Japan: R= curve signs

[mcmc]

Saw these signs all over the mountain expressways in the south of Kyushu. What the heck does R=###m mean?

[westerninterloper]

I believe it is "radius", the length of the curve.

[Rothman]

I believe it is "radius", the length of the curve.

Radius isn't the length of the curve.

[CtrlAltDel]

I believe it is "radius", the length of the curve.

Not so much the length of the curve, but the curve's sharpness. The smaller the number, the tighter the curve.

[Rothman]

I believe it is "radius", the length of the curve.

Not so much the length of the curve, but the curve's sharpness. The smaller the number, the tighter the curve.

That's more like it.

[mcmc]

Still doesn't completely compute to me. In simple English, what message is "R=500m" trying to convey?

[CtrlAltDel]

The radius of a circle, or arc thereof, is the distance from that circle to its center. A smaller arc curves more sharply than a larger one. Thus, the blue curve is gentler and easier to negotiate than the green one. "R=500m" means a curve with a radius of 500 meters, which is on the lower side of acceptable curvatures for a high-speed route.

[kurumi]

Below is "速度注意" -- pay attention to your speed. The context is definitely "sharp curve, don't take it too fast".

[mcmc]

Thanks for the graphic, CtrlAltDel!

I'm proof that this sign wouldn't fly in the U.S.

[formulanone]

There's a famous curve at Suzuka Circuit named 130R; it's taken nearly flat-out by drivers.



Now I know how it got its name...

[CtrlAltDel]

it's taken nearly flat-out by drivers.

Now it's my turn to plead ignorance. What does it mean to take a curve flat-out?

[formulanone]

it's taken nearly flat-out by drivers.

Now it's my turn to plead ignorance. What does it mean to take a curve flat-out?

Flat-out: driving through a corner without slowing down or downshifting.

Technically, it's not too unusual for most our our daily driving at an average of 55-70 miles an hour, but much less so for a sharp turn at 150-180 mph.

[Scott5114]

This seems like it's basically doing the same thing as advisory speed plaques in the US do, but assuming that the driver has enough experience with their particular vehicle to determine a safe speed through a curve of a given radius. Neat idea, but I'm not sure it would work too well in the US.

[Road Hog]

I'm sure state DOT engineers take curve radii into consideration as well as type of pavement and banking when they assign maximum safe speeds to a curve here.

[Rothman]

I'm sure state DOT engineers take curve radii into consideration as well as type of pavement and banking when they assign maximum safe speeds to a curve here.

This is true.  At least when I interned wifh FHWA's Office of Safety, I assisted with revising such recommendations.

[kalvado]

I'm sure state DOT engineers take curve radii into consideration as well as type of pavement and banking when they assign maximum safe speeds to a curve here.

This is true.  At least when I interned wifh FHWA's Office of Safety, I assisted with revising such recommendations.

Ine of limitations here is that,  for a tight radius urban highway, there are 4 advisory limits to choose from - 55,50, 45, maybe 40. 35-30-25 for ramps are ok. Oh, it must be safe for a 18 wheeler, right?
Radius info relays not limitation - which can easily be capricious - but underlying reality to consider. While ommitting details about other factors, driver experience of other posted curve easily tells how serious the message is.

[Scott5114]

The problem with a curve warning speed is that it doesn't take different vehicle types into consideration. A safe speed on a curve is going to be different for a heavily-loaded semi versus a sedan.

[kalvado]

The problem with a curve warning speed is that it doesn't take different vehicle types into consideration. A safe speed on a curve is going to be different for a heavily-loaded semi versus a sedan.

A counterargument would be speed difference is an issue,  and sedan breaking in a curve because a semi in front cannot go to fast is a real problem

[Scott5114]

True. But on the other hand... calculating a curve warning speed means you have to pick some type of vehicle as being representative of the average vehicle driving on the road. What the most representative vehicle is, and what its capabilities are, will change over time. I think I remember reading that in some states the formulas for calculating curve speeds were drawn up in the 1960s, before power steering existed, and have never been updated.

The upshot of this is, in my experience, curve warning speeds are so hilariously out of step with my car's capabilities that I basically ignore them unless they have an alarmingly low number like 15 (and even then, a sharp-turn sign is bound to accompany them and be just as much of an indicator to slow down).

[Alps]

True. But on the other hand... calculating a curve warning speed means you have to pick some type of vehicle as being representative of the average vehicle driving on the road. What the most representative vehicle is, and what its capabilities are, will change over time. I think I remember reading that in some states the formulas for calculating curve speeds were drawn up in the 1960s, before power steering existed, and have never been updated.

The upshot of this is, in my experience, curve warning speeds are so hilariously out of step with my car's capabilities that I basically ignore them unless they have an alarmingly low number like 15 (and even then, a sharp-turn sign is bound to accompany them and be just as much of an indicator to slow down).

Depends on the state in the USA. Some states like PA ludicrously underpost and can be ignored. Some like TN really do need to be heeded.

[formulanone]

True. But on the other hand... calculating a curve warning speed means you have to pick some type of vehicle as being representative of the average vehicle driving on the road. What the most representative vehicle is, and what its capabilities are, will change over time. I think I remember reading that in some states the formulas for calculating curve speeds were drawn up in the 1960s, before power steering existed, and have never been updated.

The upshot of this is, in my experience, curve warning speeds are so hilariously out of step with my car's capabilities that I basically ignore them unless they have an alarmingly low number like 15 (and even then, a sharp-turn sign is bound to accompany them and be just as much of an indicator to slow down).

Depends on the state in the USA. Some states like PA ludicrously underpost and can be ignored. Some like TN really do need to be heeded.

I've noticed that some places just suggest a speed 5-10-15-20-etc miles an hour lower than the posted Speed Limit sign, which it a pretty good indicator of how sharp the curve is. So the amount of preparation for braking or downshifting can be calculated in kind...but there's also many routes that do not bother with suggested speed limits, let alone posting (or re-posting) curve warning signs.

[skluth]

This seems like it's basically doing the same thing as advisory speed plaques in the US do, but assuming that the driver has enough experience with their particular vehicle to determine a safe speed through a curve of a given radius. Neat idea, but I'm not sure it would work too well in the US.

There would be learning curve for motorists, but I can see this being more useful than the generic American "Slow Down Sharp Curve Ahead" sign. Often there's an additional sign with a recommended max speed in the US but that's not as informational.