It tells you how fast you can drive on the road.
From the Nebraska state line, it's 75 until you get into the Denver metro area. Then it fluctuates between 55 and 65.
It depends on local legislation. Many countries have no restrictions others impose arbitrary rules.
When another speed limit sign is reached that changes the limit from the previously posted one.
Unmarked residential areas in Georgia have a speed limit of 25 miles per hour unless noted different by signage.
too many crashes . When I was young, there was only the 30mph limit in towns, and a few 40mph limits on urban through ways. Apart from that, no limit on the open road. Now we have 70mph on motorways...