Examples of banked curves on public roads?

[davewiecking]

Are banked curves used anywhere to allow high speed turns on public roads?

DC Beltway east of Rockville Pike. Aka the Rock Creek Rollercoaster. Recall a Driver's Ed teacher (1973) saying it had the largest such banks on the interstate system, and in icy weather cars could slide sideways. Not saying that's true, but...

[Scott5114]

Maybe the next technical breakthrough would be a road that senses the speed of the vehicles on it, and increases or decreases the banking of the road to compensate. That way the 150 mph cars could keep going strong, yet grandma on the way to bingo could putter along at her pace.

(where's that sarcasm emoji?)

And if it detects a car without a license plate, it banks up super fast and tosses the car clear into the next county!

[hotdogPi]

Maybe the next technical breakthrough would be a road that senses the speed of the vehicles on it, and increases or decreases the banking of the road to compensate. That way the 150 mph cars could keep going strong, yet grandma on the way to bingo could putter along at her pace.

(where's that sarcasm emoji?)

And if it detects a car without a license plate, it banks up super fast and tosses the car clear into the next county!

Or a "low polygon count pickup truck", for that matter.

[Dirt Roads]

But I mean wouldn't a Nascar style curve allow for higher speeds with a smaller turning radius?

Great question.  This is a three dimensional puzzle that confounds the civil engineers when designing high-speed railroad trackage (and similar other technologies).  The simple concept is that the centerline of the [lane] needs to be rotated at a constant rate (called "roll rate") until the design superelevation is achieved.  In theory, you want the entire section of tight curve radius to be set at the design superelevation, but the spiral rate into the curve radius seldom can be coordinated with the roll rate, which at some point also needs to be spiraled.  This is where it gets tricky, as the design line needs to split from the centerline to both the top-of-curve and the bottom-of-curve (each with their own curve designs).

On railroads, the spiralling of superelevation is simple because we are stuck with crossties that are straight and flat.  On rubber-tired trains, the guideway design gets tricky because there is a tendency to "scoop out" the centerline (which is exactly what you see on a NASCAR track).  Since we calculate the G-forces on passengers (hence the maximum curve speed) based on the characteristics of the centerline [of each lane], calculating the effective superelevation versus curve radius when you are "rolling" and/or "spiralling" into both the curve radius and the banking is a mathematical problem that is not for the timid.  And this is often more important to establishing the "maximum safe speed" than when in the peak of the banked curve.

Worse, unlike NASCAR we railroaders and highway guys also have to address changes in vertical curves.  When I've been on the design teams, I won't let the designers play with both horizontal and vertical curves at the same time so we won't mess up the "maximum safe speed" calculations.

[vdeane]

But he's also probably missing the connection that a banked curve on a NASCAR oval is designed for 150 mph speeds.

It's K12.  That's probably why he wants them - for the 150 mph AI cars.

[hbelkins]

There was a pretty funky banked curve on the Mountain Parkway just east of Exit 53 (the KY 1010/Hazel Green exit) that got reworked during a recent pavement rehab project, then completely obliterated as the widening project continues.

[kphoger]

But I mean wouldn't a Nascar style curve allow for higher speeds with a smaller turning radius?

I once drove an unpaved road that had a pretty good banked curve, shortly after a heavy rainfall.  My car slid down the mud to the bottom, and I was barely able to get back up and turn around.

So yes, steeply banked curves would allow for higher speeds with a smaller turning radius.  But only in good conditions.  You'd better hope to God you don't find yourself driving slowly around such a curve on icy roads, or else you're going to be stuck for a while.

I'm sure half of us on this forum could describe a time when our vehicle started to slide on ice while standing still at a complete stop.

[Dirt Roads]

But I mean wouldn't a Nascar style curve allow for higher speeds with a smaller turning radius?

I once drove an unpaved road that had a pretty good banked curve, shortly after a heavy rainfall.  My car slid down the mud to the bottom, and I was barely able to get back up and turn around.

So yes, steeply banked curves would allow for higher speeds with a smaller turning radius.  But only in good conditions.  You'd better hope to God you don't find yourself driving slowly around such a curve on icy roads, or else you're going to be stuck for a while.

Not only the issue with sliding down a steep bankment, but there is also the possibility of rollover for high loads that have a very high center-of-gravity.  Many railroads increased Amtrak speeds by increasing the superelevation to 6 inches (as measured from top of the high rail -to- top of low rail, which is over 10.6%).  But back then, there was an immediate problem with tall grain railcars flipping over down towards the inside of the curves.  So-called "grain trains" were therefore required not to operate between 11 MPH and 17 MPH.

(My understanding is that these situations are no longer considered acceptable, and presumably the superelevation is no longer allowed to be set at 6 inches when such conditions might occur).

I'm sure half of us on this forum could describe a time when our vehicle started to slide on ice while standing still at a complete stop.

Some of us have done while standing still (and not in a vehicle).  I've slid down a banked curve more than once, and also had the misfortune of getting out of a car only to lose grip of the door handle, thus sliding down the parking lot more than 200 feet (somehow, I never did fall). 

[kphoger]

Many railroads increased Amtrak speeds by increasing the superelevation to 6 inches (as measured from top of the high rail -to- top of low rail, which is over 10.6%).  But back then, there was an immediate problem with tall grain railcars flipping over down towards the inside of the curves.  So-called "grain trains" were therefore required not to operate between 11 MPH and 17 MPH.

TIL grain hoppers come in different heights.  At first, I thought you might be talking about woodchip gondolas or something, but then I realized "grain trains" most likely referred to unit trains made up of those smooth-sided covered hoppers that are favored for freight-hopping because of the likely presence of a "porch" and covered "cubby" (or, I suppose, there are also unit trains of uncovered hoppers too).

[dlsterner]

Maybe the next technical breakthrough would be a road that senses the speed of the vehicles on it, and increases or decreases the banking of the road to compensate. That way the 150 mph cars could keep going strong, yet grandma on the way to bingo could putter along at her pace.

(where's that sarcasm emoji?)

And if it detects a car without a license plate, it banks up super fast and tosses the car clear into the next county!

Why not helicopters with giant magnets and ... err, never mind ...

[freebrickproductions]

Many railroads increased Amtrak speeds by increasing the superelevation to 6 inches (as measured from top of the high rail -to- top of low rail, which is over 10.6%).  But back then, there was an immediate problem with tall grain railcars flipping over down towards the inside of the curves.  So-called "grain trains" were therefore required not to operate between 11 MPH and 17 MPH.

TIL grain hoppers come in different heights.  At first, I thought you might be talking about woodchip gondolas or something, but then I realized "grain trains" most likely referred to unit trains made up of those smooth-sided covered hoppers that are favored for freight-hopping because of the likely presence of a "porch" and covered "cubby" (or, I suppose, there are also unit trains of uncovered hoppers too).

I could also see it potentially being an issue with double-stacked intermodal containers as well.

NS 8098 - NS 288 - Stevenson, AL by freebrickproductions, on Flickr

[kernals12]

But I mean wouldn't a Nascar style curve allow for higher speeds with a smaller turning radius?

Higher superelevation = more dirt work = more expensive

But less land overall

[Scott5114]

But I mean wouldn't a Nascar style curve allow for higher speeds with a smaller turning radius?

Higher superelevation = more dirt work = more expensive

But less land overall

Labor is more expensive than real estate.

[RobbieL2415]

Banked curves on freeways are very common.

Here is a modern example of a banked curve on an off-ramp, with a design speed of 65mph. Note that the right parapet of the bridge is pitched slightly higher than the left.

https://maps.app.goo.gl/uv76GhwgyQTxDgT2A?g_st=ac

Later on, after merging onto the Interstate from said on-ramp, is this banked curve, build circa 1985.
https://maps.app.goo.gl/hvzjEa2xjC724hEf7?g_st=ac

[thspfc]

CTH-CV in Madison

https://www.google.com/maps/@43.1685478,-89.3335325,3a,25.2y,267.19h,88.33t/data=!3m7!1e1!3m5!1sD9Jmi1CJhz0nUshHpqKfpg!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D1.6689949824381216%26panoid%3DD9Jmi1CJhz0nUshHpqKfpg%26yaw%3D267.1915075730727!7i16384!8i8192?entry=ttu&g_ep=EgoyMDI1MDIyNi4xIKXMDSoJLDEwMjExNDUzSAFQAw%3D%3D