Banked off-ramps.

[King Friday]

Why can't highway engineers bank off-ramps or even bends in the highway that can't be taken a full speed? I'm not talking about Daytona 500 inclines, but maybe a few degrees to make the turn more manageable. Seems like it would help with rain water runoff too.

Is it that they can't do it, or they just won't do it.

[Hampshire]

I think most of them actually are banked. It's just not as drastic as you would think. Noticible banking would probably confuse most drivers since its very different from normal driving habits.
I think they also prefer people do slow down around corners for safety reasons.

[Shagnasty]

They do at least here in Massachusetts. Massachusetts traffic engineers could fuck up wet dreams for the entire population and simultaneously kill most of us through stupidity and negligence but that is one thing they do right. IIRC, most interstate highways have nicely designed exit ramps with the appropriate degree of tilt.

[King Friday]

Originally Posted by Hampshire

I think most of them actually are banked.

I'm going to have to pay closer attention on the off ramps, but there's one spot in particular on the Baltimore beltway that has you slowing to 40mph. Seems like a good spot for a bank. You're probably right about the off ramps though.

[Squink]

Originally Posted by Hampshire

I think most of them actually are banked. It's just not as drastic as you would think.

I think they intentionally underbank as well.
Ripping down I-80 through Iowa at 90mph many years ago, I noticed that there was no need to turn the steering wheel in curves.
Having that effect kick in at 60, or somewhere near the speed limit, could cause inattentive, pokey drivers to drift off the road in curves.

[Joey P]

They are in Wisconsin as well. The thing is you really don't notice it unless your at a standstill in traffic and you realize how tilted your car is.

[Ubertwizzler]

I think it varies a lot by state. Minnesota seems to be the worst. I've wondered whether it's because they want flat roads to make snow plowing easier.

[KneadToKnow]

Exit ramps by and large are pretty steeply banked 'round here, but then this is the home of NASCAR and all that.

[Spezza]

Majority of on/off ramps are banked around here (Southern Ontario). (Same as highways, all turns are banked to some degree.) The only incidences where I can think of un-banked, or not very banked, on/off ramps are in more rural areas. Head up north a few hours and the on/off ramps there are short and tight. I suspect this is because they were built a few decades ago when certain highway requirements weren't in place. I went up north at the end of last summer and in areas where new highways are in place each controlled access entrance/exit was designed like "normal". Only old highway segments had the short tight exits.

[GorillaMan]

Originally Posted by Ubertwizzler

I think it varies a lot by state. Minnesota seems to be the worst. I've wondered whether it's because they want flat roads to make snow plowing easier.

Or to prevent snow drifts blocking the road in the first place? A banked curve strikes me as the perfect snow-catcher, if the wind happened to be in the right direction.

[Joey P]

Originally Posted by GorillaMan

Or to prevent snow drifts blocking the road in the first place? A banked curve strikes me as the perfect snow-catcher, if the wind happened to be in the right direction.

I've never noticed drifts on banked curves, but I do think an icy off ramp that wasn't banked would have a lot of cars in it's ditch.

[NinetyWt]

In design it's referred to as "super elevation". Here's a link to an explanation which has a nice little animation. Highway design in the U.S. is supposed to conform to AASHTO's Design guide. As Spezza pointed out, design standards change over time and it is possible that some ramps which you have encountered are old and not up to current standards. Heres' another article about geometric design and super elevation.

[Mangetout]

They have to make them possible to use when traffic is slow or at a standstill. Also, if they made them significantly banked, some less experienced and less confident drivers might find them dangerously intimidating.

[butler1850]

One thing to keep in mind is that roads are not always used at the speed they are designed for. This works in both the faster and slower direction.

Here in NH, heading south on the Everett Turnpike (Manchester to Nashua), just south of the Bedford tolls, there is a section of road under the power lines that has a pretty good bank to it. It's great on a dry day, at normal speed. You barely have to turn the wheel. Pure, smooth travel.

On a snowy day, when traffic is down to about 20mph on that stretch, with the right kind of snow, you simply aren't going fast enough to keep up on the banking. I've nearly gone sliding down the hill, while still moving forward. I've seen folks go off, and so many 'close calls' to catalog properly. You are simply driving normally, then you are sliding down hill to the right. You need to think quickly, and angle yourself uphill, but of course, now you're pointing towards the outside lane, in which other drivers are having the same problem, and sliding TOWARDS YOU!!!

For what it's worth, during the Budweiser Shootout last Saturday night, Bill Elliot in the #21 Air Force car stopped on the top of the banking, against the wall, right in the middle of the turn. The tow trucks can't go there, and stop, or they will tip over. The #21 can be seen sliding it's front end sideways (NO forward motion. Engine off, in gear) as it sits on the track. The tires were oriented perpendicular to the direction of the banking, and simply slid straight down in short little bursts until they finally got enough traction to stop. The track workers needed to attach a cable, and drag it down out of the banking to hook it up to the wrecker. Those turns work great at 180+mph (need to repave though to get rid of some of those bumps), but are pretty scary when you stop.

[Hampshire]

In addition to banked turns in higway design there is typically always some type of slope in the design. Standing water on a freeway can be disasterous with vehicles hyroplaning at 60mph. Typical straight away highways are crowned so water always runs immediately off.

[NinetyWt]

Originally Posted by Hampshire

Typical straight away highways are crowned so water always runs immediately off.

That crowned section can be seen as the "Normal Section" in my first link.

[tremorviolet]

Originally Posted by NinetyWt

In design it's referred to as "super elevation". Here's a link to an explanation which has a nice little animation. Highway design in the U.S. is supposed to conform to AASHTO's Design guide. As Spezza pointed out, design standards change over time and it is possible that some ramps which you have encountered are old and not up to current standards. Heres' another article about geometric design and super elevation.

Well, shoot, this is every point I was going to make. You're more often gonna see overly tight or short ramps in urban areas where there wasn't much room to begin with plus the highways were probably built years ago when design standards were different. Even with changing design standards, the DOTs don't have the money to rebuild exits unless there's an obvious danger or insufficiancy.