I don't know about the 50s, but by the sixties traffic was as bad in some places as it is today. Traffic in Southern California, where I grew up, is actually better today than it was in the 70s.
That's about when it started getting bad. The term "Sig Alert", for an unplanned lane closure, originated in LA in 1955. It takes its name from Loyd C. "Sig" Sigmon, who created a radio-based notification system for the California Highway Patrol:
Sigmon developed a specialized radio receiver and reel-to-reel tape recorder. When the receiver picked up a particular tone, it would record the subsequent bulletin. The device cost about $600. The LAPD's chief, William H. Parker, was interested, though skeptical, warning the inventor, "We're going to name this damn thing Sigalert." More practically, he refused to use it unless the receivers were made available to all Los Angeles radio stations — it could not be a KMPC monopoly.
Bad traffic was mostly limited to a few large cities such as LA then. In most of the US, it was not nearly as bad.
It was also believed that traffic was a fairly minor infrastructure problem that could easily be resolved by widening the highways, adding a few more lanes here and there. (Turns out that when you add lanes, it just causes that many more people to drive on that road, but this was not yet widely apparent at the time.)
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