PADERBORN, Germany — When inspectors decided a few months ago that the aging bridge over the Kiel Canal in northern Germany was too weak for heavy truck traffic, Holger Dechant, hired to deliver giant wind turbines to the other side, was at a loss.

He did eventually come up with an alternative route. But it is telling of the sorry state of some of Germany’s roads and bridges: His company is driving the turbines to a ferry, shipping them north to Denmark and then driving them south again back into Germany.

“That’s how bad it is,” Mr. Dechant said recently, explaining the 186-mile detour in his office here. “We just haven’t invested enough. And now there is trouble because there is no easy button to fix it all.”

Germany was once known for its superfast autobahns, efficient industry and ability to rally public resources for big projects, like integration with the former East Germany. But more recently, it has been forced to confront a somewhat uncharacteristic problem: Its infrastructure — roads, bridges, train tracks, waterways and the like — is aging in a way that experts say could undermine its economic growth for years to come.