As recently as last year, the ride between BART’s Glen Park and Balboa Park stations was a screeching cacophony, as the rail system’s old cylindrical wheels scraped on its corrugated rail.

Now, that journey is about 20 decibels quieter, Greg Shivy, the principal track engineer, said during a recent presentation to BART’s Board of Directors. The difference, he said, is that between a roaring gas-powered lawn mower and a steadily thrumming dishwasher.

BART began shaving about 2 millimeters of metal off every wheel in its fleet two years ago, a simple solution to the head-splitting squeal a train makes as it roars along the track. That project is almost complete. The transit agency has whittled down wheels on 96 percent of its 669 cars, improving wheel-to-rail contact and reducing track rippling, which can cause the rail to decay. At the same time, BART is grinding rails throughout its system to make the ride smoother.

Noise complaints dropped by 73 percent during that two-year time period, and transit officials expect other benefits to follow. Charles Franz, a vehicle systems engineer, predicts that BART will save about $2 million a year with the tapered wheels. It will also double the life span of each wheel from four years to eight and reduce the amount of time trains spend in the shop getting their wheels repaired — from 26,000 lost hours a year down to 17,000.

Perhaps more importantly, the transit agency hopes to create a better environment for riders and the people who live along BART routes — particularly in West Oakland, where four lines run on an elevated track, creating a wall-to-wall soundtrack of clattering steel.

Residents and merchants in that neighborhood can finally keep their doors and windows open when a train rolls by, Director Lateefah Simon said. She called the wheel redesign an example of “the real, every single day, lived impact” of better engineering.

Director Robert Raburn noted that BART’s sound levels may also affect development in West Oakland, an area that BART lacerated when it built its trackway along Seventh Street in the 1970s. The area is finally attracting housing and commercial projects, but developers are worried that the constant rattle of trains might dissuade new residents or businesses from coming in, he said.

“They were looking for ways to mitigate the noise — and in the past the solution was always, ‘We’ll build a wall without windows,’” Raburn said in an interview. “Now it’s time for us to make good with folks. ... This is really a feel-good story.”

But the problem isn’t limited to one neighborhood. BART also goes above ground in East Oakland, El Cerrito, Daly City and many parts of suburban east Contra Costa County, and residents of those areas are all besieged by its tinny noise. The squawks seem worst in the Transbay Tube, which funnels thousands of passengers between the East Bay and San Francisco each day.

When a Chronicle reporter surveyed the BART system in 2010 with a handheld sound-level meter, he found that noise levels reached 100 decibels in parts of the Transbay Tube. That’s comparable to standing next to a jackhammer.

That became apparent to Director Debora Allen when her son sent a text with a screenshot of a decibel meter.

“He said, ‘Mom, I just went through the Transbay Tube on BART — this is horrible,’” Allen recalled. On the screenshot, the decibels “were in the high 90s,” she said.

It may take a while to significantly turn the volume down on that crucial segment, Shivy said. Noise in the tube comes more from the rails than the wheels, and they can’t be fully ground down until BART has converted to its new fleet of Bombardier cars.

“What we’re trying to avoid doing is jumping around responding to complaints,” said Tamar Allen, BART’s assistant general manager of operations. “We’re trying to be very systematic about it.”

Rachel Swan is a San Francisco Chronicle staff writer. Email: rswan@sfchronicle.com Twitter: @rachelswan