legislative
Department of Education and each state has a State department of education.
Speed limits are set by whatever level of government owns that particular roadway.
The federal government sets national speed limits by promising monetary incentives to states that cooperate with their legislature. The states can set their own limits but if they want aid from the federal government they must comply with their mandates.
As a fuel saving measure during the oil embargo crisis.
Speed limits aren't in the Constitution. If you wanted to really reach you could say the 10th--any powers not reserved to the federal government devolve to the states--but that would be a big stretch.
states
Parts of the German Autobahn do not have posted speed limits.
Yes Germany does have speed limits but on a lot of motorways they dont :)
They are not allowed to exceed speed limits
Drivers need to be consciously aware of changing speed limits and watch for posted signs in city and suburban driving environments. You would expect: A speed limits of 15 mph B speed limits of 25 mph C speed limits of 35 mph You would not expect to see D speed limits above 45 mph City driving is referred to as "start and stop" driving because traffic is either moving or stopped. Changing speed limits can make traffic slow to a crawl, such as in school zones.
Posted speed limits tell you what the maximum speed is on that specific road. That is the speed that you are legally able to drive on the road.
The Government, through the Department of Transport, is responsible for setting the national speed limit. The national speed limit depends on the type of road - motorways being 70 mph. Local authorities are able to set local by-law speed restrictions.