Introduction
The first rudimentary versions of traffic signal control can be traced back to 1868 London, when manual semaphores were used to manage movement on the streets. The development of traffic signals in the United States of America was originally designed to assign right of way to different road users for the purpose of reducing the annual number of accidents observed. It is estimated that there are more than 300,000 traffic signals across the United States of America. They are considered to be an integral part of the transportation network; road chaos is observed when these traffic management systems fail. The development of complex transportation networks and vehicles combined with increased modern distractions for drivers has necessitated the advancement of traffic signals to offset challenges created by modernization and technological innovation (TEM, 2007).
A traffic signal is normally defined as a device that utilizes one or more lights (primarily linked to a given color) to warm transport route users of a given hazard or indicates changes in right of way. Traffic signals are normally referred to as stop-and-go lights, flashers, stoplights, and semaphores. The highest percentage of traffic signals is associated with traffic control devices. Most of these signals are install to manage a high influx of vehicles or pedestrians at a given joint; or in some cases to offset the occurrence of avoidable road crashes. It is considered that a good traffic signal that is properly developed, installed, utilized, and maintained in a crucial asset to the transport sector as a whole. It is viewed that an unjustified traffic signal that is poorly designed, installed, implemented, and maintained decreases the overall safety and efficiency associated with a given road intersection (TEM, 2007).
The decision to install a traffic signal at a given intersection should only be performed after a data-supported engineering study is conducted. The engineering study is supposed to provide data and results that warrant the installation of the traffic signal. If the study concludes that it is appropriate and justified for a traffic signal to be installed, the most recent and relevant design studies must be employed. The utilization of the latest design standards is supposed to ensure that the highest level of safety is observed. The installation of the traffic signal is done with adherence to special provisions and plans dispensed by the local road authority. After installation, the maintenance of the device has to be done to ensure its longevity and proper functionality. Traffic signals are considered to encompass all power-operated traffic control devices (i.e. mechanically, electronically, and manually operated devices); through which traffic is directed towards a given movement pattern or warned of conflicting movement. Traffic signals do not however include road signs since they are not power operated (Kittelson & Associates, 2008).
Therefore, traffic signals are employed in areas where conflict is bound when it comes to assignment of right-of-way; In addition, they are used where signs and markers are deemed ineffective towards the provision of safety, flexibility, and convenience on the road. Under the umbrella of engineering studies, there are several ways through which researchers are able to determine whether the installation of a traffic signal is justified and proper. Researchers are able to perform one or more of these assessments; pedestrian counts (for example, establishing the presence of a high number of children, elderly individuals, and handicapped persons in the area), volume studies (this involves turning movements, approach volumes, and peak-hour detailed counts), traffic gap studies, crash studies, intersection delay studies, and speed studies. The procedures to conducting effective traffic studies are prescribed in the “Institute of Transportation Engineers’ Manual of Traffic Engineering Studies” under which the process of data collection is also addressed to safeguard the reliability of the study findings (Kittelson & Associates, 2008).
Tables/Figures
Intersection traffic control signal is the most common type of traffic signal and it’s primarily function is to assign right-of-way to vehicular and/or pedestrian movement at a busy point where two or more streets or highways converge. It does this by ushering movement using three colors (red, yellow, and green). The green color allows drivers to go through and intersection while the motorists on adjoin roads are shown red (stop) and yellow (get ready). All in all, intersection traffic control signals allow pedestrians to safety cross busy roads/streets, prevents right-angle crashes, and promotes time optimization. There are several elements that constitute a great intersection traffic control signal. The first element is the ability of the signal to create indications that drivers are able to react and make movement decision. This is the most fundamental and basic facet of the traffic control system. The signal indication displays a message through the illumination of one or more colors in an alternating manner. The other elements of intersection traffic control signal are Poles, Mast Arms, Pedestals, Cabinet, Control Equipment, Detection, Source of Power, Service Equipment, Conduit, and Handholes (TEM, 2007).
Random Traffic Flow Model
Site Number: Site 1
Mean of the number of arrivals per 10 seconds: 2.033
Variance of the number of arrivals per 10 seconds: 3.269
Mean/Variance: 0.622
The above ratio expected for the Poisson distribution: 1
| Vehicle Count (per interval of 10 secs.) | ||||||||||
| Frequency | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| Observed | 25 | 14 | 17 | 16 | 8 | 7 | 1 | 2 | 0 | 0 |
| Theoretical | 0.00 | 0.00 | 0.00 | 0.00 | 5.15 | 11.49 | 0.05 | 0.31 | 0 | 0 |
Insert a comparative histogram or bar graph to show the observed and theoretical frequencies.
Site Number: Site 2
Mean of the number of arrivals per 10 seconds: 1.54
Variance of the number of arrivals per 10 seconds: 1.82
Mean/Variance: 0.85
The above ratio expected for the Poisson distribution: 1
| Vehicle Count (per interval of 10 secs.) | ||||||||||
| Frequency | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
| Observed | 26 | 20 | 23 | 14 | 4 | 3 | 0 | 0 | 0 | 0 |
| Theoretical | 0.00 | 0.00 | 0.00 | 0.03 | 17.58 | 9.07 | 0 | 0 | 0 | 0 |
Insert a comparative histogram or bar graph to show the observed and theoretical frequencies.
Traffic Signal Design
The critical movement around the intersection indicates that any vehicle entering the around about has three exit options; Therefore, there needs to be a traffic control signal for each of the four enters/exits at the intersection. The lights are supposed to switch from one leg of the roundabout to the next. The signal phase will change every 2 minutes to ensures that a significant number of cars move from one side to the next. The signal phases are red, yellow, and green. The three signal phases will change with regard to the Webster’s approach that optimizes the signal cycle time in a manner that minimizes the delay time to vehicles approaching the intersection.
Green light time allocation varies because there is a difference in number of vehicles arriving at the intersection from Dalton and Childs road. Since, the mean number of cars arriving at the intersection from Dalton is almost the number arriving from Childs road it is only logical that Dalton be given roughly 50% more green time compared Childs road to avoid issues of congestion. Therefore, if green time allocation for Childs road is 1 minute then Dalton road should be assigned 2 minutes. The final phase diagram can be illustrated as follows:
The actual map for the intersection is presented below:
Conclusions
In conclusion, we are able to see that an effective traffic signal for a busy intersection has to take into account the volume of vehicles coming from different direction in order to effectively assign right of way without causing vehicle congestion. The arrival of vehicles at the intersection of the two roads shows that a difference in green time allocation is necessary because of variation in the arrival of vehicles at the junction. The green time allocation for the Dalton road has to be greater because of a higher vehicle influx compared to Childs road. Overall, the maximum time allotted to the green light across any given phase should not exceed 2 minutes due to the heavy traffic influx at the intersection over any given one hour interval.
References
Kittelson & Associates, I. 2008. Traffic Signal Timing Manual. Washington D.C.: U.S. Department of Transportation Federal Highway Authority.
TEM, S. 2007. Chapter 9: Traffic Signals. In TEM, Traffic Engineering Manual . pp 3-44. Florida: Traffic Safety Team.
Random Traffic Flow Model
Site Number: Site 1
Mean of the number of arrivals per 10 seconds: 2.033
Variance of the number of arrivals per 10 seconds: 3.269
Mean/Variance: 0.622
The above ratio expected for the Poisson distribution: 1
