New Detection System for Rural Signalized Intersections

Project Summary Report 0-4022-S – 1 – Traffi c engineers are often faced with operational and safety challenges at rural, high-speed signalized intersections. Vehicleactuated control, combined with multiple advance detectors, is often used to improve operations and safety. However, this type of detection and control has not always eliminated rear-end or right-angle crashes. Crashes sometimes continue to occur at high-speed intersections, and delays to traffi c movements can be unnecessarily long. The existing multiple advance detector system holds the traffi c signal in green until a suitably large gap occurs in the traffi c stream. Through this action, the system ends the phase safely because the approach is empty. However, this gap occurs infrequently on high-volume approaches and often causes the corresponding signal phase to extend to its maximum limit (i.e., max-out). When the phase reaches this limit, it ends without regard to the number of vehicles on the approach and increases the potential for a rear-end crash. If the maximum green setting is large, then the resulting delays may also be large. The high-speed nature of most rural intersections heightens concerns about phase termination by max-out because crash severity increases signifi cantly with speed. Other problems exist with the multiple advance detector system. referred to as the “dilemma zone” or the “indecision zone” because it represents that portion of the intersection approach within which drivers exhibit distinct differences in their desire (or ability) to stop when presented the yellow indication. On a typical approach, the indecision zone starts at about 5.5 seconds travel time from the intersection. At the same time that the new system is monitoring approaching vehicles, it is also searching for a time in the near future when the total number of drivers in their respective indecision zones is at a minimum. This future time is defi ned as the “best time to end the phase.” Other factors that are also considered when deciding the best time to end the phase include: (1) whether the vehicle is a large truck and (2) the delay to drivers waiting on the minor road. At the start of each signal phase, the new system begins searching for the best time to end the phase. However, if it is unsuccessful after 30 to 40 seconds and if there are several drivers waiting on the minor road, the system relaxes the search criterion and ends the phase when there is a maximum of one car (no trucks) in its indecision zone. In short, the most unique feature of the new system is its ability to “dynamically” identify the indecision zone for each They include: • Its operation is not sensitive to the type of vehicle on the approach (i.e., car or truck).