In the interminable battle against traffic, a growing number of government and private initiatives offer U.S. drivers high-quality real-time traffic data and even short-term predictions of travel time from, say, one freeway intersection to the next.

But most of the forecasts don't extend beyond 15 or 20 minutes. Though a veritable traffic jam of companies has sprung up to offer data, they generally inform commuters of snarls as they occur, which is often too late for drivers to change their plans.