Problem drainage on a very steep street 3

[Boltricity]

I've been asked to look at some drainage problems on an existing fairly long and steep street (10% grade). It was designed with a 2% crown. It is a heavily traveled street with two or three lanes in each direction.

The issue is that during heavy rains there is a lot of water on the pavement which causes vehicle spinouts. Much, if not most, of the water is not getting over to the curb and gutter (and thus the drainage inlets) but instead is “sheet flowing” down the road. This is not surprising when you look at how the pavement is contoured. (A 10% longitudinal slope vs. 2% cross-slope results in contours running almost perpendicular to the road alignment). It's almost as if there was no pavement cross-slope at all.

Does anyone have any experience dealing with something like this, either in the original design or to remediate an existing problem? Obviously in a new design, one could increase the 2% cross-slope some. Too late for that here, unless a complete overlay is done. And since there is an existing raised median, the median would probably have to be torn out and raised.

Someone has suggested installing trench drains in the pavement, but I'm not sure they would be that effective.

Thanks for any suggestions provided.

 

[beej67]

I can't emphasize enough how well open graded friction course top coats work down in this area of the country to advect water to the sides of the pavement through the center of the pavement section instead of along the surface. They're really quite amazing.



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