[perpetualcrayon]

Some folks I've talked to disagree but I think not an insignificant reason is ubiquitous usage of GPS and the internet (knowing precisely where to go and how to get there in the most efficient way possible).

EDIT: and then I figure another leap was the convergence of the two. gps/internet on cell phones.

[lucidguppy]

You mean not getting lost is causing more efficient travel?

[kodablah]

Or increased availability of traffic information allows people to avoid it easier by waiting or changing routes.

[joncrane]

People are also taking the shortest/fastest routes now where before they just took the way they knew got them there.