A bike box is a painted area in front of the stop line. It permits cyclists to advance to the head of the queue of vehicles and go into the intersection first. It is especially useful when making turns. The motorist must stop at an advanced stop line considerably short of the intersection where motorists are used to stopping. It protects the safety of cyclists for left, right turns and straight through motions.
In Boston, I saw one hundred percent respect by motorists for the bike box. Otherwise, motorists were quite aggressive. Every car stopped at the advanced stop line. In London England, no motorist would be caught dead respecting a bike box.
Boston motorists were aggressive. So were pedestrians. Walk signals at most intersections were pitifully slow, late, delayed, or otherwise made inconvenient for peds and catered to motorists. The walk signals counted down from the first moment the walk signal came on (Ottawa’s count down only on the dont-start phase).