Traffic lights

TRAFFIC MANAGEMENT TECHNIQUE - TRAFFIC LIGHTS

• Traffic management is a key branch within logistics. 
• It concerns the planning, control and purchasing of transport services needed to physically move vehicles and freight.  
• Traffic management refers to the organisation, arrangement, guidance and control of both stationary and moving traffic, including pedestrians, bicyclists and all types of vehicles.
• The aim of traffic management is to provide for the safe, orderly and efficient movement of persons and goods, and to protect and, where possible, enhance the quality of the local environment on and adjacent to traffic facilities.
• Traffic lights form an important aspect of traffic management and are essential for effective flow of  vehicles on a road network

Safety Cameras

USE OF SAFETY CAMERAS FOR TRAFFIC MANAGEMENT

A CCTV system is a closed video system where the signal is transmitted to a limited set of monitors, restricting the view to a certain set of people with specific purposes. Closed circuit television (CCTV) refers to the use of video cameras to transmit signals to a specific place with a set of monitors. Traffic control is becoming a critical application for CCTV. A typical CCTV system is composed of a camera system, reviewing displays and a central controller.

• CCTV provides a way to monitor multiple cameras internally and analyse generated images to extract useful information about traffic parameters, such as 
• speed
• traffic composition
• vehicle shapes
• vehicle types
• vehicle identification numbers and 
• occurrences of traffic violations or road accidents. 
• This offers a great help for transportation authorities, allowing them to make decisions accordingly and distribute traffic information to drivers, resulting in 
• improved traffic flow
• prompt accident detection
• shorter journey time
• less fuel consumption
• reduced emissions and 
• more satisfied travelers
• In the context of vehicles traffic management, there are two different perspectives to be considered
• the driver’s perspective and 
• the traffic authority’s perspective.
• `By studying reoccurring traffic patterns and trends, it is possible to learn how they are formed and why.
• Image-based CCTV systems have the ability to recognise unusual and abnormal events on roads by analysing digital images and extracting traffic parameters such as speed and traffic composition. Special software tools are usually used to help in recognising vehicle shapes, vehicle types, vehicle identification numbers and occurrence of traffic violations or road accidents.
• Automatic Number Plate Recognition (ANPR) system as an example of such tools
• After processing captured data and detecting an incident, two different approaches are available in the literature to implement the system reaction:
• Manual reaction and
• Automatic reaction
• CCTV leads to better traffic control.
• However, CCTV systems are extremely costly to install and operate and are offensive to privacy
• CCTV systems are increasingly used for road monitoring and traffic control systems. 
•  The computer analysis process of CCTV data is important to reduce errors and cost in terms of time and money.

Speed and load limit

Speed and load limit

Speed limit is defined as the maximum speed at which a vehicle is legally permitted to travel, as within a specific area, on a certain road, or under given conditions. Roads of different categories and under different situtions are designed for designated design speeds at which vehicles can travel with convenience and safety. 

However, at certain locations, such as approaches to manned and unmanned level crossings, sharp curves, congested/accident-prone locations, residential streets, etc., control of speed may become necessary to promote orderly traffic movement and improved safety.

Speed management can be defined as a set of measures to limit the negative effects of excessive and inappropriate speeds. Not only does this mean measures to restrict speed, but it also includes elements of road design, separation of different types of road users, road markings etc. based on the volume and type of traffic on that particular road. One of the most important aspects of speed management is education of road users.
The advantages and disadvantages of higher speeds, and why speeds should be low in urban areas

Advantages
• Allows reduction of journey time
• Enhances mobility
• Caters to driver's adrenalin rush & entertainment (questionable advantage)

Disadvantages
• Increases the distance travelled before a driver's reaction time + stopping distance can stop a vehicle
• Increases fuel consumption
• Increases greenhouse gas emissions
• Lesser time for both driver and other road users to recognize

Hazards
• Reduced ability of other road users to judge vehicle speed and time before collision
• Lesser opportunity for other road users to avoid a collision
• Greater likelihood that a driver will lose vehicle control
• Adversely impacts quality of life of vulnerable road users

LOAD LIMIT

Load limit sign on the road indicates the load of the vehicle, which should ply on the road. Overloading has been recognized to be both a safety concern as well as a cost concern. Overloaded vehicles, especially freight vehicles, destroy roads and negatively impact economic growth. The damage caused grows exponentially as the load increases. Damage to roads as a result of overloading leads to higher
maintenance and repair costs and shortens the life of a road which in turn places an additional burden on the government as well as law-abiding road users who ultimately carry the costs of inconsiderate
overloading. 

If the problem of overloading is not controlled, this cost has to be carried by the road user, which will require significant increases in road user charges such as the fuel tax, vehicles license fees, and overloading fees. Overloading is a safety hazard that leads to unnecessary loss of life, and also the rapid
deterioration of our roads, resulting in increased maintenance and transportation costs.
Overloaded vehicles threaten road safety and are contribute to many of the fatal accidents on roads. The overloaded vehicle will not only put the driver at risk but also passengers and other road users.
The following are the risks of overloading vehicles:

• The vehicle will be less stable, difficult to steer and take longer to stop. 
• Vehicles react differently when the maximum weights which they are designed to carry are exceeded.
• Overloaded vehicles can cause the tyres to overheat and wear rapidly which increases the chance of premature, dangerous and expensive failure or blow-outs.
• The driver’s control and operating space in the overloaded vehicle are diminished, escalating the chances of an accident.
• The overloaded vehicle cannot accelerate as normal – making it difficult to overtake
• At night, the headlights of an overloaded vehicle will tilt up, blinding oncoming drivers to possible debris or obstructions on the roadway
• Brakes have to work harder due to ‘the riding of brakes’ and because the vehicle is heavier due to overloading. 
• Brakes overheat and lose their effectiveness to stop the car.
• Due to overloading of passenger vehicles, seat belts are often not used as the aim is to pack-in as many persons as possible into the vehicle
• The whole suspension system comes under stress and, over time, the weakest point can give way.
• By overloading your vehicle you will incur higher maintenance costs to the vehicle – tyres, brakes, shock absorbers and higher fuel consumptionInsurance cover on overloaded vehicles may be void as overloading is illegal
  

The following measures are suggested to counter overloading

• A strategy map that will assist planners in deciding on appropriate locations for additional weighbridges.
• A database containing information on weighbridge operations and monitoring, as well as monthly reports that will be accessible via a website.
• This database will also contain information on habitual offenders.
• Portable scales are in the process of being evaluated, determining their accuracy and acceptability for prosecution purposes. 
• Legislation to extend the responsibility of overloading to the consigner and the consignee is in the process of being drafted.
• Vehicle testing stations are equipped with state-of-the-art testing equipment such as break rollers to test the quality of a vehicle’s breaks, a scuff gauge to measure the wheel alignment and many others.  
• This is done to ensure that when a vehicle is certified as being roadworthy it will definitely meet the prescribed standards.
• The National Roads Agency can enter into performance-based agreements with the private sector for the operation and administration of the weighbridges, and service agreements with the Local Traffic Authorities in order to ensure a dedicated attack on overloading.
• The strategy includes the monitoring and weighing of vehicles attempting to bypass the weighbridges by using alternative routes.

Integrated safety improvement and Traffic calming schemes

INTEGRATED SAFETY IMPROVEMENT

 The objectives of traffic management schemes is the development of a systematic process along with the various techniques that may be used for traffic management are described. The application of traffic management techniques to rural and urban roads is discussed. This includes treating routes or networks as a whole rather than simply focussing on isolated problem spots. 

Past and likely future trends in road travel along with various techniques for travel demand management are addressed.
Traffic management should be logically applied and consistently enforced, or it will not be effective. Enforcement must be considered an integral part of traffic management.

Integrated safety improvement

Integrated safety improvement is an integral part of reducing traffic fatalities. Traffic accidents contribute significantly to the annual social cost of a country's GDP. A direct consequence of economic
development is rapid motorization. The traffic police play a very important role in reducing traffic fatalities by road policing, traffic management and traffic enforcement, accident investigation, accident reporting and analysis, driver licensing, vehicle registration and traffic education. The five pillars on which road safety, traffic enforcement policies and actions are built are:

• Road safety management
• Safer roads
• Safer vehicles
• Safer road users and
• Post crash care
  

A few efforts to impart a positive influence on road safety are listed below:

• Establishment of a lead road safety agency at national & state levels that is equipped with the power, expertise and capacity to carry out the necessary activities independently.
• Notify legislations with regard to helmets, seat belts, drinking and driving, speeding, day time running lights and use of cell phones on an urgent basis in all Indian states.
• Establish a dedicated and ring–fenced road safety fund at national and state levels to cover all road safety initiatives.
• Mandate road safety audits for all new and existing roads from the designing stage itself.
• Create a Motor Vehicle Accident Fund to provide compulsory insurance for all road users
• Standardize, regulate, and enforce vehicle safety requirements.
• Build capacities across various sectors—police, health, and transport-- at central and state levels
• Establish Centres of excellence in road safety that can work towards road safety by undertaking capacity building, training, research and monitoring.
• Adopt the principle of safe systems approach for design of all new roads in such a way that road design should be forgiving.
• Strengthen road safety information systems to obtain reliable, robust and good quality data to guide all road safety activities. 
• For this purpose, data through the newly introduced road accident data collection formats should be strengthened at district and state levels with technical inputs.
  

Traffic calming schemes

• Traffic calming is a way of containing vehicle speeds by self-enforcing engineering measures and improving driver behaviour.
• Traffic calming has proved to be effective in restricting vehicle speed and in reducing the number and severity of road accidents, particularly in residential areas.
• Traffic calming uses physical design and other measures to improve safety for motorists, pedestrians and cyclists.
• It has become a tool to combat speeding and other unsafe behaviours of drivers in the neighbourhoods.
• The aim of implementing traffic calming measures is to encourage safer, more responsible driving and potentially reduce traffic flow
• Urban planners and traffic engineers have many strategies for traffic calming such as
• narrowed roads and
• speed humps
• The three "E's"that traffic engineers refer to  when discussing traffic calming are:
• Engineering
• (community) Education, and 
• (police) Enforcement
• Residents of a community often contribute to the perceived speeding problem within their neighborhoods.
• Hence, instructions on traffic calming; stress that the most effective traffic calming plans entail all three components and engineering measures alone will not produce satisfactory results.
• Engineering measures involve physically altering the road layout or appearance to actively or passively retard traffic any of the following techniques:
• increasing the cognitive load of driving 
• increasing the chance than an obstruction in the road will slow or momentarily stop motorists
• increasing the chance of passenger discomfort or even
• physical damage to a vehicle if speed limits are not observed (such as speed humps).
• especially designated areas where cyclists and pedestrians have legal priority over cars
• several visual changes to roads are made to encourage more attentive driving, reduced speed, reduced crashes, and a greater tendency to yield to pedestrians. 
• Visual traffic calming includes lane narrowings, road diets, use of trees next to streets, on-street parking and buildings placed in urban fashion close to streets.
• Physical devices include speed humps, speed cushions and speed tables, sized for the desired speed. Such measures normally slow cars to between 16 and 40 km/h.
• Traffic calming devices are made of asphalt or concrete. However, traffic calming products made of rubber are emerging as an effective alternative with several advantages.
• Traffic calming can include the following engineering measures:
• Narrowing: Narrowing traffic lanes makes slower speeds seem more natural to drivers and are less intrusive than other treatments that limit speed or restrict route choice. Narrowing measures include:
• Lane narrowings can be created by extending sidewalks, adding bollards or planters, or adding a bike lane or on-street parking.
• Kerb extensions (also called bulbouts) narrow the width of the roadway at pedestrian crossings
• Chokers are kerb extensions that narrow roadways to a single lane at certain points
• Road diets remove a lane from the street. For example, allowing parking on one or both sides of a street to reduce the number of driving lanes.
• Pedestrian refuges or small islands in the middle of the street can help reduce lane widths.
• Converting one-way streets into two-way streets forces opposing traffic into close proximity, which requires more careful driving.
• Construction of polymer cement overlay to change asphalt to brick texture and colour to indicate a high-traffic pedestrian crossing.
• Vertical deflection: Raising a portion of a road surface can create discomfort for drivers travelling at high speeds. Both the height of the deflection and the steepness affect the severity of vehicle displacement. Vertical deflection measures include:
• Speed bumps, sometimes split or offset in the middle to avoid delaying emergency vehicles
• Speed humps, parabolic devices that are less aggressive than speed bumps.
• Speed cushions, two or three small speed humps sitting in a line across the road that slow cars down but allows wider emergency vehicles to straddle them so as not to slow emergency response time.
• Speed tables, long flat-topped speed humps that slow cars more gradually than humps
• Raised pedestrian crossings, which act as speed tables, often situated at junctions.
• Speed dips, sunken instead of raised 
• Changing the surface material or texture (for example, the selective use of brick, cobblestone, or polymer cement overlay).
• Changes in texture may also include changes in color to highlight to drivers that they are in a pedestrian-centric zone.
• Rumble strips, when placed perpendicular to traffic in the travel lane act as speed bumps as they produce unpleasant sounds and vibration when crossed at higher speeds.
• Horizontal deflection, i.e. make the vehicle swerve slightly. These include:
• Chicanes, which create a horizontal deflection that causes vehicles to slow as they would for a curve.
• Pedestrian refuges again can provide horizontal deflection, as can kerb extensions and chokers.
• Block or restrict access. Such traffic calming means include:
• Median diverters to prevent left turns or through movements into a residential area.
• Converting an intersection into a cul-de-sac or dead end.
• Boom barrier, restricting through traffic to authorised vehicles only.
• Closing of streets to create pedestrian zones.
• Enforcement and education measures
• Enforcement and education measures for traffic calming include:
• Reducing speed limits near institutions such as schools and hospitals (see below)
• Vehicle activated sign, signs which react with a message if they detect a vehicle exceeding a pre-determined speed.
• Embedded pavement flashing-light systems which react to pedestrian presence at crossings to signal drivers and increase awareness.
• Watchman, traffic calming system
• Speed reduction has traditionally been attempted by the introduction of statutory speed limits. Traffic speeds of 30 km/h and lower are said to be more desirable on urban roads with mixed traffic. 
• Zones where speeds are set at 30 km/h are gaining popularity as they are found to be effective at reducing crashes and increasing community cohesion.
• Speed limits which are set below the speed that most motorists perceive to be reasonable for the given road require additional measures to improve compliance. 
• Attempts to improve speed limit observance are usually by either education, enforcement or road engineering. 
• "Education" refers to targeted road user training.
• Speed limit enforcement techniques include: 
• direct police action
• automated systems such as speed cameras or vehicle activated signs or traffic lights triggered by traffic exceeding a preset speed threshold. 
• Cyclists argue for placing direct restrictions on motor-vehicle speed and acceleration performance.
• Reports on promoting walking and cycling specify use of comprehensive camera-based speed control using mainly movable equipment at unexpected spots as one of the top measures .
• Advanced countries have an estimated 1,500 speed/red-light camera installations and set a target for 30 km/h limits on 70% of urban roads.

Traffic management

 Traffic management

Traffic management is the organisation, arrangement, guidance and control of both stationary and moving traffic, including pedestrians, bicyclists and all types of vehicles. Its aim is to provide for the safe, orderly and efficient movement of persons and goods, and to protect and, where possible, enhance the quality of the local environment on and adjacent to traffic facilities. For effective traffic management, it is essential that the practitioner works from factual information. Road inventory and statistical methods, and the more common types of traffic studies, including traffic volume and composition, origin and destination, speed, travel time and delay, accidents and parking are essential.  "Before and after" studies, and estimation of future traffic are also considered. In order to apply traffic management techniques logically, it is necessary to develop a classification or hierarchy of all roads to ensure that the primary purpose of each of them is defined, agreed and understood. The various aspects of traffic management include signing and delineation, pedestrian facilities, bicycle facilities, intersections, traffic signals, road capacity, parking, roadside safety and roadway lighting.

Solutions to design of traffic signals

SOLUTIONS TO PROBLEMS ON 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

        Solution:

Total time lost = tL = 2 + 1 = 3 seconds

Effective green time = gi= 27 + 4 - 3 = 28 seconds

 As per the equation for saturation flow rate = Si = 3600 / h = 3600/2.4 

                                                                        = 1500 vehicles / hour

Capacity of the given phase is found by the equation Ci = 1500 * (28/60)

                                                                                        =    700 vehicles/hour/lane

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 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. on the two approaches of road-1 and 278 and 189 PCU/hour on the two approaches of road-1 and 278 and 180 PCU.hour on the two approaches of road-2. Design the signal timing as per IRC guidelines

Solution

Width of road-1 = 12.0m, 4 lanes = 2 lanes in each direction

Width of road-2 = 6.6m, 2 lanes = 1 lane in each direction

Approach volume on road-1 = 90 & 743 PCU/hr

Approach volume on road-2 = 278 & 180 PCU/hr

Pedestrian walking speed = 1.2m/s

Design traffic on road-1 = higher of the two approach volume per lane

                                        =    900/2 = 450PCU/hr

Design traffic on road-2 = 278 PCU/hr

STEP-1

Pedestrian crossing time

Pedestrian green time for road-1 = (12/1.2) + 7.0 = 17 seconds

Pedestrian green time for road-2 = (6.6/1.2) + 7.0 = 12.5 seconds

STEP-2

Minimum green time for traffic

Minimum green time for vehicles on road-1 = G(i) = 17 seconds

Minimum green time for vehicle on road-1 = G1 = 17 * (450/278) = 27.5 seconds

STEP 3

Revised green time for traffic signals

Adding 2.0 seconds each towards clearance amber and inter-green period for each phase, total cycle time required = (2 + 17 + 2) +(2 + 27.5 + 2) = 52.5 seconds

Approximating this to the next multiple of 5, cycle time = 55 seconds

Signal time is set conveniently in multiples of 5

The extra time of (55 - 52.5) may be apportioned to green times of road-1 and road-2 as 1.5 and 1 seconds respectively. Adopting G1 = 27.5 + 1.5 = 29.0 seconds and G2 = 17.0 + 1.0 = 18 seconds

STEP 4

Checking for clearing the vehicles during the green phase

Vehicle arrival per lane per cycle on road-1 = (450/55) = 8.2 PCU/cycle

Minimum green time required per cycle to vehicles on road-1 =

                     = 6 + (8.2 - 1.0) * 2 = 20.4 seconds (This is less than 29 seconds, hence accepted)

Vehicle arrival per lane per cycle on road-2 = (278/55) = 5.1 PCU/cycle

Minimum green time required per cycle to vehicles on road-2 =

                     = 6 + (5.1 - 1.0) * 2 = 14.2 seconds (This is less than 18 seconds, hence acceptable)

Since the green time provided by the road by pedestrian crossing criteria is higher than the values calculated, the design values are correct

STEP 5

Check for optimum signal cycle by webster's equation 

Lost time per cycle = (amber time + inter-green period + time lost for initial delay of first vehicle) for two phases. = (2 + 2 + 4) *2 = 16 seconds

Saturation flow for road-1 of width 6 m = 525 * 6 = 3150 PCU/hour

Saturation flow for road-2 of width 3.3 m = 180 PCU 3.0 wide road + (40 * 3/5)

                                                                    = 1874 PCU/hour

y1 = 900 / 3150 = 0.286 & y2 = 278/1874 = 0.148

Optimum cycle time  C0 = (1.5L + 5)/(1 - y) = 51.2 seconds

Hence, cycle time of 55 seconds as designed earlier is acceptable. The details of signal timing are tabulated as follows.

                                                                                                                                      

Road        Green phase        Amber time        Red phase        Cycle time

Road-1            29 s                            2 s                      (22 + 2)                55

Road-2            18 s                            2 s                       (33 + 2)                55

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3.    Average speed on a roadway = 80 kmph

       Average spacing between vehicles (under stopped conditions) = 6.9m

        Maximum flow of vehicles (C) = 100 * Average Velocity / Stopping distance

                                                           =    100 * (80/6.9)

                                                            =    1159.42 vehicles/hour

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4.    15-minute traffic counts n1= 178 and n2= 142

        A1= 3 sec, A2= 2 sec, Ht= 2.5 sec

        Trial (i) Assume a trial cycle C1= 50 sec

        Number of cycles in 15 min = 15 * 60/50 = 18 sec

        Green time for Road-1, allowing average time headway of 2.5 sec per                 vehicle,G1= 178×2.518= 24.7 sec

        Similarly for Road-2, G2= 142×2.518= 19.7 sec

        Amber times A1 and A2 are 3 and 2 sec (given) 

        Total cycle length, C = (G1+ G2+ A1+ A2)= 24.7 + 19.7 + 3.0 + 2.0 

                                            = 49.4 sec

As this is lower than the assumed trial cycle of 50 sec, another lower cycle length may be tried.

Trial (ii)

Assume a trial cycle C2= 40 sec

Number of cycles in 15 min = 15 * 60/40 = 22.5sec 

Green time for Road-1, allowing average time headway of 2.5 sec per vehicle, G1= 178×2.522.5= 19.8 sec 

Similarly for Road-2, G2= 142×2.522.5= 15.8 sec 

Amber times A1and A2are 3 and 2 sec (given) 

Total cycle length, C = (G1+ G2+ A1+ A2)= 19.8 + 15.8 + 3.0 + 2.0=  40.6 sec

As this is lower than the assumed trial cycle of 50 sec, another higher cycle length may be tried. 

Trial (iii)Assume a trial cycle C3= 45 sec 

Number of cycles in 15 min = 15*60 / 45= 20sec

Green time for Road-1, allowing average time headway of 2.5 sec per vehicle,G1= 178×2.5/20= 22.25 sec

Similarly for Road-2, G2= 142×2.5/20= 17.75 sec

Amber times A1and A2are 3 and 2 sec (given)

Total cycle length, C = (G1+ G2+ A1+ A2)

                                    = 22.25+17.75+3.0+2.0= 45.0 sec

Therefore, the trial cycle of 45 sec may be adopted with the following signal phases: 

G1= 22.25, say adopt G1= 22 sec 

G2= 17.75, say adopt G2= 18 sec

 Adopt A1= 3 sec, A2= 2 sec

Total cycle length, C = (G1+ G2+ A1+ A2)= 22.0 + 18.0 + 3.0 + 2.0= 45.0 sec 

 Since this is greater than the assumed cycle of 40 seconds, the value of 45 seconds of cycle time is adopted.

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 5.    Flow of traffic on road A = 400 PCU/hour

        Flow of traffic on road B = 250 PCU/hour

        Saturation flow value on road A =1250 PCU/hour

        Saturation flow value on road B =1000 PCU/hour

         Pedestrian crossing time = 12 seconds

Using WEBSTERs method to design traffic signal

Normal flow on roads A & B in PCU/hr

Saturation flow

All – red time, R=12 sec

Number of phase, n = 2 

Total lost time in sec 

Optimum cycle time say (~ 67.5 sec)

Providing an all-red time, R for pedestrian crossing = 12 sec

Providing Amber times of 2.0 sec each for clearance

Total cycle time = 29 + 22.5 + 12 + 2 + 2 = 67.5 sec.

Width of road – 1 = 12.0 m or total 4 lanes, with 2 lanes in each direction; Width of road - 2 = 6.6 m or total 2 lanes, with one lane in each direction. Approach volumes on road – 1 = 900 & 743 PCU/hr On road - 2 = 278 & 180 PCU/hr Pedestrian walking speed = 1.2 m/sec. Design traffic on road - 1= higher of the two approach volume per lane = 900/2 = 450 PCU/hr Design traffic on road – 2 = 278 PCU/hr Step – 1. Pedestrian crossing time Pedestrian green time for road – 1 = sec Pedestrian green time for road – 2 = sec Step – 2, Minimum green time for traffic Minimum green time for vehicles on Road – 1, G (1) = 17 sec Minimum green time for Road – 1, sec = 

revised green time for traffic signals Adding 2.0 sec each towards clearance amber and 2.0 sec inter-green period for each phase, total cycle time required = (2 + 17 + 2) + (2 + 27.5 + 2) = 52.5 sec. Signal cycle time may be conveniently set in multiples of five sec and so the cycle time = 55 sec. The extra time of 55.0 – 52.5 = 2.5 sec per cycle may be apportioned to the green times of Road – 1 and Road – 2, as 1.5 and 1.0 sec respectively. Therefore adopt sec and sec Step – 4, check for clearing the vehicles arrived during the green phase Vehicle arrivals per lane per cycle on Road – 1 = 450/55=8.2 PCU/cycle Minimum green time required per cycle to clear vehicles on Road – 1 = 6 + (8.2 – 1.0)2 = 20.4 sec (less than 29.0 sec and therefore accepted) Vehicle arrivals per lane per cycle on Road – 2 = 278/55 = 5.1 PCU/cycle Minimum green time for clearing vehicles on Road – 2 = 6 + (5.1 - 1.0) 2 = 14.2 sec(less than 18.0 sec) As the green time already provided for the two roads by pedestrian crossing criteria in Step (2) above are higher than these values (29.0 and 18.0 sec), the above design values are alright.

check for optimum signal cycle by Webster’s equation Lost time per cycle = (amber time + inter – green time + time lost for initial delay of first vehicle) for two phases = (2 + 2 + 4) x 2 = 16 sec. Saturation flow for Road – 1 of width 6 m = 525 x 6 = 3150 PCU/hr Saturation flow for Road – 2 of width 3.3 m =1850 PCU for 3.0 m wide road + ( 40 * 3/5) = 1874 PCU/hr Y = 0.286 + 0.148 = 0.434 Optimum signal cycle time, sec Therefore the cycle time of 55 sec designed earlier is acceptable. The details of the signal timings are given below. These may also be shown in the form of phase diagram as in Fig. 5.30. Road Green phase, G sec Amber time, sec Red phase, R sec Cycle time, C sec Road 1 29 2 (22 + 2) 55 Road 2 18 2 (33 + 2) 55 

APPROXIMATE METHOD BASED ON PEDESTRIAN CROSSING REQUIREMENT 

The following design procedure is suggested for the approximate design of a two phase traffic signal unit at cross roads, along with pedestrian signals: 

Based on pedestrian walking speed of 1.2 m per second and the roadway width of each approach road, the minimum time for the pedestrian to cross each road is also calculated

Total pedestrian crossing time is taken as minimum pedestrian crossing time plus initial interval for pedestrians to start crossing, which should not be less than 7 sec and during this period when the pedestrian will be crossing the road, the traffic signal shall indicate red or ‘stop’.

The red signal time is also equal to the minimum green time plus amber time for the traffic of the cross road.

The actual green time needed for the road with higher traffic is then increased in proportion to the ratio of approach volumes of the two roads in vehicles per hour per lane. 

Based on approach speeds of the vehicles, the suitable clearance interval between green and red period i.e., clearance amber periods are selected.

The amber periods may be taken as 2, 3 or 4 seconds for low, medium and fast approach speeds

The cycle length so obtained is adjusted for the next higher 5 – sec interval; the extra time is then distributed to green timings in proportion to the traffic volumes The timings so obtained are installed in the controller and the operations are then observed at the site during peak traffic hours; modification in signal timings are carried out if needed

The design of a simple two-phase signal is given below.

1.   Example - 4 An isolated traffic signal with pedestrian indication is to be installed on a right angled intersection with road A, 18 m wide and road B, 12 m wide. During the peak our, traffic volume per hour per lane of road A and road B are 275 and 225 respectively. The approach speeds are 55 and 40 kmph, on roads A and road B respectively. Assume pedestrian crossing speed as 1.2 m per sec. Design the timings two-phase traffic and pedestrian by the approximate method. Solution Given: Widths of road A = 18 m and of road B = 12 m Traffic volumes on road A = 275 and on road B = 225 vehicles/lane/hour Approach speeds on road A = 55 and on road B = 40 kmph Pedestrian crossing speed = 1.2 m/sec Design of two-phase traffic control signals Pedestrian crossing/clearance time for Road A = 18/1.2 =15 sec Pedestrian crossing/clearance time for Road B = 12/1.2 = 10 sec Adding 7 sec initial walk period, minimum red time for traffic of road A, is (15 + 7) = 22 sec and that for road B is (10 + 7) = 17 sec. Minimum green time, for traffic of road B, based on pedestrian crossing requirement = 22-3 = 19 sec. Minimum green time, for traffic of road A, based on pedestrian crossing requirement = 17- 4= 13 sec. 
2. The minimum green time calculated for road A is with respect to pedestrian crossing time required for the narrower road B.  As road A has higher traffic volume per lane than road B, the green time of road A has to be higher than that of road B;  the increase may be proportion to the approach volume of road A with respect to that of road B. Let and be the green times and be the approach volume per lane Using the relation, Green time for traffic is taken as the minimum value = 19 sec as obtained from pedestrian crossing criterion for the wider road A. Green time for traffic of road A may be increased in proportion to higher traffic volume Using relation sec Based on the approach speed of 55 kmph for road A, amber period, sec For road B with 40 kmph, amber period, sec Total cycle length Therefore adopt signal cycle length of 50 sec. The additional period of 50 – 49.2 = 0.8 sec is distributed to green timings in proportion to the approach traffic volume. Therefore the revised signal phase are: sec, adopt 23.5 sec sec, adopt 19.5 sec Therefore cycle time, C = 23.5 + 19.5 + 4 + 3 = 50 sec
3. Design of pedestrian signals: Do not Walk (DW) period of pedestrian signal at road A (is red period of traffic signal at B). Pedestrian clearance intervals (CI) are of 15 and 10 sec respectively, for roads A and B for crossing. The walk time (W) is calculated from total cycle length.

Design of traffic signal problem

 Design a traffic signal for the following right angled intersection

• Major street = 12 m (4 lanes)
• Minor street = 6 m (2 lanes)
• The peak hour volumes in each direction are indicated accordingly
  

Solution:  Assuming that the average pedestrian speed = 1.2 m/s

                Pedestrian clear time along the major road = 12 / 1.2 = 10 seconds

                Peak green time = 10 + 7 = 17 seconds

                Pedestrian reaction time = 17 seconds

                Therefore, minimum green time for vehicle on minor street = 17 seconds

                Pedestrian clearance time for minor street = 6 / 1.2 = 5 seconds

                Pedestrian green time for vehicle on major street approach = 12 seconds

                Critical lane volume on major street = 660 / 2 = 330 vehicles/hour/lane

                Critical lane volume on minor street = 180 / 1 = 180 vehicles/hour/lane

                Green time on major street approach = (330/180)*17 = 31.16 seconds

                                                                                                        ~ 32 seconds

                Adding initial amber and clearance amber of 2 seconds each

                Minimum cycle length = (2 + 17 + 2) + (2 + 32 + 2) = 57 seconds           Adopting the next multiple of 5 we have the maximum cycle length as 60 seconds

Add 3 seconds (2 seconds for major street approach and 1 second for minor street approach = ratio of volume of traffic on major street to volume of traffic on minor street)

The results for the signal timing (in seconds) are tabulated below:

Signal                    Initial        Green        Clearance            Red                Cycle

timing                    Amber                        Amber                                         length    

Major street                2             34                2                        22                60        

Minor street                2             18                2                        38                60