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.
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.
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.|
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.