acceptable road gradients

[swazimatt]

I have a client who would like to build his house on a site with a very steep access. Looking at the topo-cadastral map the only possible route has a gradient in the region of about 1:3.5 Is this too steep for a driveway? the length of this section would be about 100m

 

[Debaser]

The steepest gradient I usually see quoted in guidance is 1:8 (12.5%). A 1:3.5 slope (i.e. a 28.5m rise over the 100m) is way too steep unless the owner has a Hummer, or a winch and steel cable located at the top of the slope. We (UK) usually reserve that sort of batter for embankment slopes.


(I assume from your ID that you are in Southern Africa/Swaziland so I don't suppose you'd otherwise have too much of a problem with ice/snow).

 

[swazimatt]

thanks Debaser, we also work on the same gradients, but that is for public roads, was wondering if it could go steeper for a driveway.

Yep, in Swaziland, so no ice or snow

 

[Debaser]

I can't say it's not been done;

http://en.wikipedia.org/wiki/Hardknott_Pass

but you'd certainly need some sort of flatter area (1:5 say) where the private road joins the public highway (and where nervous drivers can stop and let their brakes cool).

I can't see you getting any sort of service vehicles up there either (do you have tracked refuse lorries?), never mind constructing the thing (e.g. laying bitmac at 1:3).

 

[Debaser]

Sorry, that should have read '...some flatter area (1:20 say)...' I'm mixing up my 1:X with my Y%'s.

 

[francesca]

Swaziland does have heavy rain, though. You'll need to do some serious drainage engineering to prevent the driveway turning into a donga. You also need to make sure that a nice summer thunder storm doesn't send a vehicle sliding off the side. I thought Swaziland and Mpumalanga were rolling hills.