Portland, OR, has gone very heavily into traffic calming measures on residential side streets -- particularly ones that served as informal shortcuts to arterial streets. This means speed humps, as well as traffic circles and street narrowing. They claim that they shape they use doesn't slow down emergency vehicles, but I haven't read any recent studies.

Of course, at least Portland tries -- they've research shapes, the profiles are quite consistent, and they are very well marked, lots of paint and signs as you approach each one.

Here in Rhode Island, as usual for the incompetents here, they've started putting speed humps in Providence neighbhorhoods but in a crappy way. Instead of a rounded profile, their "humps" often consist of a slab of asphalt about 2' long and 4" thick, with edges that come up from the road at a 45 deg or steeper angle. No paint at all, and often the only signage is a single sign at the beginning of the block saying "speed humps". If they remembered to put it up at all.

So, driving down such a street, especially at night, you basically slam into 4" ledges with no warning.

But that's typical here. Last year they redid a major downtown intersection, two blocks from city hall. They painted the crosswalk on one side of the intersection.... and installed the "walk / don't walk" signal on the _other_ side. Still hasn't been fixed.