<p>I am traveling on the interstate in the right lane. It is a two lane highway at that point I am behind a truck traveling 55-60 (a semi - a big one), and I would lke to travel 65 (the speed limit). I signal and change to the left lane to try to pass the guy. As I try to pass, the truck speeds up, I end up going over 80 in order to pass him (all the while praying that I don’t get a speeding ticket). Once I finally do pass him, he slows back to a slower speed and he becomes lost in the rearview mirror.</p>
<p>Does my act of trying to pass him actually make his truck go faster? Oh also, if I give up and slide back in behind him, he always slips back to 55-60 mph. It happens so often that I am beginning to wonder if it is something other than bad driving.</p>
<p>Happens passing cars, too. I think drivers subconsciously pace themselves against the vehicles around them, with “vehicle next to you” a stronger trigger than “vehicle in front of you.”</p>
<p>On a hilly road, it’s physics, and you leapfrog the semis. On a flat road, it’s psychology.</p>
<p>A car is perpetually on the left passing lane at the same speed as the car on the right lane going way below the speed where most cars normally go on the passing lane. Eventually after a long while the car passes all the cars on the right and continues to stay on the passing lane. After a few moment, you decide to try to pass on the right, the car speeds up not letting you pass. Eventually it comes to another group of slow cars on the right and then again it slows down seemingly to the same speed as those right lane cars.</p>
More likely for a car. Less likely for a truck (takes longer to accelerate). It may be your perception.</p>
<p>From a physics stand point, when you get right behind the truck, you help the truck go faster. You help fill the void behind the truck that sucks the truck backwards. If there is some effect when you are beside the truck, it would be very slight for the truck.</p>
<p>And driving in your blind spot. I suspect that it’s to avoid speed traps in the right lane as you are their shield. What’s annoying is when you come up to a car in your lane and you try to decide whether or not to move into the left lane to pass while the other car is blocking you from doing so.</p>
<p>Certainly some people will speed up when someone’s passing them but I think there can also be other factors at play - </p>
<ul>
<li><p>Perception - once one starts passing the truck a certain amount of anxiety sets in where the car driver knows they must pass the truck before a vehicle comes the other way. This is compounded if there’s a curve ahead or traffic coming the other way can be seen (even though it’s still safe to pass) and that point is getting closer every second. The truck is long and the passing time is often longer than it was expected to be, especially if you drive a gutless car, and the relative speed of the pass is only 10 or 20mph. In this case, the truck continued driving the same speed and it’s the car driver who isn’t handling the perception properly.</p></li>
<li><p>Practical changes in the road - Trucks tend to go pretty steadily on a level straight road, increase in speed downhill, and decrease in speed uphill. If the car driver thinks “goodie, there’s a nice downhill stretch where my Prius will really move to pass the truck”, then they’ll likely run into the issue of the truck increasing its speed (combined with the perception issues above). If they pass the truck on an uphill thinking “goodie, the truck will slow down uphill and even my gutless Prius can go faster than the truck uphill” they may have an easier time of passing the truck but still will run into the physics of having a harder time speeding up to pass on the uphill and then one must combine the anxiety issues above.</p></li>
</ul>
<p>I’ve found most big rig drivers to be pretty good in this area and fairly predictable with the flats/uphill/downhill but there are exceptions of course.</p>
<p>And then there’s the classic movie that you should watch if you haven’t yet - Duel with Dennis Weaver (1971 movie).</p>
<p>What bothers me is when you’re going pretty fast in the passing lane (10-15 above the speed limit) and then someone tries to pass you on the right (I’m not increasing my speed here :D) but they take too long. One time this happened and we approached a red light in which only the middle lane could go straight and the other person, whose lane had to turn right, was half a car length ahead of me and they put their indicator on. Did I let them in? No.</p>
<p>If I’m on a two lane road and driving significantly faster than the speed limit with passing not allowed and some a<strong>ho</strong> tries to pass me, I step on it. I’ve had people pass me going 90 on a back country road.</p>
<p>If someone is going faster than me and wants to pass me, especially on a 2 lane highway in the countryside, I’ll do what I can to assist the person in passing me including moving closer to the right, maintaining a constant speed, etc. I’ll only do this once though - if they pass me then slow down to slower than I was going before, which sometimes happens, I won’t make it easy for them to pass me again (after I pass them of course). </p>
<p>This scenario of passing then slowing down is more irritating than the scenario of the one being passed speeding up for the pass IMO because you have to keep dealing with them. </p>
<p>By letting the passer pass me readily, it’s not only safer for all of us, but it makes it more likely that the person who passed me will be the one caught in any speed traps ahead. In some cases I’m quite happy when someone wants to pass me since by definition they’ll all be driving over the speed limit and hopefully catch the speed traps while I cruise on by them. This is a most satisfying feeling.</p>
<p>If someone wants to pass me (esp. on a back road), I <em>always</em> slow down and let them go. I don’t want to be the one who causes an accident and I don’t know if they have an emergency or other problem. That said, if I’m going to pass a truck or another car, I do it with the accelerator floored for the entire pass, so it takes as little time as possible.</p>
<p>The “speed up when being passed” phenomenon has been studied in the context of parking spaces. In brief, people take more time, not less to pull out of a space when they see another car is waiting for it.</p>