BART officials announced Wednesday that a new train wheel design they hope will cut noise by half has passed a battery of performance tests at its Hayward test track and will be introduced into service gradually starting early next year.
For decades, the system’s train cars have operated on a perfectly flat wheel profile, originally intended to assure a smooth ride at high speeds. But those wheels vibrated, causing tiny ruts in the rail and howling on straightaways. They also slipped on turns, causing screeching.
The noise – which can reach 90 decibels, the same as a motorcycle from 25 feet away – has long driven passengers to distraction.
The newly designed wheel is less noisy, BART says, in part because it is thicker in the middle and thinner on the outside. The so-called modified tapered design allows the wheels to handle curves more efficiently and smoothly while limiting the vibration that caused the ruts on straightaways.
To the untrained eye, the difference is barely perceptible.
"It's a computer generated shape," said Ben Holland, BART’s manager of vehicle systems engineering. "It is very subtle but it’s very effective."
NBC Bay Area first reported on the breakthrough in May. Now, after preliminary testing showed that the new design met performance and safety standards, Holland says it is time for the real test.
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Early next year, BART will begin retrofitting its existing fleet with newly resurfaced wheels that match the tapered profile. The rollout will take three years and will come at a time when BART plans to introduce 775 new train cars that come equipped with the new wheel profile designed by engineers with Bombardier.
Alicia Trost, a BART spokeswoman, says some cars with the existing fleet of 669 cars will get new wheel designs when their old wheels wear down. Some will simply be replaced with new cars.
Holland says he hopes the expected sound reduction will not be immediate, in part because the reconfigured quieter wheels will be mixed with cars that have the older, existing wheel design.
BART hopes the conversion will begin in seven months and ultimately, the new wheels will cut train noise in half. The new design comes with an added bonus: Holland believes they will last five years, twice the durability of the current wheels that only last two and a half years.
