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Originally published November 7, 2010 at 10:00 PM | Page modified November 8, 2010 at 9:42 AM

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I-5 'smart signs' cut crashes, not travel times

Interstate 5 remains congested, but some early evidence suggests the high-tech "Smarter Highways" network is accomplishing its primary goal: to reduce collisions.

Seattle Times transportation reporter

As thousands of South End drivers can attest, traffic is still reliably slow where Interstate 5 enters downtown Seattle, despite the state's much-hyped "Smarter Highways" signs that switched on in August.

Yet some early evidence suggests the high-tech network is accomplishing its primary goal, which is to reduce collisions.

A total 35 crashes occurred in the seven-mile stretch between Tukwila and Interstate 90 from Aug. 10 to Nov. 1, compared with a range of 100 to 140 wrecks between Aug. 10 and Nov. 10 the past five years.

The comparison is unscientific, but it does suggest the $24 million investment in variable speed limits and electronic lane closures is helpful, said Dave McCormick, assistant regional administrator for the state Department of Transportation (DOT).

Another group of signs will begin operating above Highway 520 next week, and on the I-90 floating bridge next year, for a total $42 million. A simpler variable-speed system already exists on the I-90 bridge and on Snoqualmie Pass.

What the signs on I-5 haven't done is to make a measurable dent in congestion.

DOT officials are very cautious about claiming a congestion benefit this early, said Mark Hallenbeck, director of the Washington State Transportation Center.

But, he said, "If they have fewer accidents, they should eventually have better travel times."

Seattle was the second U.S. city, two weeks after Minneapolis, to activate such a system, borrowing strategies from Britain and Netherlands.

A main reason to test it on this particular stretch is that its chronic congestion generates about two-thirds of collisions, as drivers smack into the slower cars ahead of them.

Every half-mile, signs appear above all I-5 northbound lanes. The speed displays take one minute to react to changing road conditions.

Limits vary between 40 and 60 mph. When a car stalls, that lane is closed by an overhead red X. From 1/2 to 1 ½ miles back, drivers see an arrow and instructions to "merge" to another lane.

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It's better than the old way, where troopers heard the squeal of braking tires by surprised drivers, said Capt. Steve Burns of the Washington State Patrol.

"What we're seeing is, people are moving out of the closed lanes, so it's definitely creating a safer buffer," he said.

Still in jam

Drivers are constantly asking what's the point of having a sign that says 40 mph, when I'm stuck in stop-and-go traffic?

"I have not figured out the purpose of the variable-speed-limit sign when you hit a traffic jam," says commuter Lisa Coker, of Fife. "Slowing down to 50, going northbound, coming up to the Michigan Street exit at the north end of Boeing Field, does nothing to the traffic when it slows down to 30 mph at that point."

The first answer, says McCormick, is that 40 mph becomes the legal maximum, and troopers have handed out speeding tickets. (Minneapolis' speeds are merely advisory.) As with any road, drivers must react safely to conditions. Nonetheless, even an inflated "40 mph" figure still gives a clue congestion is ahead.

Second, the signs can be only so precise. "A lane that was doing 30 a few seconds ago might be going 10. It's really dynamic," McCormick said.

Traffic control

The gods of Seattle traffic are actually young engineers who baby-sit screens of computer code, four-color congestion maps and cameras inside the regional traffic-control center in Shoreline. When a fender-bender blocked the carpool lane near the Tully's headquarters at 4:05 p.m. Tuesday, engineer Maan Sidhu leapt and pointed at the video feed.

The squad instantly turned on a red X, the lane emptied for a half-mile, and a pair of State Patrol cars swooped in. A trooper stopped all lanes and pushed the car to the Edgar Martinez Drive exit.

A little way back, a red van straddled the X lane and the next lane — a vigilante move to block anybody from taking cuts. "People shouldn't do that, but it gets pretty wild out there," said Morgan Balogh, regional traffic-operations manager.

Traffic quickly reached a true 40 mph for a half-hour, an unusual afternoon treat.

Then a minor wreck blocked a center lane. This time, several motorists coasted under the red X. As a DOT truck nudged the stalled car aside, a black sports car swerved around and almost hit them.

There haven't been many drivers using closed lanes, but if that becomes a trend, state troopers will react with strong enforcement, Burns said. Troopers can issue $124 tickets to drivers in a closed lane.

Besides tackling daily wrecks and stalls, on the night of Oct. 20 Balogh set a series of red Xs over the entire freeway to help the presidential motorcade enter from Boeing Field.

An episode last Wednesday morning showed weakness in the system.

A sign at Southcenter said the trip downtown would take 15 minutes, at 9:30 a.m. It wound up taking 46 minutes.

The culprit was eastbound Highway 520, where drivers were blinded by sun glare and tapped the brakes, said spokeswoman Patricia Michaud. The stop-and-go was still extending its way south toward Beacon Hill right before 9:30 a.m., and DOT didn't catch the trend in time to inform drivers so they could detour using Highway 599.

Efficient pavement

These and other lane-management schemes, including tolls, are part of an international trend to use pavement more efficiently, instead of spending millions to add lanes that eventually fill up.

Washington's DOT compares traffic to grains of rice. If you dump a liter of rice into a funnel, it gets stuck. If you pour it gradually, the rice flows to the bottom quicker.

So if motorists merge early, instead of changing lanes at the bottleneck, cars are supposed to flow more smoothly overall.

McCormick could be even more aggressive, and restrain speeds back at Tukwila, so that people drive 40 mph the entire seven miles. But he doesn't want drivers to be frustrated and flout the signs long before the actual congestion.

European experience suggests a 3 percent drop in congestion with the signs, he said.

It will take three years to gather statistically valid data on I-5, said Hallenbeck. Variables such as weather, the new Link light-rail line and even slumping Seattle Mariners attendance affect traffic, he said.

In the future, Highway 99 construction and tunnel tolls would divert drivers to I-5 and other routes.

Some frustrated motorists wish the state would simply widen the funnel, by adding lanes under the convention center. The state has studied ideas such as putting buses on the right shoulder near 520, or changing the road layout at the left-side Seneca Street exit.

Even if I-5 tolls deter some cars, DOT says the freeway through central Seattle is so narrow that traffic-management signs will always be needed.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com

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