Some of the western US states used to have no upper speed limits, but they no longer do. In order to accept Federal Highway Funds they had to come into compliance and establish upper limits to the speed allowed on their highways.
No, not all 50 states raised the speed limit in 1987. The increase in speed limits was the result of the National Maximum Speed Law being repealed in that year, allowing states to set their own speed limits. Some states did choose to raise their speed limits, but not all 50 states implemented higher speed limits in 1987.
Local, state and Federal. Federal is the highest, but all of them have their own powers reserved to them. Ex: States can decide whether they'll allow gay marriage, speed limits, ect.
states
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.
Interstates and other main roads of the like which have the highest posted speed limits.
The highest speed limit for cars in the world is found on certain sections of the Autobahn in Germany, where there is no specific speed limit. However, in areas with speed limits, the maximum is generally around 130 km/h (81 mph). Other countries, like Italy, have speed limits up to 150 km/h (93 mph) on some highways. It's important to note that these limits can vary widely depending on the region and road conditions.
In the 1950s, speed limits in the United States varied widely by state and type of road. Most states had maximum speed limits ranging from 55 to 70 mph on highways, while local roads often had lower limits, typically between 25 and 35 mph. The introduction of the Interstate Highway System in 1956 led to higher speed limits on these roads, reflecting a growing emphasis on automobile travel. However, the absence of a national standard meant that limits were often inconsistent across different regions.
The average speed from New York to Washington DC is 43MPH which hasn't change in the last 25 years. That should give you a idea of the Interstate avg speeds. One must account for traffic, road condition, normal congestion in high traveled areas. If you mean the average speed limit, it's probably 65 MPH. In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits. About 30 states have limits of 70 MPH or higher. A few Western states have no speed limits on certain stretches of highway.
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.
In the United States their is no limit, but in other countries their are limits on speed and power.
Parts of the German Autobahn do not have posted speed limits.
That varies between states, who have jurisdiction to set speed limits in their respective state.