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Updating Roadside Design Practices

State KS
Description Text

KDOT is working on updating our Roadside Design Practices document. One item that has come up in our discussions is when we would recommend evaluating whether or not to shield a culvert located at or beyond the clearzone.

Currently our guidance states if the culvert has a height greater than 8 feet then it is recommended to conduct an engineering study, which may involve using RSAP, to evaluate whether the culvert should be shielded regardless of whether or not it's located at or beyond the clearzone. I know the 8 foot height selected previously was based on the anticipated crash severity of an accident involving a vehicle dropping greater than 8 feet being greater than the severity of accidents where the vertical drop is less than or equal to 8 feet, but I haven't been able to find any research to support the 8 foot height selection.

Are you aware of any research that may have information regarding anticipated crash severity relative to vertical drops? I've read through the RDG and a few studies MwRSF has completed in the past (e.g. Evaluation of Safety Treatments for Roadside Culverts), but didn't find anything that addressed or provided some type of Severity Index directly related to vertical drop.

Any information you, or someone at MwRSF, can provide would be greatly appreciated.


Tom Rhoads


  • End Treatments & Crash Cushions
  • Traversable Features
Other Keywords Culvert, Vertical Drop, Dropoff
Date July 25, 2017

Response We are not aware of any research that specifically defines the severity of vertical drops. 

We did look at cost effective treatments for low-volume roads which included analysis of culverts with various heights. 


Date August 11, 2017

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