City Hall
Extra Fizz: McGinn's 520 Plan Could Allow Eight Lanes of Traffic
A plan supported by Mayor Mike McGinn to design a new 520 bridge to accommodate light rail could have an unintended result: Because the bridge would be ten feet wider under McGinn's plan, it would be wide enough, at 125 feet, to accommodate eight lanes of traffic.
Tim Payne, a planner for Nelson/Nygaard, the company that studied the challenges to putting rail on the bridge, confirms this, saying that the only change that would be necessary is reducing the size of the outside shoulders from 10 to eight feet. "If one plays with the shoulder width, it is possible to [build] eight 11-foot lanes," Payne says. Similarly, planners could reduce the bike lanes from 14 feet to 10.
Although the state has standard widths for lanes and shoulders, projects violate them all the time—for example, on Mercer Island, I-90 has 10-foot bike lanes and outside shoulders just four and eight feet wide. And Payne says "conversations are going on about how to push [the width of the bridge] down even further," by taking away some space from light rail and reducing the size of the shoulders.
Obviously, McGinn isn't proposing eight lanes for cars on the 520 bridge. He's proposing four lanes for cars and buses and two wider lanes in the center that would start out as bus rapid transit lanes and eventually be used by light rail.
But—also obviously—political winds have a way of shifting, and transportation leaders in the state legislature tend to see highway expansion, not transit, as the best solution to traffic congestion. Road-expansion proponents have long argued that HOV lanes are "wasted space" because carpools and buses whiz by while single-occupant vehicles sit at a standstill. If traffic across the lake gets worse, dedicating those "underutilized" lanes to cars is going to look a lot more tempting.
Tim Payne, a planner for Nelson/Nygaard, the company that studied the challenges to putting rail on the bridge, confirms this, saying that the only change that would be necessary is reducing the size of the outside shoulders from 10 to eight feet. "If one plays with the shoulder width, it is possible to [build] eight 11-foot lanes," Payne says. Similarly, planners could reduce the bike lanes from 14 feet to 10.
Although the state has standard widths for lanes and shoulders, projects violate them all the time—for example, on Mercer Island, I-90 has 10-foot bike lanes and outside shoulders just four and eight feet wide. And Payne says "conversations are going on about how to push [the width of the bridge] down even further," by taking away some space from light rail and reducing the size of the shoulders.
Obviously, McGinn isn't proposing eight lanes for cars on the 520 bridge. He's proposing four lanes for cars and buses and two wider lanes in the center that would start out as bus rapid transit lanes and eventually be used by light rail.
But—also obviously—political winds have a way of shifting, and transportation leaders in the state legislature tend to see highway expansion, not transit, as the best solution to traffic congestion. Road-expansion proponents have long argued that HOV lanes are "wasted space" because carpools and buses whiz by while single-occupant vehicles sit at a standstill. If traffic across the lake gets worse, dedicating those "underutilized" lanes to cars is going to look a lot more tempting.
