I think, as a truck driver who has found himself in similar situations with cars in front of me, I would like to think, whenever I see vehicles side by side three abreast on a major roadway that it is a situation that should immediately raise alarm bells, I would have recognized the inherent danger that traffic pattern could cause, and I would slow down, not knowing what the experience level or the give a f--k level of the vehicles ahead of me. It was of course the morning rush hour in the area, and truckers, if we have to be on the road at those times of increased risk, should have a heightened awareness of the traffic around us, and be willing to give space and room around us. Many drivers who are commuting aren't aware, nor able to recognize these high risk situations, and the truck driver should have. Whenever someone recognizes that they have no 'escape route' from a driving situation there should be enough room, at the very least, for them to slow down and remove themselves from the high risk situation they are in, without having to worry about being run over by a 'professional' driver.

Was it necessary to pass the SUV? This doesn't seem to be the case because you stated that traffic was flowing well. Before making a lane change to pass another vehicle, a motorist should always check their mirrors, blind spots and look far enough ahead and behind to determine if there are any obstacles. I can think of two reasons for motorists not checking their mirrors. First, they are driving too fast for the conditions and approach another vehicle quicker than expected. Second, they are tailgating (following too closely) and become impatient (aggressive) and attempt to cut over a lane to get around a vehicle that is impeding their progression of travel. It is entirely possible that you were traveling approximately 90 km/hr and the truck was traveling 140 km/hr (not uncommon on that highway from my experience, except it is generally the four wheelers speeding)and appeared in your mirrors rather quickly. At this point you're in the middle lane with the intent to pass the SUV and at this time you see a car on your left that appears to be trying to merge into your lane. Tapping the brake is really a mistake. In the U.S., new drivers are taught not to use their brakes on the interstate except for obvious reasons as slowed or stopped traffic. Drivers should always recognize which reaction is safer: braking or accelerating. In this case accelerating would have been more appropriate as you were passing another vehicle, followed by properly merging back into the slow lane. However, the vehicle to your left may still not have seen you and this is a clear example as to a time when you are supposed to use your horn. Specifically, the horn is used to warn another driver of an impending collision. This scenario happens everyday on the interstates and any given truck driver has seen it numerous times. I'm unaware if you were in a commercial vehicle, but I wonder why you were surprised by a semi truck coming up behind you? In any case, be safe and adjust speed to driving conditions: weather, traffic, etc.

Sounds like you did a good job. Once the car on your left started to move over, I would have given him a salute with the horn, but that is about all. Be safe out there.