eli5: How do they decide what the speed limit is for a road?

Question

Basically the title. I’m curious what they do to decide. surely they don’t just stick a random number on a sign and call it a day.

In: 16

Answer 1

It probably varies by country but at least in Portugal (and the whole EU?) there are speed limits defined by type of road. Within cities/villages = 50, Outside = 90, Highways 120. Then, based on specificities of roads they may set lower speeds. For example, next to schools = 30, roads where pedestrians are forbidden = 80, zones prone to accidents = 20 less than normal.