Monday, August 15, 2016

Turning on a ramp meter isn’t as easy as just flipping a switch

By Justin Fujioka

Can the flutter of a butterfly's wings really cause a tornado halfway around the world? Whether or not you believe in the butterfly effect, it's not something we want to risk when turning on a new ramp meter.

Traffic signals on Coal Creek Parkway will be synced to work
in conjunction with the new ramp meters to I-405.
And that's why it has taken us several months to flip the switch on two southbound I-405 ramp meters in Bellevue and Tukwila. After a combination of funding delays, extensive data collection and signal modifications on surface streets, we've got the green light for ramp meters at Interurban Avenue South/SR 181 and at Coal Creek Parkway to be turned on in mid-August.

Ramp meters are used across the country to create an even pace for vehicles entering the highway to improve safety and traffic flow along busy corridors – in this case, southbound I-405. But installing a ramp meter without careful and thoughtful research, consideration and collaboration with local governments could create a negative butterfly effect in the way of increased congestion on other roadways.

Interurban Avenue South/SR 181 on-ramp in Tukwila
We turned off the original ramp meter on the Interurban Avenue South/SR 181 on-ramp to southbound I-405 for a City of Tukwila construction project in 2011, when there was an HOV bypass lane on the ramp and a metered general purpose lane.

A new “No Right Turn on Red” signal will be installed
to assist traffic flow near the I-405 ramp.
At the time, we'd received several comments about the HOV lane being underutilized and traffic in the general purpose lane backing up onto Interurban. The City of Tukwila was also preparing to close the intersection of Southcenter Parkway and Klickitat Drive, where many people leaving the mall access southbound I-5. The planned detour route was the Interurban on-ramp to southbound I-405. A combination of the two lead us to a collaborative decision with the city to turn off the ramp meter and convert the HOV lane to a second general purpose lane for better utilization of the ramp.

The plan at the time was to eventually put up a new ramp meter with two general purpose lanes once the Southcenter/Klickitat intersection reopened. But due to a lack of funding, we weren't able to install a new ramp meter until this past spring. We'll flip the switch on this ramp meter on Monday, Aug. 15.

Coal Creek Parkway on-ramp in Bellevue
The Coal Creek Parkway ramp meter to southbound I-405 was installed in the spring and summer of 2015. Prior to that, King County Metro Transit moved a bus stop from the on-ramp to a nearby park-and-ride, leaving the existing bus pull-out available for general purpose traffic. We took the opportunity to use this space to create a second general purpose lane when we turn on the ramp meter on Wednesday, Aug. 17.

These new I-405 ramp meters will help maintain traffic flow on the interstate.

That second lane will provide more space for vehicles entering southbound I-405 in an area that gets congested during peak commute times. But what if both lanes get backed up? That's what we've been working with the City of Bellevue on over the past year by collecting data at a couple of intersections just upstream of the ramp. The city has been using this research to sync signal timing along Coal Creek Parkway with the new ramp meter.

These new ramp meters become active on Monday, Aug. 15.
While it won't look much different, the city will make some noticeable changes at the southbound I-405 ramps/Coal Creek Parkway intersection. Traffic coming from downtown Bellevue on 118th Avenue Southeast making a right turn onto the ramp will now be signal controlled. A "No Right Turn on Red" sign will be lit up whenever the ramp is being metered and dark during all other times. Previously, the right-turn lane was free-flowing 24/7.

Also, traffic coming from Factoria on Coal Creek Parkway making a left turn onto the ramp will get signal priority at the intersection to utilize the extra space on the ramp and help avoid congestion on Coal Creek.

For the first few weeks of operation, we'll be watching both ramp meters very carefully to see if modifications are needed. We expect drivers to take some time adjusting to the new traffic patterns as well. Both ramp meters will only activate when traffic on southbound I-405 dips below the posted speed limit. Signal timing is no simple task and it takes engineers much time and finesse making sure everything is just right. For many, understanding the science behind it may be just as hard as understanding the butterfly effect.

Two new Pierce County ramp meters activated
In addition to ramp meters being activated in Bellevue and Tukwila, ramp meters are also being activated in Pierce County. Starting Tuesday, Aug. 16, newly installed ramp meters will be activated at the State Route 7 (Pacific Avenue) on-ramps to westbound State Route 512 and at the Steele Street on-ramp to westbound SR 512. These meters will also be carefully monitored to see if modifications to the meter rate are necessary.


Helena said...

Traffic in I405 from Renton to Bellevue is already a nightmare. I can only imagine how bad it will become if WSDOT is able to ram an extortion toll lane on this section where we are in desperate need of the 2 general purpose lanes we were originally promised. The extortion toll lanes on the northern part have been a complete desaster and have made traffic much much worse. The Renton to Bellevue stretch is one of the worst stretches in the country because it only has 2 general purpose lanes in each direction. A joke! We are not going to let WSDOT continue this failed project down on our section of I405. We need the general purpose lanes!!!! Real lanes for Real People!

WSDOT said...

The following comment was originally submitted on 8/24/2016, but was incorrectly screened from publication. We review blog comments in conjunction with our comment policy for things like harassing or offensive language, spam which is often indicated by identical text repeated from previous posts, comments promoting or opposing any person campaigning for election to a political office, etc. You may read our full comment policy here. Upon further review, we determined that this post does not violate our comment policy and are now publishing the full text in its original form:

Jeff Gray - Wed 8/24/2016 2:35 PM

I fully expect you are working on a scheme in which the driver will have to drop a quarter into a machine to get the ramp meter to turn green as W$DOT is now the equivalent of a street corner bum.

WSDOT comment policy

Post a Comment