Streetsblog links to an essay on why social conservatives should support public transportation and walkable communities. It's a good thought, though I personally tend to be fairly skeptical of the notion that the vast majority of conservatives are truly interested in things like "family values" or "free markets" beyond their rhetorical utility.
And even if you give them the benefit of the doubt on that score, they still have to weigh those benefits against the "piss off a hippie" potential of continuing to support car culture.
Honestly, a better tack might be to play up the value of walkable communities when Obama establishes the New World Order, Jesus returns, global race war erupts, and you're forced to use your arsenal of stockpiled firearms to defend your family from roving satanist cannibals. Under such conditions, riding a recumbent or hopping on the bus will be much easier than scavenging for gas.