Would a monorail — also rubber tires on concrete — perform better?
A consulting engineer for the Seattle Monorail Project's Green Line says it would. "If you're sitting in traffic, you're going to feel pretty envious if you see the comfortable monorail trains running overhead," said John Conley of Lea + Elliott, which worked on an airport monorail in Newark, N.J.
But because the concrete monorail tracks would be elevated, they could freeze as quickly as a highway bridge.
"There's nothing magical about having concrete guideway or rubber tires in the air," said project opponent Richard Borkowski, president of pro-light-rail People For Modern Transit.
The reassuring feature of a monorail is that it wraps around its track, so there is no risk of skidding side-to-side like a bus or car. The question is whether trains would slip lengthwise and overrun a station or spin their wheels climbing a slope.
Freezing weather presents two challenges: to keep electricity flowing to the trains, and to maintain traction between the enclosed rubber tires and the concrete guideway.
Power for the monorail is supplied by a conducting metal strip that rubs against carbon pads onboard the train. Accumulated ice would insulate the strip, blocking the flow of power, Conley said.
To prevent that, Green Line construction teams will be required to attach a heating cable, at a cost of $3.5 million, to warm the power strip. The basic principle is akin to the rear-window defroster in a car.
"On a morning like this, you'd just simply flip the switch that would absolutely prevent icing on the power rail," Conley said.
Slippery concrete is a more complicated matter.
Monorail officials have talked about building heating equipment into guideways, but Conley's report estimates the cost at $1.3 million a mile, or $18 million overall. Newark has such a feature, but leaks and electrical flaws forced a retrofit in 2001, at the expense of the contractor.
Instead, Conley recommends a cheaper strategy: using the trains themselves to prevent ice buildups by running them continuously for 24 hours on the coldest days. The maintenance crew, which would be doing overnight work anyway, would supervise the de-icing patrol.
Under ordinary conditions, the monorail would close for at least four hours each night.
"Just the operation itself creates enough friction on the rubber tires" to melt the ice, Conley said. However, his written report warns that "it is not effective for large accumulations or when ambient temperatures are substantially below freezing."
For more severe conditions, he suggests that a maintenance train be fitted with rotary brushes to knock away snow, at a cost of $20,000. The vehicle also would deposit chemicals or salt on severe days, as the Seattle Center Monorail does now.
The chance of those materials or snow falling on pedestrians below is "a significant issue," the report acknowledges.
Construction teams will be required to guarantee that trains run 99.5 percent of the time during scheduled hours or take financial penalties.
"They have to do whatever it takes to meet availability, so if they believe further mitigations are needed for ice and snow, the burden is on them to do that," Conley said.
While the old Seattle Center Monorail route is flat, the Green Line route from Ballard to West Seattle includes steep climbs. There is a 6 percent grade between the Safeco Field station and Sodo, and a 120-foot-high crossing of the Lake Washington Ship Canal.
Seattle transportation director Grace Crunican said that at some point in the planning, she would expect the monorail agency to propose "state-of-the-art" ice-prevention methods.
"In most cities," Crunican added, "rail is your best friend in inclement weather."
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org