by guest blogger Bart Treece

Whether it’s a weekend 520 bridge closure or people leaving a football game, we hear this question fairly often and usually from folks who were stuck going the opposite direction of the express lanes.
The simple answer is that the reversible, congestion-fighting powers of both the I-5 and I-90 express lanes add capacity to the direction of travel that can benefit the most drivers. Or, to put it another way, the direction with the most cars, wins. The decision to flip the switch and add lanes doesn’t come from a whim, a guess or a coin toss. It’s driven by hard numbers collected by sensors in the roadway and crunched by traffic engineers, (engineers love numbers).

Take for instance I-90. More people are heading westbound into Seattle during the weekday morning and vice-versa for the afternoon and evening commute, which is why the express lanes are switched to add lanes to all those drivers. During a weekend-long 520 bridge closure, I-90 is the go-to route for people trying to get across Lake Washington. Since our traffic sensors record the number of cars on the road, we know more people take I-90 westbound into Seattle from morning until early afternoon, and vice-versa for eastbound later in the day.

Not so, say some folks who were stuck westbound near Mercer Island late on a Saturday. Darren posted this on our Facebook page, “WSDOT, why not open the WEST bound express lanes on I-90 tonight? 520 is closed and EVERYONE is headed into Seattle. It's a parking lot out here and EAST bound is wiiiiide open.”

Driver feedback is important to us, so we checked the numbers. If we made a mistake, we want to know about it. Turns out, we made the right call. When Darren noticed the stark difference in east and westbound traffic flow, eastbound I-90 had an average of 600 more cars per hour. Anything that blocks the roadway, like a stalled car or a crash can also throw traffic flow out of whack, which is what happened the Saturday night Darren tried to make his way into Seattle.

We also hear from sports fans who want the express lanes to take them to a game at CenturyLink Field and then back across the lake after the final whistle. Sometimes we will, if the extra fans plus the typical normal users will create a larger demand. But, if we know more people will be heading the opposite direction of sports fans, the I-90 express lanes will be there for the majority of drivers. For example, we sometimes get a Monday Night Football game. Look, we love the ‘12th Man’, but during the weekday our first consideration is for the people who use the lanes regularly to get home from work, so we keep them eastbound for commuters.

What about I-5?

The other set of express lanes to consider is on I-5. These lanes are a great way to pass by a lot of Seattle-related traffic and they’re used mostly by folks who just want to get through downtown. If you’re trying to take the I-5 express lanes to CenturyLink Field, your only option is exiting before the stadium at Cherry/Columbia or afterward near Tully’s. Either way, you have to fight surface-street traffic, which doesn’t really help you.

We’re always reviewing traffic patterns to see if we can make improvements, because they can change. We want people to get to the game on time and home safely. We will make some changes with the upcoming UW Huskies and Sounders FC games, keep an eye on the schedule and plan ahead. Switching both the I-5 and I-90 express lanes help us manage traffic congestion and can make for a smoother ride.