Estimating dilemma zone hazard function at high speed isolated intersection

Anuj Sharma et al. — Fri, 10 Dec 2010 08:18:55 PST

Abstract The traditional surrogate measures of safety (like number of vehicles in dilemma zone) fail to quantify the risk of crash. Traffic conflict has been proposed as an improved surrogate measure of safety for operations at isolated intersections to quantify the risk. This paper develops a dilemma zone hazard function estimating procedure to obtain the probability of traffic conflict occurring. This approach is an extension of the current approach of dilemma zone boundaries to determine the risk of traffic conflict for an individual vehicle in the case of a dilemma zone incursion. Field data collected from the intersection of SR37 and SR32 at Noblesville, Indiana is used to generate a binary choice model that best explains the underlying criteria for a driver’s decision at the onset of yellow. The probability of making an erroneous decision is used as the probability of traffic conflict (dilemma hazard function). An economic framework was developed to implement the dynamic of dilemma hazard function using existing controllers. Although the data are specific to one intersection, the procedures are readily transferable. This paper also demonstrates the potential of sensor providing richer data than an inductive loop detector can be used to further enhance the safety at signal operations.

Effect of Phase Countdown Timers on Queue Discharge Characteristics Under Heterogeneous Traffic Conditions

Anuj Sharma — Thu, 02 Dec 2010 15:03:10 PST

Analysis of queue discharge characteristics at signalized intersections is a primary component of traffic signal analysis and design. On the basis of previous studies, mainly conducted in homogeneous traffic conditions, the discharge headway is assumed to be high at the start of green for the first few vehicles, mainly because of start-up lost times, and is also assumed to reach the minimum value by the fourth or fifth vehicle in the queue. The minimum headway is expected to continue until the end of the queue. However, this may not be the case under heterogeneous traffic conditions, such as those in India, which has the additional problem of lacking lane discipline. Most of the signals in India include a countdown timer that indicates the time left for the signal phase, which is also expected to affect queue discharge characteristics. This paper presents insights gained on queue discharge characteristics at signalized intersections under heterogeneous traffic conditions and on the effect of a countdown timer on the headway distribution. The analysis was carried out using data collected from two intersections, one with a timer and one without, in Chennai, India, through the use of a videographic technique. The data collected are classified into three discharge regimes: start-queue, mid-queue, and end-queue. Linear regression models are used to assess the impact of vehicle types on queue discharge characteristics. The results indicate that the accepted headway distribution is followed when there is no timer. However, with the presence of a timer, there is a clear change in the trend for reduced start-up lost time and end lost time.

Anuj Sharma Publications

Estimating dilemma zone hazard function at high speed isolated intersection

Effect of Phase Countdown Timers on Queue Discharge Characteristics Under Heterogeneous Traffic Conditions