Seconds count. We already know that speed bumps kill 9 for every 1 life they save, due to ambulance delays. Ambulances are heavy and can't go over speed bumps very quickly. The 1 life they save is from someone not going so fast.
I'd be very surprised if that was actually a rigorously proven stat.
http://www.edmecka.com/Forms/tfc_calm.pdf
Oh, on page 158 they claim it is more like 40 lives lost per 1 life saved in Austin, TX.
I'm in SoCal and some of these neighborhoods are just full of speed bumps, so maybe it's all of those seconds adding to minutes? Also there are different types of speed bumps, some don't slow you down at all and others you go 5mph and feel like you're ruining your suspension. Or maybe there's some other confounding factor? Do you only have a few where you live?