I have noticed that the standard to which truck drivers are trained in the US falls far short of the standard to which truckers in more advanced countries such as, say, the UK are trained. In other countries, truck drivers actually receive instruction on how to manage interactions and especially conflict with other drivers. They are made aware that they are driving large vehicles of tens of tons of weight that are potentially extremely lethal, and that they have a professional duty of care to drive, well, professionally, even when other road users do not.
As you allude to, such professionalism is largely absent from the American trucking body, which is evidenced in a wide array of substandard driving exhibited by them.
Cars often accelerate in highway merges to get ahead of a truck and then slam their brakes on as soon as they merge to avoid hitting traffic ahead in the target lane. This can cause the truck to have to brake sharply, which is obviously not easy when it's carrying 40,000 lbs. So the trucker above clearly wanted to try to prevent this. However, the technique used in countries where truckers have more advanced driving skills is to simply slow down. This causes a buffer area to be created in front of the truck into which cars will continue to insert themselves, but the added distance created by the buffer will mean that the truck is much less likely to need to slam on its brakes. It's all about maintaining adequate stopping distances that are appropriate to the type of vehicle being driven. Again, not something that is taught, at least not effectively, at American trucking schools.
