Your original post was time only. I went back and checked.

I'm the dick that took it down the path of what your odds of getting caught speeding were and how much it would cost you in terms of time.
It does make more sense to evaluate the issue in economic terms. You could solve it as an optimization problem for the ideal amount to speed/not speed.
You'd need the following information as a starting point:
Odds of getting caught speeding as a function of speed in excess of the limit
Cost of speeding infraction for the ranges of speeding
Odds of being in accident as a function of speed
Average cost of repairs/court costs/etc. for being involved in an accident as a function of speed
Average fuel cost as a function of speed
Some sort of economic value you assign to your time
You could estimate how many miles you drive per year on the highway and in residential areas and calculate based on zone type. Or you could subdivide the problem further: 25 mph zones, 35 mph zones, etc.
I bet I could turn this problem into a master's thesis at least, maybe a doctoral thesis.