Webster Method of Designing Traffic - Report Example

Introduction The steps for doing the Webster method of designing traffic 1. Decide on a phasing plan. 2. Calculate the length of the intergreen period for each phase of your cycle. 3. Calculate the minimum green time for each phase based on the pedestrian crossing time. 4. Calculate or measure the saturation flow rate for each approach or lane. 5. Calculate the design flow rate for each approach or lane using the peak hour volume and peak hour factor. 6. Find the critical movements or lanes, and calculate the critical flow ratios. 7. Calculate the optimum cycle length. 8. Allocate the available green time using the critical flow ratios from step six. 9. Calculate the capacity of the intersection approaches or lanes. Check the capacities/design flow rates and green intervals/minimum green intervals. Adjust your cycle timing scheme if necessary. The year 1950 saw Webster doing a series of experiments on pretimed isolated intersection operations and there has been two traffic signal timing strategies that has been found with one including the signal phase splits and the other being minimum delay cycle length model. Webster’s method Based on an estimate of the average delay per vehicle at a signalized intersection,this method determines cycle times and green-splits of pre-timed signals that minimize delay. The present data The appropriate lanes East Bound 200 including 15 commercial vehicles from the northern side. 15 commercial vehicles from the Southern side 650 including 50 commercial vehicles from the west bound. Total number of vehicles is 865 West Bound 374 including 40 commercial vehicles from the eastern side. 70 including 8commercial vehicles from the southern side 30 including 6 commercial vehicles from the northern side. Total number of vehicles is 434 North Bound 1500 including 210 commercial vehicles from the southern side. 30 including 8commercial vehicles from the western side 21 including 9 commercial vehicles from the eastern side. Total number of vehicles is 1551 South Bound 1400 including 200 commercial vehicles from the northern side. 20 including 3 commercial vehicles from the eastern side 0 vehicles from the western side. Total number of vehicles is 1420 Intersection The term intersection would mean that two or more lanes in traffic would be joining at cross. There would be many modes of travel like the pedestrian, bicycle, motor vehicle, car, transit and other forms of travel. There should be areas for adjacent walk. Intersection would mean that there would be a focus of activity like the land near the intersection, there would be an assessment of conflicting movements like pedestrian crossings and motor vehicle and bicycle turning and crossing movements that would be concentrated at intersections. There should be traffic control mechanism like the yield signs, stop signs and traffic signals. The traffic control at intersections would be limiting the capacity of intersecting roadways and that could be defined at the number of users that could be accommodated at given time period. The people who are walking could be called pedestrians and there has to be amount of right way that has to be provided using the side walk and cross walk width and that has been the accuracy of slopes and cross slopes on curb that would be cutting ramps and walkways. There has to be audible and there has to be presentation for walking for people with limited sights and there has to be a distance that has to be fixed for crossing and there has to be understanding of terms like volume of conflicting traffic and there has to be speed and visibility of approaching traffic. There has to be understanding of conflicting traffic. The bicycles would be having a different intersection level and there should be understanding of how pavement is shared and that has been used by the bicycles and there has to be proper understanding of turning the bicycles and there has to be traffic control for bicycles and traffic control for bicycles and there has to be differential in speed between the motor vehicle and Traffic control for biclycles.There has to be visibility for bicyclist and that has to be understood more in detail. There has to be understanding of motor vehicles and there has to be understanding of traffic control and vehicular capacity of intersection and there has to be number of lanes and there has to be ability for turning movements and there has to be visibility for approaching and crossing pedestrians and bicycles and there has to be understanding of visibility also. There has to be understanding of retail and commercial institutions that has to be there. The intersection design could be said as follows There would be intersection that would be called as simple intersection and that would be using the number of lanes using the intersection and there would be understanding of major and minor streets. (Sasan Dashtinezhad, Tamer Nadeem, Bogdan Dorohonceanu, Cristian Borcea, Porlin Kang and Liviu Iftode )There has to be understanding of simple intersections and there has to be understanding of auxiliary turning that has to be achieving the desired level. There would be minimum crossing distance for pedestrians and that has been in common in low-volume locations. There would be flared intersections that would be expanding the cross section of the street and there would be accommodation of left lane and left turning would be done to increase the capacity for high volume locations. There has to be safety for higher speed streets. There has usage of right-turn lanes, that would be frequently used than left-turn lanes, and that would be in response to large volumes of right turns. Intersection approaches would be flared to make the vehicle turning movement That would be approaching or going away from the intersection. These flaring would be beneficial for bicycle and there has been motor vehicular and there would be possibility for higher speed movements and there has to be adding flare that would be intersection increases that would be affecting the pedestrian crossing . There would be need for Transit stops that would be needed at intersections and there has to be location near intersections that would be beneficial when the transit routes would be crossing and there would be minimal walking distance that would be needed for passengers that would be boarding the bus. There could be bus stop that would be requiring the 50 to 70 feet curb space and there should be provision for buses to stop in moving traffic and that would be requiring at least 5 to 6 seconds per person. These could be said as diagram that would be said here in exhibit one. Auxiliary lanes: These are lanes that are added at the intersection. These are added to adjust to the left turning of vehicles. They are added less for the right turning of vehicles. There would be adding of lanes through an intersection.( Newell, G. F. ,2000). The channelizing islands would be having areas that would be marked for pedestrian refuge. Turning road ways would be done to accommodate people turning right side and that would be meaning that it would be used when the right-turn volumes are very high, and there could be cases of intersection that would be creating a very large pavement area.There has to be angle of pavement and that has to be done and that has to be done for different segments like shown below There has to be understanding of intersections and these could be termed as follows This intersection would be having this simple intersection or flared intersection. Intersection approach should be flared slightly and there has to be enough for approach road if any.That would be benfitting the cycle movement and other types of movement. The case study would be presenting intersection as close to right angles as practical. Skewed intersections can reduce visibility of approaching motor vehicles and bicycles, require higher degrees of traffic control, require more pavement to facilitate turning vehicles, and require greater crossing distances for pedestrians. Webster method solutions 1.The method of phasing that would be used would be the flared method.There has to be a digram representation Intergreen Time The time would be having a phase in which there would be yellow and red indication. There would be stopping distance and intersection clearance time. There would be pedestrian crossing time provided there are no signals. In this case there would be no signals.( Bell, M. G. H. and D. Brookes ,2003). The yellow signal would be considered as a warning by drivers and intergreen interval should be there long enough for the divers to apply brakes as the signal would be turning red.( Dunne, M. C. ,2007). The intergreen phase should be allowing the vehicles to pass the intersection smoothly. The zone would be called as dilemma zone and intergreen time is less would mean that only those vehicles that are close to the intersection would be able to pass through.That would also mean that vehicles that are at distant would be having adequate time to react and stop.This could be shown as a graphic model. ( Luh, J. Z. and Chung Yee Lee ,2001). The first thing to do is to reduce the dilemma zone.That would be helping any vehicle to stop safely or proceed through the intersection during the intergreen period. This has to be done using or making sure that the vehicle closer to the intersection would be having minimum braking distance and that should be done without accelerating and speeding. The minimum safe stopping distance would be calculated and that would mean Minimum Safe Stopping Distance: SD = 1.47*Vo*tr + (1.47*Vo)2/(30*[f ± G]) Where: SD = Min. safe stopping dist. (ft) Vo = Initial velocity (mph) tr = Perception/Reaction time (sec) f = Coefficient of friction G = Grade, as a percentage The intersection phase that has been calculated has been as follows Intersection size has been identified as medium in which the intergreen time default has been fixed as 5 seconds per phase. The type of control in small would be 4 seconds while in large would be 6 seconds per phase. The design process that would be undertaking would be 5 seconds per phase. There would be three phases that would be used and that would mean that it would be twp phase, three phases and four phases. In two phase control the feasible time cycle control would be 40 to 80 seconds and in three phase control the feasible time control would be 50 to 100 seconds and four phase would be having a intergreen time of 80-130 seconds. The control that would be taken in this decision would be the three phasing. Cycle times lower than the recommended values would be having difficulties for pedestrian to make the crossing of streets. There would be cycle time that has to be more than 130 seconds and that has to be avoided and that would mean that the overall capacity should be avoided. Intersection Clearance Time: T = (SD + L + W)/(1.47*Vo) Where: T = Intersection clearance time (sec) Vo = Initial velocity (mph) L = Length of the vehicle (ft) SD = Min. safe stopping dist. (ft) W = Width of the intersection (ft) Question threePedestrian Crossing Time: PCT = W/V Where: PCT = Pedestrian crossing time (sec) W = Width of the intersection (feet) V = Velocity of the pedestrian (usually 4 ft/sec) =3/4 feet/sec=.75 The minimum green time for each phase               Provided Intergreen time (sec): 5                 Initial velocity (mph): 45       Perception/reaction time (sec): 1.4       Coefficient of friction: 0.9       Grade: 0.01                 Intersection width (ft): 50       Length of vehicle (ft): 18             The formulaes that has been used and the values that has been used Approach speed Minimum time to stop Phase one Phase two Phase three 20 2 5.6 5.7 6.4 30 2.5 4.5 5.0 5.5 40 3 4.5 4.9 5.2 50 3.4 4.7 5.0 5.2 60 3.9 4.9 5.1 5.4 Calculate or measure the saturation flow rate for each approach or lane Saturation flow rate Saturation flow should be considered as a measure of junction operation. That would indicate the potential capacity of a junction and that would be operating under ideal conditions. Ideal conditions should be having an width of 3,6 meter lane width;There should be no heavy vehicles and there should be no flat gradient and there should be no parking at bus stops at the intersection and there should be uniform movement type and that means there should be straight movement or having only turning movement.There would be no pedestrians and cyclists at the time of study and that has to be identified. (Little, J. D. C. ,2001). Approach Mean Sample size Standard deviation minimum maximum Eastern corridor 1800 100 133 1839 2254 Western corridor 2080 64 133 1565 1946 Southern corridor 1710 35 151 1625 2071 Northern corridor 1778 45 204 1879 2471 The saturation rate that has been through lanes and conditions Intersection Number of through lanes gradient Speed limit Movement Saturation flow rate East-west 2 0 60 through 2026 East-south 1 0 60 right 1711 West-south 1 0 60 Right 1820 North-south 1 0 60 through 1844 The key factors that has to be understood would be that If speed limit is increased from 60,then the saturation flow would be increased in each sections. At present the speed limit has been set at 60 km per second. That could be termed as an assumption. The through lanes would be increased and that would be increasing the number of saturation flow. The lanes could be increased from one to two. In the case of East to West, there has been an increase of saturation flow. There has been an increase in the gradient flow and that would be decreasing the saturation flow and that means a vice versa would be happening. The saturation flow that has been on single right turn lanes would be greater than that of a single through lane. Calculate the design flow rate for each approach or lane using the peak hour volume and peak hour factor Based on Webster’s model the general equation to replicate the time involved for delay would be That would mean x = Traffic volume on entering link, in vehicle (passenger car equivalent) per hour.  = Exiting rate of traffic volume, in vehicle (passenger car equivalent) per one meter width per hour. r = Red time of the traffic light, in minutes. c = Cycle length of the traffic light, in minutes. d = Average delay at intersection, in minutes. w = Width of the link, in meter. In order to avoid possible occurrence of error, max{[1-x/(*w)] and 0.01} was used instead of [1-x/(*w)]. Scenario Description r2 nointersection delay functions 0.69 Using just unsignalized intersection delay functions 0.72 Using just signalized intersection delay functions 0.75 Using both signalized and unsignalized delay functions 0.77 (Kimber, R. M. and E. M. Hollis ,2008). In this equation, t(x) and t0 are travel time on link and the free flow travel time in minutes, l is the length of the link and c is the capacity of each link per meter of the street width which varies depending on the functional class of street.( Luh, J. Z. and Chung Yee Lee ,2001). Find the critical movements or lanes, and calculate the critical flow ratios Webster method Webster’s method CO = optimum cycle length L = sum of intergreen periods V/s = ratio of design flow rate with saturation flow rate The peak hour volume would be using the approach,lane,lane group in question during the hour of the day.The rush hour would be considered as the peak hour. Peak Hour Factor: PHF = Peak hour volume/(4*Peak fifteen minute volume). There would be finding of critical path like CO is the optimum cycle length. L is the sum of lost times for all the phases (yellow and all-red times). n is the number of critical lane groups. A critical lane group is a group of movements that can access the intersection concurrently. vi / si is the maximum flow ratio for the critical lane group i. 1 / Xc is the desired degree of intersection utilization. The figures that has been got has been -8.04,-21,3 and 21. Calculate the optimum cycle length C0=1.5+L/1-Y where c0 = the optimal minimum delay cycle length, sec; L = total lost time within the cycle, sec; and Y = the sum of critical phase flow ratios (2). optimum cycle length would be related to the minimum total delay of the intersection. That has to be done using appropriate cycle length and green splits. There has to be a given cycle length, the effective green phases would be selected in proportion to the critical flow ratio of the phases. There has to be obtaining of optimal cycle length that has to be taken to derivative of the expression for total delay of the intersection with respect to cycle length and set equal to zero. Growth factor Total volumes Intersection delay Webster secondc0 at 12 second 1/1-y 1 1080 17.1 34 1.47 1.2 1296 19.9 38 1.67 1.5 1620 24.7 46 2.00 1.9 2052 32.5 61 2.63 2 2160 35.9 64 2.78 Growth factor Total volumes Intersection delay Webster secondc0 at 14 second 1/1-y 1 1080 19.1 38 1.47 1.2 1296 21.9 43 1.67 1.5 1620 26.4 52 2.00 1.9 2052 33.1 62 2.38 2 2160 35.8 68 2.63 Allocate the available green time using the critical flow ratios The green time that has to be allocated using the critical flow ratios would be for east to west more. Check the capacities/design flow rates and green intervals/minimum green intervals. Adjust your cycle timing scheme if necessary. Calculate the capacity of the intersection approaches or lanes. There would be more capacity for the east west corridor. Reference Sasan Dashtinezhad, Tamer Nadeem, Bogdan Dorohonceanu, Cristian Borcea, Porlin Kang and Liviu Iftode – “TrafficView: a driver assistant device for traffic monitoring based on car-to-car communication,” Proceedings of IEEE Semiannual Vehicular Technology Conference, Milan, May 17-19, 2004. Bell, M. G. H. and D. Brookes (2003). Discrete Time- Adaptive Traffic Signal Control. Transportation Research, Vol. 1C, No. 1, pp. 43-55. Dunne, M. C. (2007). Traffic Delay at a Signalized Intersection with Binomial Arrivals. Transportation Science, 1, pp. 24-31. Luh, J. Z. and Chung Yee Lee (2001). Stop Probability and Delay Estimations at Low Volumes for Semi-Actuated Traffic Signals. Transportation Science, 25(1), pp. 65-82. Kimber, R. M. and E. M. Hollis (2008). Peak Period Traffic Delay at Road Junctions and Other Bottlenecks. Traffic Engineering and Control, Vol. 19, No. 10, pp. 442-446. Little, J. D. C. (2001). Approximate Expected Delays for Several Maneuvers by Driver in a Poisson Traffic. Operations Research, 9, pp. 39-52. Newell, G. F. (2000). Stochastic Delays on Signalized Arterial Highways. Transportation and Traffic Theory, Elsevier Science Publishing Co.,Inc., M. Koshi, Ed., pp. 589-598. Read More

(Sasan Dashtinezhad, Tamer Nadeem, Bogdan Dorohonceanu, Cristian Borcea, Porlin Kang and Liviu Iftode )There has to be understanding of simple intersections and there has to be understanding of auxiliary turning that has to be achieving the desired level. There would be minimum crossing distance for pedestrians and that has been in common in low-volume locations. There would be flared intersections that would be expanding the cross section of the street and there would be accommodation of left lane and left turning would be done to increase the capacity for high volume locations.

There has to be safety for higher speed streets. There has usage of right-turn lanes, that would be frequently used than left-turn lanes, and that would be in response to large volumes of right turns. Intersection approaches would be flared to make the vehicle turning movement That would be approaching or going away from the intersection. These flaring would be beneficial for bicycle and there has been motor vehicular and there would be possibility for higher speed movements and there has to be adding flare that would be intersection increases that would be affecting the pedestrian crossing .

There would be need for Transit stops that would be needed at intersections and there has to be location near intersections that would be beneficial when the transit routes would be crossing and there would be minimal walking distance that would be needed for passengers that would be boarding the bus. There could be bus stop that would be requiring the 50 to 70 feet curb space and there should be provision for buses to stop in moving traffic and that would be requiring at least 5 to 6 seconds per person.

These could be said as diagram that would be said here in exhibit one. Auxiliary lanes: These are lanes that are added at the intersection. These are added to adjust to the left turning of vehicles. They are added less for the right turning of vehicles. There would be adding of lanes through an intersection.( Newell, G. F. ,2000). The channelizing islands would be having areas that would be marked for pedestrian refuge. Turning road ways would be done to accommodate people turning right side and that would be meaning that it would be used when the right-turn volumes are very high, and there could be cases of intersection that would be creating a very large pavement area.

There has to be angle of pavement and that has to be done and that has to be done for different segments like shown below There has to be understanding of intersections and these could be termed as follows This intersection would be having this simple intersection or flared intersection. Intersection approach should be flared slightly and there has to be enough for approach road if any.That would be benfitting the cycle movement and other types of movement. The case study would be presenting intersection as close to right angles as practical.

Skewed intersections can reduce visibility of approaching motor vehicles and bicycles, require higher degrees of traffic control, require more pavement to facilitate turning vehicles, and require greater crossing distances for pedestrians. Webster method solutions 1.The method of phasing that would be used would be the flared method.There has to be a digram representation Intergreen Time The time would be having a phase in which there would be yellow and red indication. There would be stopping distance and intersection clearance time.

There would be pedestrian crossing time provided there are no signals. In this case there would be no signals.( Bell, M. G. H. and D. Brookes ,2003). The yellow signal would be considered as a warning by drivers and intergreen interval should be there long enough for the divers to apply brakes as the signal would be turning red.( Dunne, M. C. ,2007). The intergreen phase should be allowing the vehicles to pass the intersection smoothly. The zone would be called as dilemma zone and intergreen time is less would mean that only those vehicles that are close to the intersection would be able to pass through.

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