The Collision Points on Unsignalised Intersectyions and the Effect of Upstream Signals
S P Çaliskanelli, S Tanyel, M Özuysal, Dokuz Eylul University, TR
Evaluation of the effects of distance between the signalization and unsignalized intersection on the statistical distribution of gaps in major traffic stream and the usefulness of these gaps to the minor stream drivers.
The road parts which are used by the traffic that comes from the different sides are called intersections. The crossing and turning maneuvers that occur at intersections create traffic crash opportunities for vehicle-vehicle, vehicle-pedestrian, and vehicle-bicycle conflicts.
Because of these conflicts, intersections are likely points for concentrations of traffic crashes. Long delays occur at these parts of the roads.
The volume and the location are very important on control type of the intersections. To minimize crash frequency and severity, appropriate intersection traffic control type should be chosen. Good geometric design combined with good traffic control can result in an efficient and safe intersection. As population and development increases, traffic volume and the number of crashes grow. There is an increasing demand for signalization at urban and suburban intersections even in rural areas. However, experience shows that intersection crash rates frequently increase with signal installation, although the crashes may be less severe( NCHRP Report 500,Volume 5). Signalization usually leads to a shift in crash types, with fewer angle and turning collisions and more rear-end collisions.
Some collisions at unsignalized intersections occur because drivers have difficulty in judging gap sizes before deciding whether to initiate a roadway entry or a turning maneuver. Drivers stopped to wait for the oncoming traffic stream often choose to proceed when oncoming vehicles are close, thus increasing the probability for a collision. Some precautions could be taken to improve safety at unsignalized intersections. For this purpose the availability of gaps in traffic stream could be arranged and automated systems can be used to assist drivers in judging gap sizes in traffic stream for entering the major road from a controlled approach. The signal timing can be modified to create longer gaps. Some crashes can be minimized if longer gaps can be made available.
Unsignalized intersections are often modeled with an assumption of random vehicle arrivals. However vehicle arrivals are not random where nearby upstream signalized intersections cause platoons. The queues that form at each signalized intersection during the red phases will disperse as they travel downstream away from the signalized intersection. A platoon departs from a signalized intersection during the green phase at a particular flow rate but the platoon is dispersed by the time it passes a point downstream.
The presence of upstream signal effect is commonly an encountered condition that is not adequately accounted for capacity calculations and safety evaluation. The purpose of this study is to evaluate the effects of distance between the signalization and unsignalized intersection on the statistical distribution of gaps in major traffic stream and the usefulness of these gaps to the minor stream drivers. At the capacity calculations HCM 2000 procedure and a simulation program is used. The use of Cowan m3 distribution is also investigated for the main road vehicles. For the headways especially bigger than the critical gap values Cowan m3 distribution fits the observed values. To observe the efficiency some signalized and unsignalized intersection specimens in Izmir-Turkiye are taken into consideration.
Association for European Transport