A top-notch economy requires a top-notch infrastructure. Yet in the U.S., roads are crumbling. In the past 25 years, miles traveled by car or truck have doubled, but total highway length has barely budged–one reason the World Economic Forum ranked American infrastructure a troubling 24th out of 124 nations. “We’re not in the back of the pack, but we used to be in the front, and we’re falling,” says Edward Alden, a senior fellow at the Council on Foreign Relations, which has released a new report on the issue. (See the report at www.cfr.org/roadtonowhere.) Meanwhile, South Korea,…