Ada County Highway District

ACHD's Road Wizard Sunday, January 14, 2017 ACHD's Road Wizard

Afternoon traffic delays through the signal cluster of Cole Road at Interstate 84 explained; reader still happy about the new "dog bone" roundabout at Hill Road and 36th Street.

The Road Wizard Replies

Dear Road Wizard: I travel on Cole Road at least once a week. When I'm heading home, the lights northbound from Century Way to the westbound Interstate 84 on-ramp are ridiculously off-kilter. I sat at one of the lights in front of Cracker Barrel for two cycles. I surely can't be the only person who has complained about this. I'm traveling in the mid-afternoon when this occurs. Is there something that can be done about the timing of these lights?


Road Wizard:

A special "get off-ramp traffic off the off-ramp" signal timing mode is frequently put into effect this time of year, which can disrupt traffic flow on this roughly quarter-mile section of Cole with its cluster of signalized intersections.

The off-ramp from eastbound Interstate 84 onto Cole tends to fill up during the holidays with people traveling to places like Costco. ACHD traffic engineers will then give the off-ramp extra green time as needed. This mostly occurs between noon and 2:30 p.m. from before Thanksgiving through mid-January.

This results in less time for other directions at the off-ramp/Cole/Spectrum Street intersection. For example, northbound Cole's green may be reduced by five seconds, and some drivers won't make the light. If this goes on for many signal cycles, the congestion starts stretching to the signal on Century Way. But waiting on Cole is safer than clogging the off-ramp, forcing drivers to stop and wait on the interstate with traffic zooming by at 65 mph.

There are other contributors to delays on this part of Cole, which includes the big Overland Road intersection. There has been a lot of development in the area, in addition to an existing pattern of traffic surges in the afternoons. Many of these motorists are jockeying for position to get to the westbound Interstate 84/eastbound Interstate 184 Connector on-ramp.

The latest effort to improve the situation involves installing new traffic signal controllers and detection systems, along with sophisticated computer software. The technology is being tested with positive results on Chinden Boulevard between Locust Grove Road and Idaho 16. The upgrade is planned for the Cole and Overland area in a year or so.

This new technology should help traffic engineers better pinpoint the most efficient ways of programming the traffic signals on Cole. Right now, the signal timing is based primarily on the counting of vehicles during peak hours on a typical day in the past. Green light times are then set to serve the average number of drivers expected to arrive at signals.

Manual adjustments can already be made along the way, but the new technology goes beyond car-counting and the observation of traffic through the human eye. The system constantly tallies vehicles moving through intersections in real time, collecting the data from many signals at once. Based on that level of detail, signals can be adjusted more frequently to account for variations in traffic volumes.

Dear Road Wizard: Every time I use the "dog bone" roundabout at 36th Street and Hill Road, I appreciate what an improvement it is over the old intersection. Kudos to those who designed it. They thought of every detail to make it work smoothly. Thanks for the landscaping, too.


Road Wizard:

Your comments are appreciated. Years of planning and much public input went into the project, and it shows.


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