This is a really good diagram of a semi going through a right turn. It really demonstrates that the trailer does not follow the tracks of the tractor. I don't know how many times I've had cars try to wedge themselves to the right of my rig, planning to beat me to the right turn instead of just giving me the room necessary to complete the turn. Usually, this doesn't result in success for them. What generally happens is they have to back up to keep from having my trailer run over their hood, thus destroying the time advantage they were to anxious to attempt to accomplish. This, of course, is not their fault - because as a rule I'm informed that I'm number one down the street a ways when they pass me. I guess the turn signals on the rear of the trailer, the side of the trailer, and the side of the tractor aren't clues enough what my intentions, clearly indicated in a significant amount of time, are. Just my mere existence on the highway in their way harshes their mellow. Of course, if I didn't stomp on the brakes during those territorial disputes, their cars along with their mellow would be extremely harshed. And the citation they would receive, as well as the increase in their insurance, wouldn't really make their day.
Sometimes, to enter a narrow street with a lightpole on the corner, the tractor has to swing over into the oncoming lane of both streets - the one the semi is on, and the one it is turning right to access. Longer trailers - and longer wheelbases - require a bigger swing. So, your local delivery guy, with the single axle tractor with the short trailer with a single axle, can take those corners without needing nearly as much room. There are differences even with the longest "legal" trailers (legal as in they don't require over length permits just to move), which are 53' long from end to end.
This is a typical 53' dry van with sliding tandems. Depending on how the trailer is loaded, the tandems might have to be adjusted fore or aft to "axle out" the weight of the payload. However, most of the time the axle group is tucked fairly far under the trailer, so this rig is a little easier to get around a corner.
This flatbed would be the other end of the spectrum. It's referred to as a "spread axle" for the obvious reason - the axles are spread apart. This is done so the group can carry more weight legally than a normal tandem group. This is because of the "bridge law," which is more accurately known as the Federal Bridge Gross Weight Formula. This is a subject that deserves far more attention than it's gonna get here - but we'll just say that the standard tandems are usually allowed 34,000 lbs, and the average spread axle group is allowed 40,000 lbs if the spread is long enough. Single dual wheel axle groups are allowed 20,000 lbs, for instance.
At any rate, that trailer is going to be harder to get around a corner than the dry van. When the trailer is loaded, the pivot point is going to be in the middle of the group, in front of the rear end. However, a lot of trailers like this are set up to pick up an axle when the trailer is empty. Doing this saves fuel and wear on the some of the tires. It's usually always the front axle, so that is going to make the turns even more difficult.
We have several "double drop" trailers with both single and tandem axles - and they are moved all the way to the back. I've marked many a curb with those puppies - sometimes there is no choice.
This pic is a pretty decent representation of what I can and can't see around me when I'm empty. When I'm loaded with a wide load, it's even worse than this. The side zones are not symmetrical because the driver sits on the left side, and the mirrors are adjusted accordingly. I also think I can see a bit more than the zone shown here with my spot mirrors. On either side, there is definitely a blind spot when a car approaches my side window. If a car is right beside me, but I can't see it when I look out the side window, and it's even with the front of the trailer, it's pretty difficult to see it even with the spot mirrors. Which is why I check my mirrors several times before signaling a lane change.
But it doesn't do me any good to check thirteen dozen times if a car keeps station in a blind spot. If I check thirteen dozen times and don't see it because the driver has chosen to keep his vehicle next to me for some time in the same spot - not much I can do about it.
So, it's my hearty recommendation that in normal traffic, one shouldn't "park" next to a semi on multilane roads. Either pass the truck, or let it go by. Even if letting it go by might cause the driver to lose "the race" to where ever, violating the "don't let the slow semi get by at any cost" mentality.
That is another subject and gripe for another day but honestly - if my cruise is set four or five mph faster than someone else, and I gradually catch them, all it takes is for me to put it in the fast lane to see the "don't let that big truck get by field" take effect - it's just like I pushed the car ten mph faster. However, most of these people don't seem to realize that if they don't change their cruise setting I'll be catching them almost immediately again. And again. Ad infinitum. Or if they aren't using their cruise control, they'll settle back into their "comfortable speed." Which is slower than I'm driving.
But, back to the rear view thing - the diagram above shows the "No Zone" extending behind the trailer in parallel lines. This really isn't true, or we'd never know what is behind us. Our mirrors (on normal, legal width trailers) are actually a bit wider than the trailers, so the rear "No Zone" actually narrows to a point some distance behind.
So, in conclusion, if ya don't wanna be crushed or smashed (or just plain run off the road), don't try to turn inside a truck during a right turn, and don't live in a truck's blind spots. Either speed up or slow down.
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Excellent analysis, Jeffro.
Whats the story on us 4 wheelers flashing our headlights to signal a passing semi that it is OK to come back into my lane. I do this when traffic is heavy and the semi passing me has a big pile of speeders on his tail as he is passing me. I know that if the trucker doesn't get back into my lane quickly, one of the cars behind him will cut over as soon as he can, then proceed to pass the semi on the right, making me nervous.
Hey, I always appreciate someone flashing their lights to let me know I'm clear - and I flash my marker or four ways back to thank the considerate person. Lots of drivers don't bother - they don't light up for other semis passing them, nor do they thank those who light them up.
I guess good manners are scarce with everyone these days.
Good read. We need mandatory driver testing and stupidity suppression training.
Fascinating. But then I always give you trucker guys all the room you need. But then when you drive a Prius, every other vehicle has to be respected. Even kids on skateboards.
But too bad the people who really need to read this article won't.
Everyone should have to drive a truck for a week before they get their car drivers license!
Hell, they bother me when I am pulling my 22 foot horse trailer.
Let's say I know just enough physics to make me dangerous.
A few trailers I've seen have borne the legend, "If you can't see my mirrors, I can't see you." This seems consistent with the No-Zone map.
I do try to avoid pulling alongside unless I'm actually going to pass.
Is there a good summary of flashing headlight signals etiquette in US? They differ a lot between countries. Where I learnt to drive flashing from a car moving in the same direction is always a warning signal, either "let me pass" or "don't you dare", so it would never occur to me to use it in a way described above. (flashing from an opposite direction meant "police speed check awaits you" :-) )
As for not staying in the blind spot this ought to be the normal behavior regardless of the other other car size or relative position. The morons who like to stick to another car and block their lane for many miles ought to have their license suspended. Either pass or slow down to leave a gap sufficient for others to use.
Anon: Your summary of flashing light codes apply here in the States as well - but good luck getting left lane hogs to recognize that they need to move to the right when they get flashed. I think they figure they own that lane, and if you wanna pass, you can damn well do it on the right - even if it's wrong.
The only other addition would be the flash to let a trucker know he's clear when the truck is passing and the passed vehicle courteously informs the driver that the rig is past and it's safe to change back to the right lane. It used to be more common - particularly between truckers. I suspect that is where the practice started, and auto drivers picked up on that.
It's just a nice thing to do for a large vehicle - even a motorcoach towing a car, or a pickup pulling a camper or horse trailer - or similar rigs where judging the location of the rear of the trailer in relation to others on the road is difficult.
Oh, and thanks for stopping by!
Why do big trucks make wide right turns, but not wide left turns?
You know those big semi-trucks with trailers that you always see on the highway; most of them say, on the back, "Caution: Wide Right Turn." I've never seen one that says "wide left turn," hence my question, why do they make wide right turns and not wide left turns??
They do. There is more room making a left turn, and it is less likely that the semi will have to use another lane. Just look at how the trailer swings.
Your name is "Extendable Trailers?" Now why wouldn't you know this in the first place? Or perhaps you are spamming for your site? Take a wild guess which one I think it is.
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