December 26


The New Speed Hump Alternative

By Mike Spack

December 26, 2012

Speed Kidney Traffic Calming

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 – for more information (although google didn’t do a good translation job for me).



  • The device was not tested under snow conditions because it does not snow during winter on the locations.
    However, the beginning of the main speed kidney is not perpendicular to the roadway. So, we think that the shovel would not impact with the device, it would slide along the entrance ramp and then go over the speed kidney without difficulties.
    What do you think?

  • Ana – It would be physically possible to plow out the speed kidney, but it would be time consuming. The typical large street snow plows would be able to go over the top, but they’d need to lift their blades up. That’s unpleasant for the driver working at 3 in the morning. They want to just drive the streets and get the job done. BUT a smaller plow would need to come back letter to plow out the middle of the kidney between the islands. Otherwise ice would build up in the kidney and present unsafe conditions. This would be time consuming. Speed humps, chicanes, bumpouts, etc all present plowing problems. The speed kidney also would fall into that category – it adds complexity for the plow drivers.

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    Mike Spack

    My mission is to help traffic engineers, transportation planners, and other transportation professionals improve our world.

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