I got into RD's not because I want to speed with impunity but because I felt that oppressive policing of the limit was more associated with revenue gathering and to give the impression of doing something about the road toll rather than actually addressing the more complex issues involved in road safety.
Here's a very informative UK site that explores these issues :-
One of the latest pieces of research to look at crash/near miss causes was done in the US and probably has implications for the driver/RD interface.
Crash Test Dummies
To my mind it looks pretty much that anything that distracts you from the central task of what's going on "out front" carries with it the possibility that it's going to happen at just the wrong moment in time and cost you dearly. Some of them can't really be avoided; checking mirrors, blindspot, speed etc. are simply part of the job. It's the optional extras like the stereo, mobile phone, Sat Nav, CB radio and of course the RD that are more of a worry. It's not so much that you are going to be the prime cause of an accident while operating these pieces of equipment, more that your response to a problem is going to be delayed by a few crucial seconds.
So how should a RD function if it's not going to pull your attention away from what's important?
Answers on a post card to "That's the $64000 question smartarse, The End Of The World, SW Pacific"
My thoughts are:-
You shouldn't have to look at it, it should tell you what you need to know audibly, alert, band id, self mute and then a rising tone as the threat approaches. You shouldn't have to touch it pretty much from journeys start to end and you shouldn't be spending time trying to decide if an alerts real or where it is. A HUD would be cool too 8)
What would be on your wishlist?