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.