Bicyclists' Black Boxes.

Cyclists have long had a rocky coexistence with motorists and pedestrians, who often criticize bike riders for a confrontational attitude, and for blowing through stop signs or otherwise exempting themselves from the rules of the road. Now small cameras — the cycling equivalent of the black box on an airplane — are becoming an intermediary in the relationship, providing high-tech evidence in what is sometimes an ugly contest between people who ride the roads on two wheels and those who use four.