bicycle path crossings. Although the EPA MOBILE model would indicate that slowing down traffic typically increases emissions, empirical research indicates the opposite in many cases. Research in Germany has shown that the greater the speed of vehicles in built-up areas, the higher is the incidence of acceleration, deceleration, and braking, all of which increase air pollution. German research indicates that traffic calming reduces idle times by 15 percent, gear changing by 12 percent, brake use by 14 percent, and gasoline use by 12 percent (Newman and Kenworthy 1992, 39–40). This slower and calmer style of driving reduces emissions, as demonstrated by an evaluation in Buxtehude, Germany. Table E-1 shows the relative change in emissions and fuel use when the speed limit is cut from 50 kph (31 mph) to 30 kph (19 mph) for two different driving styles. Even aggressive driving under the slower speed limit produces lower emissions (but higher fuel use) than under the higher speed limit, although calm driving produces greater reductions for most emissions and net fuel savings (Newman and Kenworthy 1992, 39 –40).

Moreover, by encouraging more use of walking and bicycling and reducing the advantage offered by the automobile for short trips relative to these alternatives, traffic calming usually reduces the number of trips, trip starts, and VMT. Applied on a widespread basis in conjunction with transit improvements and transportation pricing changes, traffic calming may contribute as well to a reduction in household automobile ownership levels, further reducing emissions and travel demand. Thus, even under circumstances in which individual

TABLE E-1 Percentage Change in Vehicle Emissions and Fuel Use with Speed Change from 50 kph (31 mph) to 30 kph (19 mph) (Newman and Kenworthy 1992)

 

DRIVING STYLE

EMISSION TYPE

2ND GEAR AGGRESSIVE

3RD GEAR CALM

Carbon monoxide

−17

−13

Volatile organic compounds

−10

−22

Oxides of nitrogen

−32

−48

Fuel use

+ 7

−7



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