Even in soggy Seattle, fall storms slow down our commutes

KIRKLAND, Wash.-- We all know that bad weather has an impact on our already congested roads -- but do you know how much?

It's something that traffic data company INRIX has been looking into. They say traffic and weather are intimately intertwined around Puget Sound, mostly because we've got so many cars on a limited amount of roadway.

It's been 13 weeks since we've seen a really rainy day around Seattle with more than an inch in the rain gauge. With about 1,000 people moving to our region every week, that's about 13,000 people potentially on the roads who've never experienced a Seattle rainstorm.

"Newcomers should definitely slow down, but not too much," says Washington state native Anne Molitor. "Because the locals get upset with people who drive too slow in the rain."

The autumn rains have returned. And while the wetter spots along I-5 on Tuesday got about a third of an inch of rain, much more is on the way with stronger storms expected to bring three times that much later this week.

"Be careful," says Jennifer Doherty.

She's lived around Puget Sound since 1989 and has a teenager at home who's about to get their license. "It's surprising how many people in this area don't know how to drive in the rain."

The rain does have a measurable impact on our commutes. Federal transportation data shows rain reduces highway speed by about 10-11 percent. Whether it's a main arterial road or an interstate, INRIX says those slower speeds often mean the road or highway cannot hold as much volume of traffic in any given hour.

"No surprise, weather impacts how we drive," says Bob Pishue. He's the senior traffic analyst at INRIX. "The problem is we already have such significant levels of traffic congestion that even if people do drive a bit better in the rain, the rain has a big affect on our commutes."

The biggest effect:  unreliability. Pishue says you just have no idea how long your commute is going to be. He says data from hundreds of thousands of GPS and mobile devices shows the lower visibility, slower road speeds, and more frequent accidents that come with rain means your regular commute could be twice or even in some cases three times as long.

"Anytime you introduce those factors you're generally sitting in congestion longer both in minutes and in miles," says Pishue.

Pishue says we can all be smarter commuters by checking your car for bald tire treads and replacing your windshield wipers twice a year. And something Jennifer Doherty who drives a dark colored SUV tells the soon-to-be driver in her home-- drive with your lights on during rainy days.

"My lights come on automatically all the time, I really like that because it really does increase visibility."

Another tip that Bob Pishue recommends is using the real-time traffic technology that exists on many apps, including the one you can get for free from Q13. And he says don't be afraid to take the surface streets if the freeway is totally jammed.

This next storm coming looks like it will not only be wetter-- but windier too, with wind gusts between 40-50 mph. That's strong enough to knock branches into power lines. So, be prepared for power outages.

If you encounter a traffic light that's not working--to treat it as a four-way stop. And, of course, remember on stormy days that you can livestream Q13 News programs right on your mobile device, even if there's no power at your house, to get the latest information to keep you and your family safe.