I rode the bus in today early. I get a lot of thinking done on the bus, but it's languid, unfocused thinking. Conscious dreaming, but not exactly daydreaming. Public transit is great for dharma practice. Because I have no control over the speed at which I can travel, I have that much less ego to surrender. If I'm stuck in heavy traffic, it's not my fault; if there's an accident, it's not my fault; I might die, but at least it won't be my fault. BAM! No ego.
Commuting by bike is exactly the opposite. Nothing but freedom. Traffic provides no friction, so the only variables affecting my commute are the mechanical integrity of my bike (for which I am responsible), and my own physical strength. So every action provokes an immediate effect. This surfaces karmic law in a really tangible way: any interaction with other beings (vehicles) will cause immediate and obvious effect. So that keeps me focused on skillfull practice.
I almost never commute by car. I live too close to downtown, it would be silly to drive such a short haul. But I did it a few times when I working in Hillsboro. Automotive commuting is samsaric; illusory and ego-reinforcing. I feel like I'm in total control (because I can change gears and push the gas pedal?) but in reality I'm a hostage to traffic. Car commuting makes the noble truths apparent: I desire to go faster, and from this I suffer. Of course you do it over and over and over, day after day, an endless cycle of suffering.