Even though a tractor-trailer usually has three blinking lights to indicate an impending turn, many will not see them.  Since a truck requires extra time and space when turning, especially in the city, turning can be a dangerous thing to do.  Turning a tractor-trailer any direction requires vigilance, but you must be especially careful with a right turn.  Many city streets are too narrow for a truck to complete the turn without using space from another lane.  If you swing to the left before making the right turn, in order to make room for the trailer, be very careful to always keep the trailer as close to the curb line as possible.
  If you allow room to your right to open, even with all three signals flashing, there is a good chance a vehicle will try to get around you by passing on the right.  When you bring your tractor right and a motorist has snuck into the blind spot, they may crash into the side of the truck or trailer.  What makes this situation even worse is that by law this will likely be seen as your fault, since you were not in your own lane.  Of course, you probably could not have made the turn if you had not “borrowed” space from the other lane, but that does not seem to matter.  In this kind of situation, the burden is on you to protect people from themselves.