Safety Indicators for Heterogeneous Non Lane Based Traffic-A Case Study at Outer Ring Road-Delhi

Road safety is an important aspect which requires immediate attention in transportation engineering. Use of safety indicators/surrogate safety measures for traffic safety in transportation engineering has been increasing day to day. Safety analysis can be done in two ways-reactive point of view and preventive point of view. Researchers are more interested in traffic safety analysis with preventive point of view than reactive point of view. Reactive approach needs significant number of detailed crash data analysis, crash frequency, etc., which are quite expensive and also errors can occur while collecting crash data like understanding of crash failure mechanism, manual error in recording crash data, etc. In developing countries like India, it is quite difficult and expensive to get large and reliable crash data base due to lack of funds and technology. One of the objectives of safety analysis in preventive point of view is to derive safety indicators/surrogate safety measures which help to understand and analyze the crash phenomena. Some surrogate safety measures which are frequently used are time to collision (TTC), deceleration rate, post encroachment time (PET), maximum speed, speed differential, merge area encroachments (freeway on ramp merging), variable driver reaction time, etc.

In the past, various works on identification of safety indicators has been carried out for homogeneous and lane discipline traffic in developed countries. However, such studies for heterogeneous and no lane disciplined traffic which exists in India is missing. This motivates to identify the suitable safety indicator for Indian Traffic. Three parameters like longitudinal headway, lateral headway and percentage overlap will be evaluated as their use as safety indicator for Indian traffic. Due to heterogeneity and absence of lane discipline vehicle interact with other vehicles in its neighborhood not only in longitudinal direction but also in lateral direction. Using combination of safety indicators conflict event are evaluated. A relation between traffic flow (volume) and conflicts is proposed that is, when traffic flow increases conflicts also increase and vice versa. Data collected from real world traffic stream is evaluated in order to determine the conflicts.