Traffic Q&A: Ramp meters turned on when algorithms say so

Q: How come the on-ramp from South Union Avenue to westbound state Route 16 is never metered during the evening commute? It seems like 15 cars are trying to merge at once and sometimes cause traffic on 16 to come to a complete and sudden stop.

Evan D., University Place

A: Because the algorithms say so, Evan.

Let’s go to Doug Adamson of the Washington state Department of Transportation for elaboration.

“WSDOT uses traffic data and mathematical algorithms to determine when ramp meters will be effective in helping delay the onset of congestion or reduce the time congestion is present,” Adamson told The News Tribune. “The ramp meter on the South Union Avenue on-ramp to westbound state Route 16 currently is inactive because traffic conditions at this time don’t require operation of that particular meter. If conditions change, we will activate the meter as needed.”

So how will engineers know when to consult the algorithms, a driver might wonder.

Here’s Adamson again:

“Roadway sensors send information to a computer system that quickly crunches data. While the technology automatically activates ramp meters based on freeway conditions, the system can be manually overridden by WSDOT staff based on a number of factors, including collisions or other roadway incidents.”

One might wonder why DOT installed a meter there at all.

Adamson had an answer for that.

“Permanent ramp meters are usually installed during large construction projects and are activated along an entire corridor when WSDOT traffic engineers determine they will help alleviate congestion,” he said. “The South Union Avenue ramp meter was built as part of ongoing effort to bring HOV lanes into Pierce County.

“Ramp meters are a proven approach to reduce freeway congestion and collisions.”

This story was originally published January 30, 2016 at 9:28 AM with the headline "Traffic Q&A: Ramp meters turned on when algorithms say so."