Smart thinking?

Drove to a nearby town the other day. Thanks to roadworks (and there don't half seem a lot of them around lately), was forced to take a diversion down roads which all had speed humps. What a pain! The justification for speed humps seems to be to discourage people from using these roads as "rat-runs", and the council appear ever more willing to install them. But what they never seem to ask themselves is - why do people need rat-runs? The answer of course is that the main roads are just not up to the job - but rather than address that problem, it's easier and cheaper to install speed humps. Of course, by so doing, they exacerbate the problem on the main roads - now there's clever!