My dad has worked in construction and management for over 25 years. When my sister and I first learned how to drive, he told us one thing to NEVER EVER do to large trucks, 18 wheelers, and concrete trucks. My dad's words were "never, ever cut off a large truck. They can't stop fast enough." I've seen horrific accidents and tragedies because some genius decided to cut off a large truck.
This morning, while driving back to College town, I saw many people cut it close and one person cut off a large truck. My rule of thumb: whenever passing or merging into a lane with the large truck-always, always, ALWAYS give at least two to three car lengths between you and the truck. If you can't have two to three "cars" between you, then be sure that the truck driver sees you before you get in that lane.
This method has helped me in Downtown Dallas, Downtown Fort Worth, small towns, bumper to bumper traffic, and I am accident free.
Rule of thumb: Never cut off a large truck!!