Limitations of Road Gradients

I recently saw a flat bed articulated lorry grounded such that it lost traction at an intersection on a slope. The guy had to unload the fork lift truck from the back and mess about trying to get the drive wheels to both touch the road (you think they'd have a lockable differential to help in these situations)
So I'd do some arithmetic based on wheelbase and ground clearance.
Del

I had a similar experience on a country road north of Newcomerstown, OH. But it is more a change in gradient than the amount of gradient. My road was more-or-less level; the cross road was downhill both left and right. The semi (road repair crew) wanted to come up from the left and turn to his left, but the drive wheels were lifted off the road. At least he could back up. He ended up going straight across (without turning), but the landing gear dragged a lot.

I left my heart in San Francisco...one of the world's road gradient capitals....

They seem to make their intersections pretty close to 0°; the effects can be seen in the movie Bullitt, for instance. Or just go there and drive around.

It depends upon the intended usage of the Road, responsible agencies and applicable regulations. For instance, most State Highways funded by FHWA can not exceed a 6 % grade. However, I have seen residential roads up to a 15% grade, which is about the maximum that a smooth drum roller can climb whiles in vibratory mode. The intersections tend to be flatter, but I have seen these even upto 6% where both roads crosses on a hillside at a acute angle upslope. The other consideration is whether there will be a stop, you can not expect people to stop in the same distance on steep downgrades, and it can be problematic for them to start fom a stop bar on steep upgrades. Also steep grades become a problem for standard roadwork equipment, which must be considered in construction and O&M. You should check the FHWA website for reference information, and possibly CalTrans since they do a majority of the US research which other states utilize.

I seen this poor lady stuck on Divisadero St.(25% grade) in San Francisco, while driving up hill, in a new Subaru Impreza WXR that has "hill hold" and was to scared to move!! She had traffic backed up for over 8 blocks! I don''t know what happen to her, as I was on the down hill side and I couldn't stop.

In my experience, the roadway that is considered the thoroughfare, or the artery, maintains its crown, typically 2%, as if there were no intersection. The intersecting street, regardless of profile grade should have the same 2% along its profile for a distance of preferrably 50' from the main road and then a vertical curve up or down if its profile is not already at that gradient.

Admittedly, there are circumstances where that detail is not practical, but it certainly is the appropriate way to design intersecting roadway profiles because it eliminates the abrupt dip at the edge of the main road and it improves starting from a stop on the side street to enter the main street. I have certainly been on many streets here in the west where there is such an abrupt channel at the edge of the main street that, if you are crossing it with the right of way, you have to damn near stop to keep from bottoming out or going airborne. I understand that it is there because there is often no sub-surface storm water drainage system on account of the cost versus the infrequency of rain events. When rain events do occur, they are often what are referred to as 'monsoons' on account of their intensity and, when they occur, the local topography is such that most of the runoff would pass the inlets anyway.

I have to agree with Doogleas. We typically do our best to meet his same standards.

If there are sidewalks and/or mass transit in the area, You also have to be careful about meeting ADA regulations as much as possible. They've really been strict on meeting ADA regulations around here lately.

They have gotten to the point of actually going out and checking the slopes of the sidewalk ramps and cross slopes at the cross walks. If they don't meet minimum they make the contractor tear it out and rebuild it.

We've gotten in the habit of designing all ADA stuff with and extra 1/2% slope taken out to give the contractor some leeway when he builds it.

I think the probability of snow and ice will be significant.

Have driven over this road a few times. Not for the faint hearted. But funny to see a driver thinking he could get a bus over it.

http://www.visitcumbria.com/wc/hardknott-pass.htm