WHETHER THE federal government should give a tax break to workers to help pay for their commutes is a question that is certainly worthy of discussion. What shouldn’t be on the table is giving a bigger edge in any subsidy to those who drive, as opposed to those who use mass transit — since there is no reason to encourage more traffic, more pollution and more gas consumption. That, however, will be the outcome if Congress doesn’t act before it adjourns for Christmas.

At issue is a program started in the ’90s that allows workers through their employers’ benefits packages to set aside money before taxes to help offset the cost of their commutes. The amount has changed year to year, but for reasons that simply make no sense (we’re pretty sure politics were at play), workers who parked were able to set aside roughly twice as much as commuters who used public transportation. The 2009 stimulus package brought much-needed parity, allowing $230 to be set aside each month for both parking and transit. Without congressional action, though, the transit benefit on Jan. 1 will drop to $125 a month, while the parking rate will increase to $240 a month.

Congress, clearly preoccupied with the debate over extending the payroll tax cut, seems to have given little thought to the consequences of its inaction. Some 3 million people nationally participate in the program, and transit advocates say the more expensive ride will likely cause a decline in public transportation use. Washington’s Metro, for example, is projecting a nearly 3 percent reduction in rail ridership and a $16 million drop in annual revenue. The cost of extending the benefit is estimated at $158 million in 2012, according to Congress’s Joint Committee on Taxation.

That seems a small price to pay for getting people out of their cars and onto buses and trains. But if cost is an issue, there are ways to make the change revenue neutral — and a good place to start is with a reexamination of the parking benefit. The argument for the transit benefit is grounded in the fact that increased use of public transportation benefits everyone — even those who choose to drive because there are fewer cars on the road. No such argument can be made in subsidizing the parking costs of those who drive to work. Workers can choose to drive and park — but there is no public interest in government picking up part of the tab.