As I sit here on a corporate shuttle, the bay area is under its third "spare the air" day. This article
asks whether it matters and makes a difference. Looking at traffic my sense is that it might make it worse.
The loss of federal funds to encourage mass transit are no longer provided and with gas cheap the incentives aren't sufficient. I find that more the reason. For most people a car is a sunk cost so they can't utilize it they are "losing" money and a car is something that you pay a big chunk each month only second to rent or mortgage.
Perhaps raising tolls on spare the air days might create greater observance.
A side note. Cars are the dominant species in many ways. While writing this a young woman was at a crosswalk and only one car stopped to give her right of way.
The challenges of the environment remind me of weight loss. We don't get fat all at once but we want to lose it all at once.