polly: we lowered our default speed limit from 30 to 25 miles an hour. we pointed out that if you were involved in a crash where unfortunately you hit someone going 30 miles an hour, you're twice as likely to kill that person as if you hit them at 25. narrator: a second part of successful road safety, engineering, is physically changing the layout of roads. for example, new york's queens boulevard, which had become so notorious dangerous, it was known as the boulevard of death. polly: well, queens boulevard is a very, very challenging roadway, and as you can see, very wide roadway, lots of lanes of traffic, cars driving very quickly. so first of all, we've rationalized the design, closed some of the slip lanes, added a bike lane that you can see behind me, and improved the pedestrian crossing areas so pedestrians have more space and more time to get across the street. narrator: riding bicycles in new york has increased fourfold since 2000, partly made possible and safer by a multiplicity of new bike lanes like these ones. the city also changed the crossi