Yeah, but . . .
An unsafe lane change, IF IT CAN BE PROVED, will shift the blame to the party making the unsafe change. It happens all the time on the DC Capital Beltway (people cutting in front of other people, reducing their "safe stopping distance.") If you're unlucky enough to do it in front of a cop, (on or off-duty) you'll get a ticket. If you do it in front of a vehicle with a camera (more and more commercials vehicles have dashcams) you'll be blamed. Any truck driver on the Beltway can tell you how often cars will zip in front of them never giving a thought how much they've shortened the trucker's "safe following distance" or how much more room a truck needs to stop quickly. So if you look at the cabs of newer trucks you'll see more and more cameras because of people who make unsafe lane changes. Here in the DC area people also cross solid lines to make lane changes, driving on the shoulders or in other areas where lane changes are not allowed.
A rear-ending of someone who has just gotten on the highway from the shoulder is NOT considered the fault of the driver hitting the merging car in the rear. When rejoining moving traffic from the shoulder, almost anything "bad" that happens as a result of that merge is the fault of the driver who is NOT on the main roadway. The problem most people have is that it's often impossible without witnesses or video to prove that the other driver is at fault. That's because of the strong presumption, as you've noted, of everyone to believe if you're struck from behind, it's the striking driver's fault
That's one of the reasons I picked up a very nice electronic color dashcam from Ebay that records up to several hours in ten minute segments, erasing the oldest stuff first when the memory card is full. I installed mine because I "T-boned" a car full of students who had run a red light. I remember being bathed in the green of the traffic light at the moment of impact, thinking "I'm going to die now and I had the green light!!!" It was a serious impact - I was travelling at about 50MPH and there were extensive injuries to the front seat passenger where my car hit.
Both cars were totaled and those sonovabitch students lied about what happened - I even HEARD the driver saying "this is my third accident - you've GOT to say it wasn't my fault or my folks will take the car away from me." I still fume thinking about it. Anyway, that's when I decided I needed a dashcam, just like the cops. Not only would it have shown who was in the right in that crash, despite four people conspiring to lie, it would show when someone did an unsafe lane change into the space in front of my car. If it showed me in the wrong, well, those SD cards are SO tiny it might just disappear!
So far, I've captured some pretty amazing "cut ins" on "film" (SD card, actually) but I have not been in any accidents while driving with the cams in place. On the DC Beltway during rush hour it is IMPOSSIBLE to maintain a safe following distance. When bozos see that huge, empty space they rush to get to it. If I am traveling in the inner two of four lanes, sometimes people from both adjoining lanes will dive for the same spot.
The camera I got was under $100 from Ebay. It records in an endless loop, plugs into the auxiliary lighter socket, comes on when the car is started and records for 1 minute after the car is turned off via a built in rechargeable lithium cell. Takes a standard SD card - I use a 1GB card because in reality, in a crash you'll only need about 30 seconds of the pre-impact video to prove who was at fault. The only real negative about the cam is that the date is GOD AWFUL difficult to set and if it sits too long without being driven, the internal battery dies and the unit needs to be hooked up to a PC to set the clock with a special batch file that's not correctly specified in the manual.
I moved that camera to my 20 year old Honda and installed a four-camera system in my van because it's got $25K worth of handicapped equipment and a single dash cam is not enough for "full protection." That takes a front, rear and two side view cams and a solid state quad recorder. Instead of using a "not likely to survive a hard impact hard disk, I got a 16GB CF card with an IDE adapter so there are no delicate moving parts to fail in a crash. That rig cost $300 for everything but I figure that's still less than my deductible.
Most importantly, if something like the "T-bone" crash ever happens again, I'll let those muthafu&kers lie their asses off to the cops before I reveal I have video of the crash so I can totally discredit them. It was a bitter pill to swallow to learn that if witnesses conspire to lie against the lone driver of the other car, judges and adjusters will believe them in a heartbeat. Never again! I ended up with a surcharge for three years because I was considered "at fault" by the insurance company. Sometimes, when I think about it, it makes me angry enough to wish I had killed the whole carload of lying little bastards. If there's anything I hate it's being "lied on" and blamed for something someone else did.
If you have any doubts about unsafe lane changes "trumping" the *almost* universal assumption that if you hit a car from behind then you're at fault, call your local State Troopers. They are usually well-informed about highway traffic rules.
Exceptions to Rear-End Auto Accidents There may be times when the driver who rear-ended you is not at fault or at least is not completely at fault. It is possible that you were partly a fault for the accident. Examples of where you could be partially at fault include the following:
a.. Your brake or tail lights don't work, especially if it is dark out b.. Your car has mechanical problems but you fail to move it off the road
-- Bobby G.