Dangerous lane change forces driver off the highway
Driving on a multi lane highway can be a risky venture. Somebody is always trying to get ahead of the other vehicles, even if it means causing an accident. If you leave a safe distance between you and the vehicle in front, somebody will be on your tail, anxious for you to move up and tail gate the car in front. Or they will abruptly pass you and squeeze in, causing you back off more to allow a safe distance. They only get one car ahead by doing this and they risk the safety of everybody by following too close and cutting off other cars.
There is also the risk of the person who doesn't do a shoulder check to make sure a lane change is safe. They put on their signal and move over without any thought of who they are affecting. This person has made a lot of successful lane changes this way and they expect that their good fortune will continue forever.
In heavy traffic, you can't take your eyes off the cars all around you. There are rules of the road that make life easier, and if everybody follows them, there shouldn't be any accidents. Almost all accidents are caused by somebody breaking one of these rules.
This video shows a situation that happened in Ontario, on Highway # 403. One of Canada's busiest highways, it is five lanes wide in either direction on this stretch near Burlington. The driver with the camera running is in the left lane. The traffic is moving at roughly the 60mph speed limit (100km/h) and there are cars ahead of him. The Ontario Highway Traffic Act states that cars must move over to the right, when there is no traffic ahead of them. But traffic is moving smoothly and the vehicles in the left lane have a right to be there because they are passing the slower traffic in the right lanes.
Where things go wrong is when the SUV in the second lane moves up along side the car with the camera. He may have forgotten that the car is to his left, or he may have decided it doesn't matter. He put on his signal to change lanes. The law is very clear on this. He must signal with fair warning, check his blind spot, and only then can he move over, as long as the move does not affect other traffic. In this case, the lane change would put him less than a car length from the vehicle in front. He's already following too close to the vehicle in his lane, but it seems unlikely that he would want to be even closer to the car in front of where he wants to be. It also seems unlikely that he would move over while the camera car is to his left.
Trying to be courteous, the driver with the camera sees what is happening and he accelerates to get out of the blind spot and create room behind him. He will adjust his speed to create more room in front as they move along. As he picks up speed, the SUV just moves over into the lane. The car on the left is already moving past and braking suddenly won't be safe and it won't prevent a collision. Instead, he has to move over the rumble strip and onto the shoulder. He expects the SUV driver to see what happened and abort the lane change attempt.
Instead of braking and moving back to the right, the SUV accelerates and even squeezes past the other SUV in his lane. What seems to be an accidental move is now looking intentional as he keeps the car on his left from returning to the road.
As the car gets back onto the road, the SUV comes up on the left and tries to force the car off the road again. Partway through this, he decides to change lanes to the right and go around everybody.
In hindsight, the driver with the camera might have been better off to hit the brakes hard and allow the lane change, but nobody would ever expect the SUV to force his way over. The driver with the camera also had less than a second to make his decision as he chose to speed up and he was fully committed once he started moving past the SUV.
The SUV was mere inches from contacting the car with the camera at two separate times. The obligation to make the lane change safely was completely his. Whether he intended to force his way in and was angry or whether he just drives along without understanding how to make safe lane changes is impossible to know.
Following this incident, the SUV continued to tail gate other vehicles and it made numerous lane changes that forced other drivers to brake. Despite his abrupt and unsafe moves, he was not much farther ahead in the traffic.