I can hear Psychosocial playing in my head when I look at this.

A lot of people are talking about the truck’s blind spot, but a part of it is also the passing vehicle’s “blind spot” that’s caused by the truck in front of it. When the driver sits on the left side of the vehicle, it’s easier to see around the left side of the vehicle in front of you when starting to pass. I’d you try to pass on the right, you have to be almost fully committed to the right lane before you can see around the truck.

Under normal circumstances that doesn’t matter a whole lot, but abnormal circumstances are what make it dangerous. Things like stopped or very slow vehicles in the right lane that the truck is try to pass. You try to pass on the right and end up rear ending a much slower vehicle that you didn’t see until it’s too late.

Plenty of other small reasons that add up to make it a “big deal” overall, but this one it seems a lot of people don’t think about.