For more than 15 years, Liz Heffele has commuted via vanpool the 45 miles from her Antioch home to her job at workers' compensation law firm Laughlin, Falbo, Levy & Moresi in downtown San Francisco.

Now Heffele's commute costs less, thanks to the federal stimulus bill.

Under the 11-year-old Qualified Transportation Fringe commuter tax benefits program, money for BART and other alternative commutes can be set aside pretax by employers for employees. Under the stimulus bill signed in February, the pretax amount allowed for individual commuters nearly doubled, to $230 a month.

"For employees, it's an approximately 35 percent to 40 percent saving on their transit costs," said Steve Rossen, an account manager at Massachusetts-based Commuter Check, one of several companies that work with employers to administer the program.

If a commuter spends, say, $500 a month on commute costs such as parking, ferry trips, bus or BART, that commuter now doesn't have to pay taxes on $230 of those dollars.

"Additionally, it's a benefit to your employer because they're not paying FICA taxes on it," said Kit Powis of transportation information service 511.org.

"We have about 5,000 companies in the Bay Area participating," Rossen said.

The number may increase because the City of San Francisco mandated in January that companies employing more than 20 people in the city more than 10 hours a week must offer the benefit, Rossen said. Along with the boost from the former $120 monthly limit to $230, a $20 monthly biking subsidy was approved as well. It doesn't involve a pretax benefit, but rather a company subsidy.

To enroll in the program, employees should contact their employers' human resources departments. If the company isn't participating, 511.org. has an outreach program to help employers get started.