost time  =  1 s/phase

Calculate the capacity of movement per lane

2.    In a right angled intersection of two roads, one road has four lanes with a total width of 12 m. The other road has two lanes with a total width of 6.6 m. The traffic volume of two approaching roads is 900 and 743 PCU per hour. Design the signal timing as per IRC guidelines

3.    The average speed on a roadway is 80 kmph. Under stopped conditions, the average spacing between vehicles is 6.9m. Determine the maximum flow of vehicles (road capacity)

4.    Fifteen minute traffic count on cross roads A and B during peak hour are observed as 178 and 142 vehicles per lane respectively approaching the intersection in the observed direction of heavier traffic flow. If the amber times required are 3 and 2 seconds respectively for two loads based on approach speeds, design the signal timings by trial cycle method assuming an average headway time of 2.5 seconds during green phase.

5.    The average normal flow of traffic on cross-roads A and B during design period are 400 and 250 PCU per hour. The saturation flow values on these roads are 1250 and 1000 PCU respectively. The all-red time required for pedestrian crossing is 12 seconds. Design the traffic signal by webster's method

Traffic Impact Attenuators

TRAFFIC IMPACT ATTENUATORS

• Traffic Impact Attenuators or Crash Impact Attenuators are impact absorbing devices installed in highly hazardous locations so as to reduce kinetic energy of the irregularly moving vehicle and to stop or redirect the vehicle away from the main hazard with least damage to life and property

 

• A safety crash barrier is a system engineered to prevent fatal injuries by absorbing shock energy and converting it into rotational energy. It functions by virtue of absorbing energy from the impact and deflecting it into the barrier. This energy is converted into rotational energy into the barrier.

 

• The attenuator acts as a protection cushion in the event of an accident. Impact attenuators are designed to absorb the colliding vehicles kinetic energy and bring it to stop safely

• By safely dissipating the vehicle's kinetic energy, impact attenuators help prevent fatal injuries.

 

•  Impact attenuators can be categorized by the method used to dissipate kinetic energy:
• Momentum transfer. Many early models used successive rows of sand- or water-filled barrels or modules. Momentum is transferred to the sand or water, reducing the speed of the impacting vehicle.
• Material deformation. Many newer attenuators use crushable materials (like various kinds of foam) that create a crumple zone, absorbing energy. Others flatten a corrugated steel guard rail section, or split a steel box beam.
• Friction. Some attenuators work by forcing a steel cable or strap through an angled slot or tube, converting kinetic energy into heat.
  

Delineators

TRAFFIC DELINEATORS

• Traffic delineators are devices which are used for guiding traffic through potentially hazardous road conditions or when there are confusing construction situations in effect at a given location. 
• Delineators provide highly visible boundaries which help to identify changes in traffic flow that alert drivers to upcoming road conditions like curves, on and off ramps, and other road changes up ahead.
• Traffic delineators include everything from cones to barrels, however the term delineator is used on those traffic control devices which are tall (height) and have a comparatively short diameter.
• One of the most important requirements of a delineator is that it should be visible over a long distance under normal conditions.
• Delineators should be able to withstand impact and hence they are made of rugged plastic
• They are often coated with retro-reflective sheet for increased visibility at night.
• There are different types of delineators. But the most common ones are:
• Open-top delineators
• Flat-panel delineators and
• Delineators with handles
• All the above listed delineators may or may not have reflective sheeting on them.
• Traffic delineators are generally used for channeling motor vehicle traffic through specific locations where it is necessary to guide motorists along a pathway that is different from the normal flow of traffic
• Traffic delineators are more effective as they are highly visible and extremely effective at establishing traffic flow around hazardous locations. They can also be effectively used for temporarily establishing a traffic pattern
• They are frequently used at construction sites or accident sites. Around work zones delineators are used to direct traffic safely around the work area in order to protect the drivers and construction workers.

Area traffic controls

 AREA TRAFFIC CONTROLS

An Area Traffic Control (ATC) System involves coordination of traffic signals over a complete network of signals covering an area that might be considered homogeneous from the point of view of traffic operation. Such a system is computer aided as the problem is extremely complex because of crossing of several routes at common intersections.

• ATC systems are intelligent, real-time, dynamic traffic control systems which are designed to effectively respond to rapid variations in dynamic traffic conditions. 

• It is an advanced process to control the traffic. It is a traffic responsive system that use data from vehicle detectors and optimize traffic signal time in real time. 

• The timing plan of traffic controllers changes automatically. The technique employs digital computers for achieving the desired objective.

Fixed traffic signals and vehicle actuated signals

Fixed and vehicle actuated signals 

• Fixed time signals are normally installed at the intersection of two major roads. 
• The signals will change even if no cars or pedestrians are present. 
• Fixed time signals are less efficient when traffic varies quite a bit through the day, but they are cost-effective because detectors are not required.
• Fixed-time signals are the rule in urban areas for reasons of regularity, network organization, predictability, and reducing unnecessary delay.

• Vehicle-Actuated Signals require actuation by a vehicle on one or more approaches in order for certain phases or traffic movements to be serviced. 
• They are equipped with detectors and the necessary control logic to respond to the demands placed on them. 
• Vehicle-actuated control uses information on current demands and operations, obtained from detectors within the intersection, to alter one or more aspects of the signal timing on a cycle-by-cycle basis.
• Timing of the signals is controlled by traffic demand.
• Variability allows the signal to allocate green time based on current demands and operations. 
• A proper clearance interval between the green & the red phases is also ensured.

The various advantages of actuated signals are stated below:

• They can reduce delay (if properly timed).
• They are adaptable to short-term fluctuations in traffic flow.
• Usually increase capacity (by continually reapportioning green time).
• Provide continuous operation under low volume conditions.
• Especially effective at multiple phase intersections.

    The main disadvantages are as following :

• If traffic demand pattern is very regular, the extra benefit of adding local actuation is minimal, perhaps non-existent.
• Installation cost is two to three times the cost of a pre-timed signal installation.
• Actuated controllers are much more complicated than pre-timed controllers, increasing maintenance costs.
• They require careful inspection & maintenance to ensure proper operation.

There are three basic types of actuated control, each using signal controllers that are somewhat different in their design:

1. Semi-Actuated Control
2. Full-Actuated Control
3. Volume-Density Control

The various types of detectors used for detection of vehicles are as following:

• Inductive loop detectors
• Magnetometer detectors
• Magnetic detectors
• Pressure-sensitive detectors
• Radar detectors
• Sonic detectors
• Microloop detectors etc.

In certain, less-trafficked areas, actuated signals (push buttons, loop detectors) may be appropriate; however, these must be programmed to minimize delay, which will increase compliance.

Fixed-time signals incur lower initial and ongoing maintenance costs than actuated signals.

Actuated signals in general are not preferable because of the maintenance requirements and upkeep of the detection on the street.

Drivers at unsignalized intersections benefit from a series of fixed-time signals, as they produce routine gaps in traffic that may be used to turn onto or cross the street. Fixed-time signals help make pedestrians an equal part of the traffic signal system by providing them with regular and consistent intervals at which to cross

Fixed-time signals incur lower initial and ongoing maintenance costs than actuated signals.

Actuated signals prioritize movement along the primary corridor and can present obstacles to cross traffic and pedestrians if timed to prioritize vehicle movements only.

Actuated signals should be timed to be as responsive to activation as possible, with delay kept to a minimum.

Many existing traffic signal controllers have the capacity to reduce delay, but remain in coordination rather than a free setting. Coordination, paired with long signal cycles, can result in delays of 80 seconds or more, reducing pedestrian compliance, increasing risk-taking behavior, and creating the impression that a push button is either non-responsive or malfunctioning.

At crossings where the signal is uncoordinated with adjacent traffic signals (free setting), designers can further reduce pedestrian delay by reducing the minimum green time. At coordinated signal locations, designers have multiple options to decrease delay, including increasing the permissive window, adjusting signal timing for responsiveness at certain times of day, and setting the signal to recall on the pedestrian phase.

In coordination with traffic signal timing, designers must consider spacing between traffic signals, looking at desirable crossing intervals to achieve a pedestrian-friendly environment.

 Fixed-time signals are recommended in all downtown areas, commercial centers, and urban areas in which pedestrians are anticipated or desired and speeds are intended to be low.

Use of semi- or fully-actuated signal operations should mainly be restricted to suburban arterials and rural roads. 

In areas with lower pedestrian traffic, actuation may be used along priority rapid transit corridors to increase the schedule reliability of transit service and avoid unnecessary delays.

 The responsiveness of an actuated signal should be prompt (as low as 5 seconds) based on the necessary transition time for approaching motorists to come safely to a stop. 

Wherever pedestrian movement crosses a high capacity transit line, major bicycle facility, or critical freight route, longer delays are acceptable.

For major bicycle routes, use upstream passive detection as opposed to push-button activation to minimize the time lag between detection and crossing.

Fully-actuated signal control may be used where vehicle and pedestrian volumes vary considerably throughout the day. 

Full-actuation can reduce the amount of delay by being responsive to ongoing shifts and patterns in the traffic system.

Semi-actuated control prioritizes the through movement of a major road and is not recommended on streets with frequent cross traffic or pedestrian demand from the minor approach unless a low cycle length is used (below 80 seconds). 

Any traffic signal with long delays for pedestrians may discourage crossings and become a barrier to travel, especially at busy intersections.

Actuated signals may be combined with a number of signalization treatments, including full signalization (of the major and minor approach) and pedestrian or half-signalization (stop sign on the minor approach).

Signalization is not always the best option for a given intersection. Stop or yield control may be preferable at intersecting local or residential streets.

Fixed-time signals are recommended in all downtown areas, central business areas, and urban areas in which pedestrians are anticipated or desired and speeds are intended to be low.

Use of semi- or fully-actuated signal operations should mainly be restricted to suburban arterials and rural roads. 

In suburban corridors, motorist compliance can be increased and delay reduced through use of actuation.

In areas with lower pedestrian traffic, actuation may be used along priority rapid transit corridors to increase the schedule reliability of transit service and avoid unnecessary delays.

The responsiveness of an actuated signal should be prompt (as low as 5 seconds) based on the necessary transition time for approaching motorists to come safely to a stop. 

In cases where the pedestrian movement crosses a high capacity transit line, major bicycle facility, or critical freight route, longer delays are acceptable.

For major bicycle routes, use upstream passive detection is preferred to push-button activation to minimize the time lag between detection and crossing.

Traffic signals affecting pedestrian safety

 TRAFFIC SIGNALS AFFECTING PEDESTRIAN SAFETY

It has been observed that most pedestrian accidents in built-up areas occur at intersections. The "Traffic Conflicts Technique" is used to examine risk to pedestrians at intersections. 

• It has been observed that reduction in speed reduces the pedestrian's risk
• A "zebra crossing" located less than 2m from the intersection increases the pedestrian safety
• The collected data must distinguish between accidents occurring during pedestrians walking against red light and green light
• An exclusive pedestrian signal phase was found to be extremely safety-beneficial. However, such traffic signals meant exclusively for pedestrians are possible only in small towns with a very low population
• Pedestrians crossing a road running with heavy traffic is influenced heavily by size of the town and traffic volume
• Short waiting times and police enforcement are the most efficient measures to reduce frequency of red-walking

Factors affecting design of traffic signals

FACTORS AFFECTING DESIGN OF TRAFFIC SIGNALS

The IRC method for designing traffic signs implies the following factors affect the design of traffic signals

• Cycle: A signal cycle is one complete rotation through all of the indications provided
• Cycle length: Cycle length is the time in seconds that it takes a signal to complete one full cycle of indications. It indicates the time interval between the starting of of green for one approach till the next time the green starts. It is denoted by C. 
• Interval: Thus it indicates the change from one stage to another. There are two types of intervals - 
• change interval and 
• clearance interval. 
• Change interval is also called the yellow time indicates the interval between the green and red signal indications for an approach. 
• Clearance interval is also called all red is included after each yellow interval indicating a period during which all signal faces show red and is used for clearing off the vehicles in the intersection.
• Green interval: It is the green indication for a particular movement or set of movements and is denoted by Gi. This is the actual duration the green light of a traffic signal is lit.
• Red interval: It is the red indication for a particular movement or set of movements and is denoted by Ri. This is the actual duration the red light of a traffic signal is lit.
• Phase: A phase is the green interval plus the change and clearance intervals that follow it. Thus, during green interval, non conflicting movements are assigned into each phase. It allows a set of movements to flow and safely halt the flow before the phase of another set of movements start.
• Lost time: It indicates the time during which the intersection is not effectively utilized for any movement. For example, when the signal for an approach turns from red to green, the driver of the vehicle which is in the front of the queue, will take some time to perceive the signal (usually called as reaction time) and some time will be lost here before he moves.

Illumination and location of traffic signals

ILLUMINATION AND LOCATION OF TRAFFIC SIGNALS

A traffic signal is used as an instructing device that indicates the road user to act according to the displayed sign. Following the traffic signal ensures road safety and to make things simple to understand, these signals have been using a universal colour code.

• Red is generally the sign of danger or warning and on traffic lights, it signals potential hazard ahead and hence, is an indicator for the motorists to stop. 
• A flashing red light indicates the same as the stop light, which is, basically, top stop. Once you have stopped, you can proceed ahead after making sure there’s no obstacle in your path.
• A yellow traffic light is a warning signal that lets you know that the red signal is about to be displayed. Hence, when you see the yellow light, you should start slowing down to come to a stop in anticipation of red light. 
• A flashing yellow light is basically a warning signal to make the road users alert and slow down if needed.
• The green light signals safety and the word GO.
•  A traffic signal setup includes controller, traffic lights and detection. The controller works as the ‘brain’ of the entire setup and has the information that is required to make sure the lights work as per the required sequences. Traffic signals can run under a variety of different modes which can be dependent on location and time of day.
• Traffic Signal power supplies supply power to traffic signal cabinets
• The traffic signal power supply is an electrical device in the control cabinet that converts AC to correct DC voltages for various devices in the traffic signal cabinet. The nominal voltage of the power supply is 24VDC
• One of the effective options used by traffic management teams is the use of LED or light-emitting diode lamps to be able to consume less power during operations. This will also make it easier to provide backup power, such as the use of uninterruptible power supply (UPS).
• The first illuminated traffic signal was installed in London, England, in 1868.
  
• The first electric traffic signal was installed in Cleveland, Ohio, in 1914.
  
• The first signal to use the familiar green, yellow, and red lights was installed in New York City in 1918. It was operated manually from an elevated observation post in the middle of the street
  
• A modern traffic signal system consists of three basic subsystems: the signal lights in their housing, the supporting arms or poles, and the electric controller. The signal lights and housing are known as the signal light stack. 
• A single stack usually consists of three lights: a green light on the bottom to indicate the traffic may proceed, a yellow light in the middle to warn traffic to slow and prepare to stop, and a red light on the top to indicate the traffic must stop.
  
• Each light has a fresnel lens which may be surrounded or hooded by a visor to make it easier to see the light in bright sunlight. 
• A fresnel lens consists of a series of concentric angled ridges on the outer surface of the lens which bend the light to focus it in a parallel beam. 
• The light stack may have a dark-colored backing plate to make the signals more distinguishable by blocking out surrounding lights from buildings and signs.
  
• The electric controller is usually mounted in a weather-proof box on one of the corners of the intersection. 
• More elaborate traffic signals may also have electromagnetic sensors buried in the roadway to detect the flow of traffic at various points.
  
• The lens for each light is made of tinted glass or plastic.
• The bulb, known as the lamp, is designed for long life. 
• The bulb is partially. surrounded by a polished metal reflector to direct the light forward. 
• The hood or visor is made from aluminum or molded plastic.
• The supporting arms or poles are usually made of galvanized steel for strength and corrosion-resistance. They may also be made of fiberglass. 
• The controller is housed in a steel or aluminum enclosure. 
• The electrical components within the controller consist of switches, relays, and timers
• The wiring between the components is copper with a heavy neoprene rubber or plastic insulation.
• Each signal lens shall be illuminated independently and should be clearly visible from a distance of at least 400 m under normal atmospheric conditions.

Location of signals

• The Indian Road Congress (IRC) defines a road traffic signal as any power operated by which traffic is regulated, warned or directed to take some specific action.
• The primary consideration in placement of signals is visibility
• Drivers approaching a signalised intersection should be given a clear indication of their right-of-way assignment
• The lateral and vertical angles of sight towards a signal face determined by typical driver eye position, vehicle design and the vertical longitudinal and lateral position of the signal face are the critical elements to be considered while determining the location of signals
• The geometry of each intersection to be signalised along with the vertical grades and horizontal curves  should be considered in signal face placement.

Traffic Signal face

TRAFFIC SIGNAL FACE

Signal face is defined as defined as that part of a signal head provided for controlling traffic in a single direction. Turning indications may be included in a signal face. A signal face is one cluster of signal sections facing one traffic movement. A signal face has one set of red, yellow and green lamps. The signal face which is nearest to and facing the incoming traffic is called the primary signal face. A signal face showing the same indications as on a primary signal face, usually further away from the incoming traffic and on its off-side (Right) is known as secondary signal face.

• Traffic signals are control devices that alternately direct the traffic to stop and proceed at an intersection using red and green lights alternatively.
• The main requirements of traffic signals are
• to draw attention
• provide meaning and time to respond and\
• minimise wastage of time
• Traffic signals are required to
• Reduce delay
• Improve safety
• Help low volume roads
• Ensure orderly flow of traffic and
  
• Reduce the frequency of accidents
• Conflicting traffic movements make roadway intersections unsafe for vehicles and pedestrians
• Intersections are a major source of crashes and vehicle delay
• Traffic volumes and crash frequency/severity require installation of traffic signals

ADVANTAGES OF TRAFFIC SIGNALS

• Traffic signals ensure orderly movement of traffic in all directions
• Traffic signals provide a progressive flow of traffic in a signal-system corridor
• By virtue of traffic signals, side-street vehicles can safely enter the traffic stream
• Traffic signals enable pedestrians to cross the street safely
• Traffic signals have the potential to reduce accidents and ensure safety of all road users
• Traffic signals also ensure reduction in delays

DISADVANTAGES OF TRAFFIC SIGNALS

•  Delays due to large stop time
• Complex signal design problem
• Effects due to poorly-timed traffic signals
• Increased vehicle delay
• Increased rear-end vehicle crashes
• Disruption to traffic progression

 

Need for traffic signals

 NEED FOR TRAFFIC SIGNALS

• Traffic signs provide valuable information to drivers and other road users. 
• They represent rules that are essential for the safety of the population.
• Traffic signals help to communicate messages to drivers and pedestrians so that they can maintain order and reduce accidents. 
• Neglecting traffic signals can be dangerous or sometimes even fatal
• Most signs make use of pictures, rather than words, thus they are easy to understand and can be interpreted by people who speak a variety of languages. 
• Therefore it is important that drivers are familiar with each sign regarding what it represents
• Traffic signals are used to inform the other road users regarding the rules of driving. 
• Failing to obey traffic signals could result in a serious accident or a fine.

Visibility of road markings

VISIBILITY OF ROAD MARKINGS

Road Marking is defined as lines, patterns, words except road signs which are applied applied or attached attached to the carriageway carriageway or kerbs or to objects objects within or adjacent adjacent to the carriageway for Controlling, Warning, Guiding and Informing the road users.

• Road markings are essential as "bare roads" lead to total confusion
• Marking helps on the road to Direct, Guide and Regulate the road user
• Road Markings include all lines patterns, words & colour applied on or attached to the road surface or kerb.
• Road Marking are used to supplement message of road signs & other devices
• ƒ Marking promote road safety & ensure smooth flow of traffic
•  Road markings
• Guides & Controls traffic on a highway 
• Delineation of Traffic path and its lateral clearance from traffic hazards facilitating safe movement ƒ 
• Channelize the pedestrians pedestrians & cyclists cyclists movement movement into safe location 
• Road markings normally include longitudinal markings, transverse markings, text and symbols etc. on the road surfaces 
• Applicable to all categories of roads even on Rural roads as well
• Traffic paints are commonly used for road markings. Other materials such as road studs, cats eyes and thermoplastic strips also find their application in road markings.
• The Colours of road markings imply specific instructions as described below:
• WHITE is used for carriageway (road) markings except those indicating restrictions 
• YELLOW markings are used to signify RESTRICTIONS. 
• WHITE or YELLOW together with BLACK are used for kerb and object marking. 
•  Different Types of Road Markings are listed below
• CENTER LINES On undivided two-way roads, the centre line separates the opposing streams of traffic and facilitates their movements.
• The centre line can be a single broken line, a single continuous solid line (barrier line) , a double solid line or a combination of solid line and broken line.
  

In order to improve visibility of road markings during poor lighting conditions or at night, different types of reflective surfaces are used.

• Diffuse reflection
• Retro reflection and
• Mirror reflection

Diffuse reflection occurs when incident light beam falls on microscopically rough surface

Retro reflection is of two types and occurs when incident light beam falls on glass beads and cube corners

Mirror reflection occurs when incident light beam falls on microscopically smooth surface. In such cases, the angle of incident light beam is equal to the angle of reflected light beam

The pattern of retro reflected light from a vehicle headlight is in a cone shaped pattern

Poor night visibility of road markings is responsible for accidents at critical spots on a road.

Road markings must be visible clearly during the day or night.

As a general requirement, drivers should be able to detect road markings at a distance equivalent to a minimum of two seconds of travel time.

The visibility distance of road markings is enhanced when the when the line thickness is wider along with a higher mark to gap ratio and higher coefficient of retro-reflective luminance. This implies that larger pavement marking widths combined with higher coefficients of retro-reflectivity are used by drivers to detect the lines according to design speed of roadway

Retro-reflectivity is accomplished in pavement-marking through the use of glass beads that are partially embedded on the  surface of the marking as binding material and also spread externally during application time.

The quality of glass beads plays an important role in retro-reflectivity of pavement marking as the glass bead returns light from a vehicle headlight to the driver

Visibility distance is adversely affected by the glare coming from on-coming vehicles, dirty head lamps or windscreen (especially during rains). Moreover, the size of a glass bead can affect retro-reflectivity especially during wet conditions.

Larger glass beads have higher retro-reflectivity in dry conditions. In wet conditions, the light is scattered due to water on the beads rendering them useless. Beads of at-least 1mm thickness effective when roads are wet.

Road markings

ROAD MARKINGS

Definition

Road markings are defined as lines, patterns, words or other devices set into or attached to the carriageway or kerbs for controlling, warning, guiding and informing users. Road surface marking is any kind of device or material that is used on a road surface in order to convey official information.  The road markings are defined as lines, patterns, words or other devices, except signs, set into applied or attached to the carriageway or kerbs or to objects within or adjacent to the carriageway, for controlling, warning, guiding and informing the users. Road markings have been found to influence driver behaviour. They prevent meandering tendencies of drivers and enable the traffic to flow in a regular and predictable way in addition to avoiding accidents. The presence of enhanced road markings significantly increased driver comfort. Traffic paints are commonly used for road markings. Other materials such as road studs, cats eyes and thermoplastic strips also find their application in road markings. Road markings -

• supplement the function of traffic signs. 
• act as a psychological barrier and signify the delineation of traffic path and its lateral clearance from traffic hazards for the safe movement of traffic. 
• are essential to ensure the safe, smooth and harmonious flow of traffic.

Role of Road markings

Bare roads will lead to complete vehicular confusion. Hence markings are painted on the road to direct, guide and regulate the road user. Road markings  include all lines patterns, words and colours applied on or attached to assist the road users. Road markings promote road safety and ensure smooth flow of traffic. Sometimes, road markings are used to supplement the message of road signs and other devices. 

The essential purpose of road markings is to guide and control traffic on a highway. They supplement the function of traffic signs. The markings serve as a psychological barrier and signify the delineation of traffic path and its lateral clearance from traffic hazards for the safe movement of traffic. Hence they are very important to ensure the safe, smooth and harmonious flow of traffic. Various types of road markings like longitudinal markings, transverse markings, object markings and special markings to warn the driver about the hazardous locations in the road etc. 

The Colours of road markings imply specific instructions as described below:

• WHITE is used for carriageway (road) markings except those indicating restrictions 
• YELLOW markings are used to signify RESTRICTIONS. 
• WHITE or YELLOW together with BLACK are used for kerb and object marking. 
• Different Types of Road Markings are listed below
• CENTER LINES On undivided two-way roads, the centre line separates the opposing streams of traffic and facilitates their movements.
• The centre line can be a single broken line, a single continuous solid line (barrier line) , a double solid line or a combination of solid line and broken line.

The Divided Lines are called Lane Lines.

• Single and double solid lines, whether white or yellow, must not be crossed or even straddled. 
• They should be treated as a wall on the road . 
• Double Continuous lines are also used where visibility is restricted in both directions. Neither stream of traffic is allowed to cross the lines. 
• The Double Continuous Lines can be both in WHITE or YELLOW 
• Combination Lines On a road with two centre lines, of which one is solid and the other broken, the solid line has significance only it it is on the left side of the combination as viewed by the driver. In such a case, the driver must be careful not to cross or straddle the centre line. If the line on your side is broken, you may cross or straddle it. Overtake - but only if it is safe to do so. If the line on your side is continuous you must not cross or straddle it. 
• Stop Line. A stop line is a single solid transverse line painted before the intersecting edge of the road junction/ intersection. This line indicates where you are required to stop when directed by traffic officer, traffic light of stop sign. 
• Where a pedestrian crossing is provided, the stop line is marked before the pedestrian crossing. 
• Give Way Line is usually a double dotted line marked transversely at junctions. 
• These lines are generally supplemented by a reverse triangle give way sign painted on the road surface before the dotted lines or by a road sign installed beside the marking "Give way to traffic on the main approaching road". 
• Border Edge Lines are continuous lines at the edge of the carriageway and mark the limits of the main carriageway upto which a driver can safely venture. 
• Parking Prohibited Lines A solid continuous yellow line painted on the kerb or edge of the carriageway along with a No-parking sign indicates the extent of no-parking area. 
• YELLOW BOX JUNCTION These are yellow crossed diagonal lines within the box. The vehicles should cross it only if they have a clear space available ahead of the yellow box. In this marked area vehicles must not stop even briefly. 
• Pedestrian Crossing These are alternate black and white stripes painted parallel to the road generally known as zebra crossing. Pedestrians must cross only at the point where these lines are provided and when the signal is in their favour at controlled crossings. You must stop and give way to pedestrians at these crossings. Pedestrian crossings are marked to facilitate and give the right of way to pedestrians. 
  

Classification

The road markings are defined as lines, patterns, words or other devices, except signs, set into applied or attached to the carriageway or kerbs or to objects within or adjacent to the carriageway, for controlling, warning, guiding and informing the users. 

The road markings are classified as 

• longitudinal markings
• transverse markings
• object markings
• word messages
• marking for parkings
• marking at hazardous locations etc.

Longitudinal markings are placed along the direction of traffic on the roadway surface, for the purpose of indicating to the driver, his proper position on the roadway. 

Some of the guiding principles in longitudinal markings are:

• Longitudinal markings are provided for separating traffic flow in the same direction and the predominant color used is white. 
• Yellow color is used to separate the traffic flow in opposite direction and also to separate the pavement edges. 
• The lines can be either broken, solid or double solid. 
• Broken lines are permissive in character and allows crossing with discretion, if traffic situation permits. 
• Solid lines are restrictive in character and does not allow crossing except for entry or exit from a side road or premises or to avoid a stationary obstruction. 
• Double solid lines indicate severity in restrictions and should not be crossed except in case of emergency. 
• There can also be a combination of solid and broken lines. In such a case, a solid line may be crossed with discretion, if the broken line of the combination is nearer to the direction of travel. 
• Vehicles from the opposite directions are not permitted to cross the line. 

Different types of longitudinal markings are 

• Centre line
• Traffic lanes
• No passing zone
• Warning lines
• Border or edge lines
• Bus lane markings
• Cycle lane markings.

Centre line

Centre line separates the opposing streams of traffic and facilitates their movements. Usually no centre line is provided for roads having width less than 5 m and for roads having more than four lanes. The centre line may be marked with either single broken line, single solid line, double broken line, or double solid line depending upon the road and traffic requirements. On urban roads with less than four lanes, the centre line may be single broken line segments of 3 m long and 150 mm wide. The broken lines are placed with 4.5 m gaps as shown in the figure

On curves and near intersections, gap shall be reduced to 3 metres. On undivided urban roads with at least two traffic lanes in each direction, the centre line marking may be a single solid line of 150 mm wide as in figure

 A double solid line of 100 mm wide separated by a space of 100 mm is shown in figure below

The centre barrier line marking for four lane road is shown in figure below

Traffic lane lines

• The subdivision of wide carriageways into separate lanes on either side of the carriage way enables the driver to go straight and curbs the meandering tendency of the driver.
• Traffic lane lines eliminate confusion and facilitates turning movements.
• Traffic lane markings help in increasing the capacity of the road in addition to ensuring safety.
• The traffic lane lines are normally single broken lines of 100 mm width as shown.

No passing zones

No passing zones are established on summit curves, horizontal curves, and on two lane and three lane highways where overtaking maneuvers are prohibited because of low sight distance. It may be marked by a solid yellow line along the centre or a double yellow line. In the case of a double yellow line, the left hand element may be a solid barrier line, the right hand may be a either a broken line or a solid line . These solid lines are also called barrier lines. When a solid line is to the right of the broken line, the passing restriction shall apply only to the opposing traffic. Images for barrier lines are shown below.

Warning lines

Warning lines warn the drivers about the obstruction approaches. They are marked on horizontal and vertical curves where the visibility is greater than prohibitory criteria specified for no overtaking zones. They are broken lines with 6 m length and 3 m gap. A minimum of seven line segments should be provided. 

Edge lines

• Edge lines indicate edges of rural roads which have no kerbs to delineate the limits upto which the driver can safely venture. 
• They should be at least 150 mm from the actual edge of the pavement. They are painted in yellow or white.
• All the lines should be preferably light reflective, so that they will be visible during night also. 
• Improved night visibility may also be obtained by the use of minute glass beads embedded in the pavement marking materials to produce a retroreflective surface.

Transverse markings

• Transverse markings are marked across the direction of traffic. 
• They are marked at intersections etc. 
• The site conditions play a very important role. 
• The type of road marking for a particular intersection depends on several variables such as speed characteristics of traffic, availability of space etc. 
• Stop line markings, markings for pedestrian crossing, direction arrows, etc. are some of the markings on approaches to intersections.

Stop line

• Stop line indicates the position beyond which the vehicles should not proceed when required to stop by control devices like signals or by traffic police.
• They should be placed either parallel to the intersecting roadway or at right angles to the direction of approaching vehicles.
• A figure showing the stop line is shown below

Pedestrian crossing

• Pedestrian crossings are provided at places where the conflict between vehicular and pedestrian traffic is severe. 
• The site should be selected that there is less inconvenience to the pedestrians and also the vehicles are not interrupted too much. 
• At intersections, the pedestrian crossings should be preceded by a stop line at a distance of 2 to 3m for unsignalized intersections and at a distance of one metre for signalized intersections. 
• Most commonly used pattern for pedestrian crossing is Zebra crossing consisting of equally spaced white strips of 500 mm wide. 

A typical example of an intersection illustrating pedestrian crossings is shown below

Visibility of road markings

• Road markings are used as a means of controlling and guiding traffic
• Road markings are classified into carriage way markings and object markings
• Carriageway markings are applied to carriageways
• Object markings are applied to traffic islands, culvert headwalls, piers, abutments, etc
• Carriageway markings are of the following types
• Objects within the carriageway
• The obstructions within the carriageway such as traffic islands, raised medians, etc. may be marked by not less than five alternate black and yellow stripes. The stripes should slope forward at an angle of 45º with respect to the direction of traffic. These stripes shall be uniform and should not be less than 100 m wide so as to provide sufficient visibility.
• Objects adjacent to the carriageway
• Objects adjacent to the carriageway may pose some obstructions to the flow of traffic. Objects such as subway piers and abutments, culvert head walls etc. are some examples for such obstructions. They should be marked with alternate black and white stripes at a forward angle of 45º with respect to the direction of traffic. Poles close to the carriageway should be painted in alternate black and white up to a height of 1.25 m above the road level. Other objects such as guard stones, drums, guard rails etc. where chances of vehicles hitting them are only when vehicle runs off the carriageway should be painted in solid white. Kerbs of all islands located in the line of traffic flow shall be painted with either alternating black and white stripes of 500 mm wide or chequered black and white stripes of same width.
• Word messages
• Information to guide, regulate, or warn the road user may also be conveyed by inscription of word message on road surface. Characters for word messages are usually capital letters. The legends should be as brief as possible and shall not consist of more than three words for any message. Word messages require more and important time to read and comprehend than other road markings. 
• Examples of word messages are STOP, SLOW, SCHOOL, RIGHT TUN ONLY
• Typical dimension of the letter 'T' is shown below

Parking

• The marking of the parking space limits on urban roads promotes more efficient use of the parking spaces and tends to prevent encroachment on places like bus stops, fire hydrant zones etc. where parking is undesirable. 
• Parking space limitations should be indicated with markings that are solid white lines 100 mm wide. Words TAXI, CARS, SCOOTERS etc. may also be written if the parking area is specific for any particular type of vehicle. 
• To indicate parking restriction, kerb or carriage way marking of continuous yellow line 100 mm wide covering the top of kerb or carriageway close to it may be used.

Hazardous location

• Wherever there is a change in the width of the road, or any hazardous location in the road, the driver should be warned about this situation with the help of suitable road markings. 
• Road markings showing the width transition in the carriageway should be of 100 mm width. 
• Converging lines shall be 150 mm wide and shall have a taper length of not less than twenty times the off-set distance. 
• Typical carriageway markings showing transition from wider to narrower sections and vice-versa is shown in figure below

Road markings are aids to control traffic by exercising psychological control over the road users. They are made use of in delineating the carriage way as well as marking obstructions, to ensure safe driving. They also assist safe pedestrian crossing. Longitudinal markings which are provided along the length of the road and its various classifications were discussed. Transverse markings are provided along the width of the road. Road markings also contain word messages, but since it is time consuming to understand compared to other markings there are only very few of them. Markings are also used to warn the driver about the hazardous locations ahead. Thus road markings ensure smooth flow of traffic providing safety also to the road users.

The standard to be followed with regard to paint arrows as road markings with dimensions is shown in the figure below:

Sign Variables

SIGN VARIABLES or VARIABLE MESSAGE SIGNS

Variable Message Signs (VMS) are used to inform and direct motorists of variable situations in a consistent and orderly manner. The messages are meant for:

• Traffic control
• Management and
• Timely traveller information

Critical aspects of these traffic control devices are:

• Legibility
• Reliability and
• Credibility

Signs are the primary means of communicating with the motorists.The information is displayed real-time and can be controlled on-site or from a remote centralized location.

• The signs are designed to modify motorist behaviour to improve traffic flow and operations.
• Information for travellers is displayed due to a planned or unplanned event which is scheduled by operations personnel.
• They are commonly installed on full span overhead sign bridges, post-mounted roadway on shoulders, overhead cantilever structures and portable types mounted on trailers/prime-mover.
• Below are a few examples on information provided through VMS
• Travel time between known destinations
• Congestion conditions along a high-speed corridor
• Construction site warnings / Information notices
• Special event notice and motorist instructions
• Maintenance operations schedule
• Severe weather announcement
• Incident or accident information
• For all information displayed, the goal is to have a positive impact on the motorist's travel time
• The system comprises of continuous and discontinuous signs
• Variable Message Signs (VMS) used for dynamic traffic management are of discontinuous type and make use of ligh emitting techniques (Ex: Fiber optic or LED signs)
• VMS for a part of Advanced Traffic Management System (ATMS) which is one of the major components of ITS (Intelligent Transport System)
• The integrated ATMS software receives online data from Automatic Traffic Counter and Classifier (ATCC), meteorological sensors, Traffic Control System, CCTV, Video Incident Detection System (VIDS), Emergency Call Boxes (EBC), etc.
• This data is processed and analysed. The information is then shared with road users through VMS, SMS, FM, radio, etc.

Sign Visibility

SIGN VISIBILITY

• Sign visibility refers to the likelihood of a sign being found in the driving environment and is integrally associated  with sign conspicuity. 
• Sign conspicuity is a function of a sign’s capacity to attract a driver’s attention that depends on sign, environmental, and driver variables Sign legibility describes the ease with which a sign’s textual or symbolic content can be read. 
• Sign legibility differs from sign recognizability in that the former refers to reading unfamiliar messages while the latter refers to identifying familiar sign copy. 
• Sign legibility and recognizability in turn differ from sign comprehensibility in that the latter term implies understanding the message while the former merely involve the ability to discern critical visual elements.
• Other measures of sign visibility include blur tolerance and comprehension speed
• Sign visibility is most often assessed by determining threshold distance. 'T'
• The two thresholds used are 
• Detection distance (the distance at which an observer can find a sign in the driving environment) and
• Legibility distance (the distance at which an observer can read a sign’s message).
•  The intent of a sign designer is to provide the sign’s observer with the maximum time to read the sign, and to do that the observer must find it before its maximum reading distance.
• Legibility index (LI) refers to the legibility distance of a sign as a function of its text size

Measures of sign effectiveness

 MEASURES OF SIGN EFFECTIVENESS

• Traffic signs are constantly evaluated for their effectiveness in preventing accidents with other vehicles, pedestrians and infrastructure (Government or private property).
• Evaluations are done based on field observation of pedestrian and driver behaviour before and after installation of countermeasures at specific locations selected on the basis of frequency of accidents observed. 
• A statistically significant improvement has been reported in case of driver behaviour and pedestrian habits at locations wherever such countermeasures were adopted.
• Signs and markings are used to control and guide traffic and to promote road safety.
• The quality of its traffic signs and markings make a significant contribution to road safety.
• To be effective, signs and markings must be designed and implemented in a way that the messages they convey are clear, unambiguous, visible and legible. 
• At the same time these should give warning to drivers and road users with sufficient time to respond safely. 
• Maintenance of signs and markings is important. 
• Distraction can also be caused by looking for a sign that may be missing. Therefore, continuity of directional signing is important. Young (age 17-21) drivers are particularly prone to external-to-vehicle driver distraction caused by signs. 
• New generations of traffic signs based on electronic displays can also change their text (or symbols) to provide for "intelligent control" linked to automated traffic sensors
• Real-time Traffic Message Channel incident warnings are conveyed directly to vehicle navigation systems using signals carried via FM radio, 3G cellular data and satellite broadcasts
• Confusion of drivers, misunderstanding or lack of familiarity with traffic control devices can lead to accidents
• It has been demonstrated that supplemental 'text' information along with a symbol has shown a marked improvement over usage of only symbols
• Replacement of existing signs with signs that are easier to understand improves the effectiveness of signs. This is done by evaluating the drivers response to an accident prone area with a particular sign.
• Driver education and driver improvement programs are positive predictors of knowledge of traffic controls.
• Effectiveness of traffic signs should be directed towards the driving public by making use of public service announcements and educational campaigns.
• The effectiveness of a traffic control to a large extent depends on conspicuity as determined by brightness contrast, primarily the similarity of the control device relative to its surroundings.
• The probability of seeing a traffic sign or pavement marking is lessened with increased experience in driving, and each type of sign has a specific rate of decline.
• Signal value is determined by the probability of punishment for disobedience of the traffic control. 
• Speed limit signs have been found to have a high signal value, which is a result of the motorist's awareness of constant enforcement efforts. 
• Other signs which are less frequently enforced would be expected to have a lower signal value, in spite of the fact that violation of these signs may prove more hazardous.
• Level of exposure refers to the number of times the driver has read the communication before.
• Length of exposure refers to the viewing time of the recipient.
• Both level and length of exposure are salient variables affecting the motorist 1 s information processing capability.
• In daily situations, many motorists simply "ride with the tide" of traffic or stay in the traffic flow, unable to independently navigate the roadway.
• Education regarding traffic controls, in the form of driver education, defensive driving, and informal education, has a direct effect on correct identification of traffic signs.
• Understanding of specific signs has been found to be a function of education level, driving experience, driver education, age, and several other factors
• It has been proved by field studies that drivers with the highest level of understanding had taken a driver education course
• The STOP sign is not as widely recognized as would be expected by its unique shape and color. The word 'stop' must be visible on the sign to be identified by the driving population
• Similarly, was the case for "YIELD" and "DO NOT ENTER" signs. Hence, it is imperative to write TEXT along with the symbol.