Quite apart from the equity issues associated with treating car and transit modes equally, it’s worth pointing out that keeping the overall deduction level at $240 per month seems on its face like terrible public policy.
The vast majority of transit users are spending much less than that on their tickets and passes*, so most of the deduction isn’t of much utility. On the other hand, it’s probably not the worst thing in the world to turn a few long-haul drives into commuter rail trips.
Meanwhile, show me a place where employees pay $240 a month to park, and I’ll show you a place with severely constrained car capacity and robust transit alternatives.
Given the current federal fervor for austerity and closing tax “loopholes,” it seems like a broad-based reduction in this tax deduction would have positive impacts on congestion and transit use in the most ideal transit markets, while creating little grief at workplaces that are essentially unserviceable for transit. In an ideal world we’d let the transit subsidy be higher than the parking one, but cutting both is the next best thing.
* I tried to get more precise numbers from APTA, but no luck.