Adaptive Signal Control
|The City of Grapevine has one of the largest deployments of adaptive traffic signal control in the United States. Adaptive systems are intended to provide a more flexible means of adjusting to changing traffic conditions as compared to traditional signal timing and coordination.
When traditional signal coordination plans are developed, traffic counts are collected at key intersections over a period of a couple days, and timing plans are designed which control how much time each movement will get. In some cases, it is not practical to collect data at every intersection along a corridor, so assumptions are made about the volumes expected at the smaller intersections. The biggest limitation is that a brief snapshot of traffic conditions is used to create timing plans which will be run for years into the future. Traffic volumes can vary significantly over the course of a few minutes, and certainly will change over the course of years.
City staff adjusts these plans as time permits, and it is typically advisable for new data to be collected and for new timing plans to be developed and implemented every three years or so. This can become very time consuming and expensive, and even the most up-to-date plan does not allow the signal to adjust to unexpected changes in traffic, such as those due to special events, incidents, or construction.
The City’s adaptive system provides more flexibility because a computer decides how much time to allot to each movement on a minute-by-minute basis. The system utilizes video detection cameras which determine if traffic is present in each lane and how long it has been waiting. The computer then decides which movements to serve in order to keep the overall delay at the intersection to a minimum, while still trying to minimize the number of stops for vehicles travelling along the major roadway.