Background: I often make the trip that we around here call “going over the hill”, which means taking Hwy 17 over the Santa Cruz mountains (17 is the route between San Jose and Santa Cruz in NorCal). It’s a winding highway about 8 miles on the north side and 6 miles on the south side*. It’s known for lots of accidents as it can be rather busy and, in the winter, slippery.
But here’s the thing. I comfortably drive ~10 mph faster if I’m driving uphill vs driving downhill. No matter which side of the hill, and I’ve driven this hundred of times. Is this some noted phenomenon? Seems rather weird to me, and the only explanation I can think of (going uphill, it’s much easier to de-accelerate) doesn’t seem to quite explain it because I don’t de-accelerate.
*As an aside, many people assume that it goes east/west, but Santa Cruz has the dubious honor of facing south towards the ocean-- something newcomers here learn when they go to check out their first sunset on the Pacific in Santa Cruz only to find that the sun sets over land from most vantage points.
I think you feel more in control because it is easier to decelerate and you can keep a more (and slightly wider) steady throttle. Downhill, you have to constantly adjust as gravity keeps adding speed.
Depending on how the road winds over the hills (and I haven’t looked), you could be on the outside of most of the curves going uphill both ways and on the inside of most of the curves going downhill.
IOW, perhaps on average the curves are larger radius going uphill. Or at least the tightest curves, the ones that most limit your speed, are wider radius in the uphill direction.
Had the road been built differently the opposite could be true. I don’t know how much that issue is designed into roads versus just happening. But the difference does exist on many mountain roads.
I think this gets closest to nailing it. An engineer once explained it to me adding things like “frame geometry” and “torque make higher speeds uphill possible” but 90% is the sense of control and risk the driver feels. We played around on the Giants Despair Hillclimb course (cars on a paved hill road) ages ago and no one could come close to matching their uphill times going down with many of us doubling our times.
I would think most of the explanation need not be more complex than the fact that your stopping distance is much greater on a downhill grade than on a level or uphill road, in some non-linearly increasing proportion to the gradient. Drivers are probably intuitively attuned to this fact – I know that I tend to be cautious going down steep hills even if there’s nothing immediately in front.
I hate that road - but luckily I don’t have to drive it very often. But I do the same thing, and also the same thing on 152, another reasonably narrow mountain road.
I think the narrowness must have something to do with it, since I pretty much drive the same speed going up the Grapevine as going down the Grapevine, which has four lanes in each direction. Since trucks are confined to the right two lanes, they are not something you need to maneuver around.
Many of the previous posts make a lot of sense if one is really talking about approaching his vehicle’s handling limits. If you enter a turn a bit too fast going uphill, you can scrub off speed and maintain control by simply lifting off of the throttle a little bit. Enter a bit too fast going downhill, however, and lifting or braking can be an eye-widening experience ending in the ditch. So, yes, it is easier to drive faster uphill.
But I have also noticed that lots of people drive faster up a hill than down the other side, and it has nothing to do with turns or nearing a car’s limits. I often see people braking on the way down a hill, slowing down to a speed that is slower than they then drive on the flat or uphill. They actually seem frightened by speeding up a little bit. I tend to let gravity increase my speed downhill and then coast back to my regular speed - for the fuel savings.
As others are saying, I take the downhills a little slower and more cautiously because of the longer stopping distance. This is somewhat different than what I saw in SoCal a lot, the drivers were much slower on the uphill side because they didn’t bother to pick up any speed approaching the hill. Going over the Santa Susannah pass at the far end of the valley there’d almost always be a line of cars in the right lane crawling up the hill because their speed had dropped down so much they couldn’t effectively accelerate.
If there are switchbacks, then when you are going uphill, you are turning away from the precipice, but when going downhill, you are turning toward it, which is a LOT more intimidating.
It’s highway 17 which is an odd number and odd-numbered highways in the U.S. run north-south and even-numbered highways run east-west. So, their assumptions are curious.
