Ada County Highway District

News and Press Releases Tuesday, April 7, 2020

Traffic volumes down, ACHD adjusts signal timing

As a result of Governor Little's stay-home orders, traffic volumes in Ada County are down about 40 percent over the course of each day. To accommodate these newly freed-up roads and intersections, the Ada County Highway District has adjusted traffic signal timing at various locations to improve traffic flow.

Photograph of traffic signalTypically, an intersection might have four timing plans: an A.M. plan, a midday plan, a P.M. plan and an off-peak plan. The A.M. and P.M. plans usually have longer cycle lengths to favor the dominant movements. During the morning commute, inbound traffic is favored as thousands of vehicles pour into downtown Boise, while in the evening outbound traffic is favored as those motorists make their way back home. This can cause increased delays for traffic going the other way.

Looking at CCTV cameras and monitoring traffic counts, ACHD engineers found many cycle lengths were too long with the recent drop in traffic. With the newly implemented timing plans, many different corridors are operating on the midday plan or an off-peak plan.

Eagle Road, for example, is on the midday plan during the evening now. This is typically more balanced with shorter cycle lengths. So far, this appears to be working. Traffic is still flowing on Eagle Road and the side streets don't have to wait as long for a green light.

Some corridors like Parkcenter Boulevard or Ustick Road are on off-peak plans. Off-peak plans are when the signals are "free operation." This means traffic signals use the vehicle detection to operate the cycle on demand, so it cycles frequently.

Based on initial observations after the adjustments, traffic is still moving well. ACHD will continue to monitor things to see if any adjustments are needed.

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