I think it depends on the individual circumstances. For some it may not be cheaper. If you live close to work and park for free it would be hard to justify, although I'd still work the math.

In my case though, @ $65 a week in tolls, and $120 a month in parking not to mention the wear and tear on the car it's easy to justify. That said however, it would be cheaper if I would stop buying expensive bikes and accessories