Cars also inflict many externalities onto others that other forms of transportation do not (pollution, increased travel distance, injuries and deaths, etc.), and yet drivers seem less keen on paying extra to compensate for those costs.
The biggest externality cost in the United States by far is parking. Many cities have mandatory parking space requirements for businesses that impact not just new developments but re-purposing of existing properties (ex: restaurants must provide so-and-so many free parking spaces per thousand square feet; you have to do this even if you're converting an existing property into a restaurant). This is a huge pain for a lot of people trying to open small businesses.
This is more of a zoning issue though (I think mandatory parking ordinances should be repealed and all parking should be privatized).
And wear and tear on the road is approximately proportional to weight and speed so bikes make almost no contribution to road wear, which is the primary cost of our road system.
About 29,000 people die from air pollution in the UK and about 1 in 4 of those may have been from traffic pollution. But death is cheap and people living longer with worse quality of life with COPD or similar costs money.
