90 degree alleydock and 45 degree alleydock

The other day I overheard one trucker tell another trucker about the process at his trucking company to upgrade from a student to a solo driver. He said that during the driving tests to upgrade at his company, a student had to do both a 45 degree back and a 90 degree back. And at various times in my career, I have heard other truckers talk about doing 45 degree alleydock backs and 90 degree alleydock backs. The only company I ever drove for in which I had to do a back to upgrade was at Covenant. Covenant never said the name for the type of alleydock back that they have on the upgrade test. They just call it an "alleydock back".

I'm curious what the heck the 45 degree back is, and I am curious as to what the 90 degree back is. I know what a 45 degree angle is, and I know what a 90 degree angle is.

The phrases 90 degrees and 45 degrees are phrases used in geometry. The lines that make up an angle in geometry are called rays. I made some drawings with red lines used to represent the rays of an angle.

When a trucker sets up to back into a parking spot, if the tractor-trailer is straight, then both the tractor-trailer and the parking spot are rectangles, which means that the length is greater than the width. If one drew a line lengthwise straight through middle of the parking spot, and if one drew a line lengthwise along the tractor-trailer, and if where the two lines met is 90 degrees, then the set up would look like this:

Is the drawing above the set up for a 90 degree back?

When I first thought about this, I thought that the set up in the drawing above would be what truckers refer to as a 90 degree back. But then I asked myself what a 45 degree back would consist of. At first, I thought that a 45 degree back would be a back that starts with a setup like the set up in the drawing below:


The problem with my original idea that the drawing above represented the set up for a 45 degree back is that if one drew a line that ran lengthwise through the parking spot that represents the first ray of an angle, and if one drew a line that ran lengthwise through the tractor-trailer that represents the second ray of an angle, the two rays would make a 135 degree angle when they connect together, not a 45 degree angle.

If one had the tractor-trailer set up in such a way that a line that runs lengthwise through the parking spot formed a 45 degree angle with a line that runs lengthwise through the tractor-trailer, the set up would look like this:



It is self-evident that one cannot back a tractor-trailer into the parking spot with a set up like the one in the drawing directly above this sentence. If a tractor-trailer was set up like in the drawing above this sentence, the trucker would have to do a completely new set up to back into the parking spot. So obviously, the set up for the 45 degree back is not like the set up in the drawing directly above this one.

So what is the 90 degree back? And why do they call it 90 degree back? Where is the 90 degree angle?

What is the 45 degree back? Why do they call it a 45 degree back? Where is the 45 degree angle in the 45 degree back?

 

That makes sense. I believe you are right. Thank you.

 

Yeah I have heard a similar thing from other truckers in real life several times in my career. So I thought it was worth creating a thread about since I did not know what the 45 degree back and the 90 degree back are.

 

Posts like this are why I come to this message board. Moosetek's post is full of pithy information. Not only does moosetek tell me what the 45 degree back and the 90 degree back is, he also tells me the rational behind why the backs are called the 45 degree back and the 90 degree back. And moosetek's rational is very logical and makes sense. He showed me how my reasoning and premises were wrongheaded. And he did it all without any sarcasm.