Gas is 3-4x more expensive, sometimes more so, where I grew up. But it's really hard in the US, where distances are so great that it would hurt peoples' livelihoods in a meaningful way. I think we'd need a substantially improved public transport system first, which also requires a radical change in thinking.

On my last trip back, I was struck that I could take a bus to London - a 90 minute journey - roughly every 5 minutes during the day, and every 30 minutes at night. There was absolutely no need to drive: it would have been more expensive and less convenient. That's what it's going to take.

Bring on high-speed rail? But also commuter rail, and fully integrated transport, and the political will to wean ourselves away from cars altogether.