This one was placed in front of a school house, so I'm guessing they installed the traffic calming device on this bike-only path to decrease the pedestrian/bicycle crashes.
The collisions between children and all kinds of traffic--including bicycles--has steadily improved in the Netherlands.
"Over the past decades, road safety has improved more for children than for the rest of the population. In the mid-1980s, the number of fatalities among children was approximately 120 and in recent years it has been approximately 35."
(source: SWOV Fact sheet © SWOV, Leidschendam, the Netherlands, February 2009)
Horray for the bicycle speed bumps! Not only are they increasing the safety of school children, they are actually kind of fun to ride. Unlike car speed bumps, the bike bumps have a wavering bump that feels a bit like a roller coaster. Safety and fun for the price of one.