Introducing the speed kidney (the industry may need to work on the name)! Garcia, Moreno, and Romero have a good article in the December 2012 ITE Journal about this new traffic calming device they’ve developed. Below is a snaphot from the article that shows diagrams and design parameters.
In essence, they’ve designed a chicane into a speed table. A raised comma shaped hump is put in the middle of each driving lane and a raised oval is put on the centerline of the road. So either the driver keeps driving straight and hits the comma/oval and it acts like a speed table/hump or they turn so the car drives over the comma and it acts like a chicane.
This seems to be an ingenuous combination of ideas. Either way, it slows down traffic. It also allows emergency vehicles to have a smooth ride (a big negative comment of speed humps is ambulances/fire trucks going over them).
The authors have done a lot of test track evaluation and built one of these on a street in Spain. The initial results are promising with average speeds going down 3 mph. They didn’t discuss if the speed kidney lowered the speeds of the “outliers”, which I think is the most important task of traffic calming – getting the excessive speeders to slow down. There’s also no mention of snow removal, which could be challenging (which us Minnesotans have to think about).
I think agencies should start testing out the speed kidney. It seems to be an innovative idea that combines the two most effective traffic calming strategies while reducing some of their negatives. Check out the authors website – www.SpeedKidney.com for more information (although google didn’t do a good translation job for me).