I've got a system in my current car (BMW M5) that uses a camera to read speed limit signs and puts the current speed limit on my heads-up display. It's a cool system, but it's not perfect. It frequently has problems in school zones where it sees the 25 MPH sign and displays that whether the "school zone" rules are currently in effect or not. I'd agree with most of the posters here that allege that speed limits are set by ass-covering bureaucrats with absolutely zero consideration to actual public safety. Slow zones in residential areas are fine - I don't even have to be told to drive between 20 and 25 MPH is a neighborhood with kids out and about. But the speed limits on major roads and highways are ... I would say "childish," but that would be an insult to children. We're living with generations of people who grew up playing video games, and our car's steering, breaks, suspension, steering, etc. are massively superior to what our parents had (or even what we had a decade ago). When speed limits are set too low people get bored and find other ways to distract themselves, which virtually all more dangerous than going faster.