Turning Judgement

I don't think, I know. Most experienced drivers will tell you the same thing. It's no different than you knowing the ability of you car. With experience you know the vehicle's ability. In tight situations like that if able you simply move your arc over before you start. If you can't make a tight right then you either go around the block or get turned around where you can make the easier left hand turn.

The one's that question mainly are newbies. The little trains that could!

 

trailers drift to the inside of the turn. the longer the trailer the more it drifts, the longer the tractor the more area on the outside of the turn necessary. It has nothing to do with confidence, it's just the actual real estate required to make the turn and the size of the truck.

If I can start and end the turn with my tractor 10' further away from the curb that gives my trailer much more room as it comes around.

 

You just know, after a while.
You can look at a turn you're pulling up to, and guauge the turning distance. It's like shooting a rifle; once you do it so many times you learn to gauge for projectile drop and windage without giving it much consideration.

I suppose depth perception and spatial awareness has the bulk of mental process that go into something like taking a turn, but at the end of the day most drivers have come up to atleast one or two turns they found out they couldn't make before its too late. That's when you shut the road down until either a nice pedestrian or a pissed cop helps you out.

 

Tho I can't match the years of experience of Condo or others, I am sufficiently experienced in knowing my tractor/trailer's turn tracking, and judging the various turning "conditions" we face. I understand what you are trying to determine, and even tho you want to concentrate on a mutually beneficial acceptable corner radius, with no regard to the roadway width, the "practical usable roadway width" would be the most significant factor involved. The design and adjustment +/- of radius would follow that.

By "practical usable roadway", it means just that, as it relates to the truck's path just prior to actual turning.
A skilled driver knows what his truck is capable of on any entrance or intersection, as related to roadway width or any curb radius.
The bumpouts, imo, can be a significant factor IF they reduce the maximum "practical usable roadway width" to a point where it's virtually impossible for trucks to turn. I say this with a right turn in mind, as I'm assuming you'd want to eliminate any "left turn only" truck accessibility in your design.

Having done "some" past curbing construction at intersections with various radii specs, and now with the experience of tractor/trailer driving (albeit only 2 years), in my opinion I believe there is a substantial difference between a 20' & 30' radius, as it pertains to T/T turning without sufficient practical usable roadway width.
However, it's far less significant for "occasional" or low truck traffic locations, but significance increases greatly for repetitive or higher truck traffic expectations.
Also, I'd feel safe in saying that although it would have far less bearing on experienced drivers, today's truck traffic (and driver) comes in all shapes and sizes. That 30' radius curb/parkway will most likely be absent of many tandem tracks, whereas there may end up being plenty, with time, on the 20' radius curb/parkway. jmo

I'm saying this strictly from a practical viewpoint, not an engineering point of view. Also, I'm saying this without knowing the most important factor (road width).
As skilled drivers, we are confident before and during the turn. There's no room for no confidence. No matter what the radius or road width is.
Again, jmo.

 

I've never actually gotten out and measured the radius of a turn, it's just a judgement thing that comes with experience (as others have already said). Right turns require a wider swing than left turns in most cases. There's been plenty of times (had one in Chicago just last week) where my gps tells me to turn down a road and all I have to do is take one look and know its just not gonna happen. Also, sometimes I have to wait for traffic to move before I can make a turn, so I don't take the hood off of a car. I guess some are just better tHan others at judging trailer walk, and experience helps too.

 

There is a substantial visual difference between those two radii, with the curb setback 12.4' and 8.3', respectively, from the imaginary meeting point of the curb lines. Now that said, without going to town and eyeballing the curb radius, both those seem to be fairly generous radii. I mean, a 12' setback is roughly a lane width, and about 94' of arced curb length.

What is a standard radius city street curb?

 

I'd like to hear from the OP, but in the meantime (although it's been many years ago) in the Chicago area the minimum standard radius on the city street intersections was 10' radius, but depending on variety of roads/streets in that area it did range up to about 18' to 20' curb radius.

The bumpouts can make for a necessary increase in radius, depending on how much they intrude into the roadway, and how much practical roadway space they leave.

 

After a bit more number crunching, the 30' radius would require about 34 degree turn, while the 20' would need 45 degrees; figured with a nominal 40' kpa trailer.

 

Interesting. I'm sure you could teach me a thing or two on trying to calculate/figure those angles & tracking.
Most of my opinion was based on relative varying radii and estimated tandem tracking via intersection experience, if that makes sense.
I'm on overload with several other ongoing issues and the ol' brain cells just "won't go there" without a good fight.