Proposed 11-foot lanes not new for commuters
Driving along the freeway, does it seem like the Kenworth, Hummer or Expedition next to you is a bit too close? Wonder what it would be like if the lanes were a foot narrower?
To add more high-occupancy-vehicle lanes to the Interstate 90 floating bridges, planners have proposed shrinking some lanes from the standard 12-foot width to 11 feet, with narrower shoulders. While the idea may unnerve some motorists, it's hardly new.
Just take a spin on Interstate 5 through Seattle, where about half of the freeway already operates with the smaller lanes. Narrow lanes exist in several regions, including Atlanta, Los Angeles, Dallas and suburban Washington, D.C.
The plan for I-90 would target a seven-mile stretch between Rainier Avenue South and Bellevue Way Southeast. Sound Transit, the state Department of Transportation, and the cities of Bellevue and Mercer Island have persuaded federal highway officials to consider including 11-foot lanes in an $80 million project to be completed in four years.
The restriping would allow one more high-occupancy-vehicle (HOV) lane in each direction — giving buses and car pools a quicker "reverse commute" from Seattle to the Eastside in the morning and home in the afternoon.
In each direction there would be a 12-foot-wide HOV lane, two 11-foot lanes and a 12-foot lane. The center express lanes would continue to carry Mercer Island traffic, transit and car pools.
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However, a state consultant's analysis of 11-foot lanes in the Seattle area and other regions predicts putting them on I-90 would cause 175 more traffic accidents per year — a figure that could be cut to 20 or 30 if suggested safety measures were added, such as lowering the speed limit to 50 and adding better lighting, rumble strips and 24-hour towing services to immediately clear stalled vehicles.
In South King County, where much of I-5 already has 11-foot lanes, the State Patrol has not seen an increase in accidents or other problems related to lane width, State Patrol Trooper Monica Hunter said.
Even when lanes are only 11 feet wide, a typical car — about six feet wide — has more than two feet of wiggle room on each side, though some larger vehicles, such as school buses or tractor-trailers, have only a foot or so.
Some lanes are even narrower. On the Aurora Bridge, the center northbound lane is 9 feet, 3 inches wide. The other lanes on the bridge are 9 feet, 6 inches wide to 9 feet, 8 inches. Some lanes of the Alaskan Way Viaduct are 9 feet, 6 inches wide.
The Seattle Transportation Department thinks narrow lanes can frazzle the average motorist. That's why the city plans to construct a second Spokane Street Viaduct so people driving from West Seattle to I-5 can travel on standard lanes instead of 11-foot lanes with no shoulders.
And in South King County, the 11-foot lanes of I-5 are being expanded to full size under a state agreement with the Federal Highway Administration.
The agency's Jim Leonard, an urban-transportation and environmental engineer, concedes that when he drives north from Olympia, inattentive drivers and worsening congestion make him more jittery in 11-foot lanes.
"People make mistakes all the time; the penalty shouldn't be death or a catastrophic crash," he said.
The Seattle-Bellevue stretch of I-90, with full-width lanes and 10-foot shoulders, has fewer crashes than average for urban freeways; federal officials are reluctant to mess with a good thing.
I-90 has only 87 collisions per 100 million vehicle miles, compared with an average of 106 wrecks on 11-foot lanes in Washington state and 154 on an Atlanta freeway where lanes were narrowed for an HOV project.
Portions of Interstate 84 in Portland, I-395 in Virginia and I-405 in Los Angeles with 11-foot lanes fared as well as I-90 or nearly as well, according to data analyzed by HNTB, an engineering firm doing safety studies for the state Transportation Department.
Mark Hallenbeck, director of the Washington State Transportation Center at the University of Washington, said tighter lanes are not necessarily more dangerous if they coax people out of their psychological comfort zones.
"If 11-foot lanes cause people to pay more attention while driving, they will be safe or safer than the existing 12-foot lanes," he said.
I-90 drivers have navigated narrower lanes before. When the original eastbound floating bridge was closed for reconstruction from 1990 to 1992, cars were diverted to the new bridge that today carries westbound traffic and express lanes. Three 11-foot lanes and a 10½-foot HOV lane went west and three 11-foot lanes east, under a 50-mph speed limit.
The result? Collision rates declined westbound, winding up 23 percent lower than under the present layout.
But the eastbound collision rate was twice as bad. The HNTB analysis suggests the westbound section fared better partly because four lanes reduced congestion.
If the proposed lanes were added to I-90 without safety improvements, 465 to 515 crashes are projected for the first year compared with 290 to 340 (not counting express lanes) under a no-build option.
Part of the increase in accidents would be caused by the increase in traffic the redesigned bridges would attract, the study indicates. But with lower speed limits and other changes, the crash rates would fall to around 367 a year, only slightly worse than now, the analysis says.
Mike Lindblom can be reached at 206-515-5631 or mlindblom@seattletimes.com.