Ground Slope Behind Curb

[dficker]

A 35 MPH street, over crossing a Freeway. 6" high curb, with a gutter plate. We are raising the bridge for clearance on the freeway and am looking to minimize grading on the overcrossing road for the raised profile. Most standards I see show the ground sloping towards the curb to some hinge point, then a 3:1 or so down to existing. Is it OK to slope the ground down away from the curb?...and what would be a maximum slope away from the curb?

Guardrail is a factor, and will be placed to protect the bridge abutments, but could be scaled back due to the low design speed. I am expecting the GR to be placed 5' off the curb

 

[gbam]

We have typically sloped away at a 2% slope to the hing (+-2' back of sidewalk) then down. The maximum cross slope would depend if there is sidewalk or not. I have seen a 4' @ 10:1 then down. Talk with your reviewers to get their feedback.

 

[ACtrafficengr]

Be careful w/ guiderail 5' off the curb. You say it's low speed, so it may be okay, but the old rule of thumb is guide rail should be < 1 foot or > 10 feet from the curb, else a vehicle may bounce off the curb and vault over the rail.

Alternatives are using 4-rail bridge rail, or placing the rail between the sidewalk and roadway (which complicates rail end section design)

Also, if the guiderail is 5' off the curb, the effective sidewalk width is 4.5' If the bridge is over 200' long, you will need a 5' by 5' wheelchair passing area, or you will need to justify it as a non-standard feature in accordance with the ADA regs. (Section 4.0.6, I think)

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