Hitler's initial vision for the Autobahn Project.

An automobile on the sweeping curves of the Autobahn with view of the countryside (Library of Congress)

Clearly Hitler envisioned the Autobahn construction project  as a domestic, not military imperative.

Taken from David Irving's Hitler's War, 2002 edition:

During the months in Landsberg prison Hitler had mentioned one particular ambition, the construction of a network of superhighways. Schwerin von Krosigk would write: 

Hitler used to describe how the city folk returned from their Sunday outings in overflowing trains, getting their buttons torn off, their hats crushed, their good mood ruined and every benefit of the relaxation wasted; how different it would be if the city workers could afford their own cars to go on real Sunday outings without all that. . . Road-building has always been the sign of powerful governments, he said, from the Romans and the Incas down to Napoleon. 

Only twelve days after the seizure of power in 1933, Hitler announced the autobahn construction program; on June 28 the Cabinet passed the law, and a few days later he sent for Dr. Fritz Todt, an engineer who had written a 48 page study of the problems of road-building in 1932, and asked him if he would like the job of Inspector-General of German Road Construction. He said he had always preferred travel by road to rail, as the contact with the people was closer: ‘I must have driven half a million miles in my fourteen years of struggle for power.’ Todt accepted the job: the interview lasted barely three minutes. In July,  Hitler again sent for Todt, strolled for ninety minutes with him, told him what routes the first net- work would take, laid down the minimum width of the traffic lanes, and sent Todt to begin work at once. (All this emerges from Todt’s own private papers.) The military importance of the autobahns has been exaggerated. The German railroad system was of far greater significance. For the present, the autobahns were the means whereby Germany’s national unity could be enhanced, because Hitler realized that the fight against provincialism and separatist trends would last for many years yet.