It allows residential streets to be 20 feet wide with parking on one side, or 26 feet with parking on both sides. The city notes that such streets maintain neighborhood character, reduce construction costs, save vegetation, reduce stormwater runoff, improve traffic safety, and make it possible to use scarce land for purposes other than motor vehicle use. The Portland Fire Department finds that skinny streets provide adequate access for emergency vehicles. It has been noted that it would be more economical to purchase fire trucks that fit local streets than to build all streets to meet the needs of the largest size trucks. Berkeley studies show that traffic control devices had little or no effect on police emergency response time, and Palo Alto found that bicycle boulevard barriers had not impaired police and fire emergency response.
Motorists are more likely to collide with pedestrians at higher speeds.
At 60 miles per hour, the field of vision of the motorist is two-thirds less than at 30 miles per hour. In addition, the probability of a pedestrian being killed is only 3.5 percent when a vehicle is traveling at 15 miles per hour, but jumps to 37 percent at 31 miles per hour and 83 percent at 44 miles per hour. Roadway geometry in safety-sensitive areas, such as schools, should keep auto speeds within 15 to 20 miles per hour. A German study found that traffic calming reduces vehicle idling time by 15 percent, gear changing by 12 percent, brake use by 14 percent, and gasoline use by 12 percent. This is in part because the greater is speed of vehicles in built-up areas, the higher is the incidence of acceleration, deceleration, and braking.