Driven by high gas prices and an uncertain economy, Americans are turning to trains and buses to get around in greater numbers than ever before. But the aging transit systems they're riding face an $80 billion maintenance backlog that jeopardizes service just when it's most in demand.

The boost in ridership comes as pain at the gas pump and the sluggish economic recovery combine with a migration of young adults to cities and new technology that makes transit faster and friendlier than in the past. The number of transit trips over a 12-month period will likely set a new record later this month or next, say Federal Transit Administration officials. The current peak is 10.3 billion trips over a year, set in December 2008.

But decades of deferred repairs and modernization projects also have many transit agencies scrambling to keep trains and buses in operation. The transit administration estimated in 2010 that it would take $78 billion to get transit systems into shape, and officials say the backlog has grown since then.