kyser_soze said:
you can only damage your undertray/suspension on a speed bump if you hit it at speed or are grossly overloaded and try taking them too quickly (i.e as the driver you should have adjusted your speed to take account of the extra load)
Not necessarily true. Depending on a combination of the design of the hump and the vehicle, damage can occur at speeds well below the applicable speed limit, especially if you're passing over them regularly.
Implementation of humps can vary wildly. There's an example of a raised junction in Merton that I used to encounter on my cycle route to work which had a 5cm vertical concrete step at its edge, right across the road. On a touring bike, the only option was to stop and mount it like a pavement kerb. I doubt it was doing cars that passed over it any favours, whatever speed they were doing.
Browsing through the 2004 London Assembly Report,
London's got the hump (263KB PDF) there are mentions of representations about damage to vehicles from the Fire, Police, and Ambulance services, together with bus operators. I remember a story a few years back where the LAS had to send all 2,000 of its ambulances back for repairs and modifications that was ascribed to damage by speed humps.
The TfL response is that "damage should not happen to vehicles driving over speed humps if they travel at an appropriate speed i.e less than 20mph".
However, while observing the proper behaviour of matching one's speed appropriately for the conditions, the
Highway Code makes no mention of TfL's recommended speed in its notes on traffic calming and speed humps.
Since many speed humps are located on roads with 30 mph limits, and I can think of quite a few examples where these are relatively major routes, drivers may have reasonable expectations that they ought to be able to pass over them safely at 30 (as Ed pointed out earlier, the humps are there to reinforce existing speed limits, presumably).
If 20 mph is the recommended speed for negotiating humps, I do believe that message ought to be communicated to the public a bit better.
Lastly, the design of some humps can be such that, with some cars, it's actually
more comfortable to pass over them at over 20mph. It's all a bit of a lottery.
With some decent design and appropriate siting, speed humps are OK. The biggest problems I have with them is that they often fall below those standards.