A Sound Transit railroad locomotive carrying commuters home to Lakewood on Tuesday evening turned out to be the little engine that couldn’t.
The train lost traction on the steep grade between Freighthouse Square and M Street in Tacoma about 5:30 p.m., briefly stranding seven cars and about 100 passengers.
Engineers were unable to make it up the hill after two more tries and ended up backing down to the Tacoma Station, where passengers had to disembark and wait about 30 minutes for the next train.
Sound Transit officials said Thursday the locomotive’s wheels began spinning when an automatic device that’s supposed to spread sand on slippery rails failed to operate correctly.
“This was a one-off, an aberration,” said Eric Beckman, Sound Transit’s rail project manager. “There was a fault in one of the sanders. It’s not the sort of problem we will encounter regularly, by any means.”
Beckman said all Sounder locomotives are equipped with sanders controlled by computers designed to track the relationship between the speed of the wheels and the speed of the train across the ground.
When the computers sense wheels are losing traction, dispensers are supposed to drop sand in front of the wheels, increasing the friction and adhesion.
The grade on the 1.4-mile section of track between Freighthouse Square and M Street is 2.85 percent, the steepest in the Sounder system and among the steepest in any passenger rail system in the country.
Before the Lakewood link opened Oct. 7, engineers repeatedly tested trains on the grade, Beckman said, making sure they were up to the task.
“We modeled going both up and down the hill, and we were aware that in adverse conditions you’d have to take extra precautions,” Beckman said.
No trains shorter than a locomotive and three cars are allowed on downhill runs, he said, because they don’t have enough braking capacity.
For the uphill runs, Beckman said, Sound Transit considered adding extra equipment, including snow blasters for clearing snow, hailstones and dead leaves, but decided that was not necessary.
The steepness of the grade dropping to Tacoma’s downtown waterfront has been an issue for railroads for more than a century.
An early Tacoma trolley line that made roughly the same descent was the site of one of the worst streetcar accidents in U.S. history. On July 4, 1900, an overcrowded trolley car jumped the tracks on the old C Street trestle, killing 43 people.