Unlike speed bumps which force a driver to slow down considerably to avoid damaging their car, speed humps let vehicles pass at a considerably higher speed and with less discomfort for the passengers. They are roughly 4 to 5 feet in width as opposed to about 1 foot for a speed bump. They also have about the same height as a speed bump. One would probably have to hit a speed hump at about 70 km/h to do any serious damage.
Speed humps have recently been placed on several residential streets in my area that are frequently used by people taking a back way to the local grocery store. While the speed humps have certainly slowed traffic on these streets, there is still roughly the same volume of traffic due to the congestion on the main roads.
The speed humps in my area were accompanied by signs falsely designating the area a "traffic calming zone". Two signs were also posted next to each speed hump, one saying "speed hump" and the other with a picture that one might expect to see on a UFO Landing Site sign. The "speed hump" signs have all disappeared however, most likely taken by teenage boys.