At low speeds, below about 15 miles per hour (m.p.h.), risks are low and increase relatively slowly with small increments in speed.

FORBES: In Crashes, Low Driving Speed Can Cause Serious Injury and Death to Pedestrians, Report Finds

The Brighton line, which carries B and Q trains through southern Brooklyn, was closed for an hour Tuesday morning after a report of a suspicious package near the Avenue H subway stop.

WSJ: Mayor Sets Precautions Following Boston Marathon Explosions