Well for one it's Fn illegal as truck spacing is somewhere around 200 feet on hiways. (don't quote me on that number though, I always know it as about three tractor trailer lengths).
Two main reasons for this, 1) So as other traffic including other tractor trailers can overtake and can fit in between. 2) So as to leave enough room for emergency or sudden braking.
Obviously 5, 6 guys running that close together is not smart, however it is called drafting and they swap lead position from time to time, if at all polite they would distance themselves when doing hill climbs as the lead tractor would then be doing more work while others are tucked in getting pulled uphill at a lesser RPM.
This is all a small fraction of fuel savings but it all helps as far as they are concerned. It's not smart by no means.
When you get to tail another truck, there is a certain distance where the wind turbulence is too great and begins to rock the truck side to side, gets into a wobble, it's not smooth, it's actually fighting it and worse on fuel mileage but they won't hang back the mentioned 200 feet for other varies reasons. One guy might be lighter/heavier then the next guy. On small hills they'd bunch up again.
5 or 6 guys could be jappin on the CB and just get lazy then settle in a drive together for the day like that, others may tuck in behind and join in. The view is not great but the day/miles passes quicker when engaged in conversation with others, next thing you know you're in another part of the country and your done for the day.
When they get to that 30' or even closer, the RPM's literally drop down and is being pulled by the harder working truck up front. If the head winds are real bad, they'll do it more often. I forget the number but after a certain amount of trucks, I think it may be around 6 or so, they begin to call it a convoy which is also illegal nowadays.
For the most part I feel it's a few guys that end up catching up with each other and they may be governed at a certain speed and thus have already establish that passing is going to take for ever, specially with already 4 or 5 guys running in a line. They just tuck in behind and get lazy, foot in the oil pan kinda thing. Won't go any faster so we'll just do this behind the others all day.
It's not that they do it on purpose, it's actually frowned upon to be running too close like that, for the drafting, your ripping the guy ahead of you off and should there be a need to suddenly slow down, it's too lose for comfort as reaction time has severely dropped because they got too lazy for too long. Not too mention the up ahead visibility has been reduced to staring at brake lamps, too see if and when they come on. Hard to see in the sun also.
Also, newer model trucks nowadays have that up head collision avoidance, basically a buzzer that goes off when too close to something in the front, they follow at the magic number to keep the buzzer quiet.
I know when I run at night up towards Canada West, it's for the most part two lane highway and the Moose at night is a huge problem, I've seen plenty of Moose coming around the corners where they are just getting back into the ditch, I've also seen plenty of illegally ditch parking going on including whole tractor trailers flipped right over laying sideways across both lanes because they swerved suddenly and lost control. At such travels it's not too smart to be running up tight like that although it happens often.
Myself, I've been known to warn some on the CB, if no response, I've been know to light up the rear wheels to make them Fn back off, next upcoming passing lane, I'd signal them to get ready, wind up their rubber elastic band and sling shoot that set up around me. Get them away from me, They are either dangerous or in too much of a hurry. However, Again, I'd be guilty of doing it myself as well at times. Sometimes you hear on the CB, "Hows your fuel mileage back there?" ... it's a polite way of say, BACK OFF or GO AROUND!!!!
It's definitely not smart or legal but it get's done all day every day by all, weather permitting. It's mostly done to get out of the turbulence. Too close and it's called drafting which upsets some other drivers, it's a huge safety thing obviously.
Often I look into my drivers side mirror to only see nothing but headlights and I'd already have my foot into all they way. He's playing gopher back there trying to look around ya because he does want to pass. Getting crazy and angry can only result in tragic accidents, I always remind myself to remain professional and on the straight always help them around by signaling into that lane ones at a time and show them my brake lights. This means, get around me, it's safe to do so, stop ridding my ass!
Other times, I've Fn lost it, I've locked it up once and felt the f*cker kiss the rear end of my trailer, not cool!
But yeah, they get lazy and settle in and run that close all day, they'd have to get even closer then 30' to make a real difference in the drafting for fuel mileage savings.
Enough about trucks and their stupid drivers, I requested the week off and enjoying getting some decent rest and finishing a few things around the house. It's a nice break from driving all night all week.