At least 60 feet across.

Some are two, some are four I have seen five and six lanes which counts as ten or twelve if you count both sides. The autobahn has nothing on us.

There is no standard width for highways currently in existence. construction of new highways has proscribed standard lane widths that are set by the jurisdiction that builds them (i.e., in california, state highway lane widths are mandated by Caltrans, other states have their own standards). There may be a Federal standard in place now.

I think that standard lanes are about eight feet. Vehicles and trailers need a special permit if they are more than eight feet wide. Tractor trailers are about eight feet wide and they fill the lane.