Speed limits and health

In 2012, the Massachusetts Legislature considered a bill to lower default speed limits on local roads from 30 miles per hour (mph) to 25 mph. Because traffic speeds affect road safety and air quality, the Speed Limit Bill could have far-reaching and important public health impacts. The Metropolitan Area Planning Council (MAPC), in partnership with Massachusetts Department of Health (DPH), conducted a Health Impact Assessment (HIA) that examined potential health impacts of the proposed bill. Based on a literature review, case studies, and statistical models, this HIA predicted that the bill would have a positive public health impact, particularly by preventing traffic fatalities and injuries. Potential co-benefits include enhanced walking and biking environments that may encourage physical activity, as well as increased desirability of properties on local roads due to quieter and safer streets. The HIA also concluded that the bill is economical. The Speed Limit Bill could prevent 2,219 crashes per year, 18 fatalities per year, and 1,239 injuries per year, which translates into a savings of up to $210 million annually in prevented medical payments and work lost. These economic benefits outweigh the costs of increased time spent in traffic and fuel burned, as well as the health impacts of the small increase in air pollution, associated with the proposed change. Because road design features and enforcement also help to determine traffic speeds, the HIA recommends that municipalities should implement traffic calming interventions and educational and enforcement campaigns to maximize the safety benefits of the bill. Improving bicycle and pedestrian facilities in concert with a speed limit reduction would likely be more effective in fostering walking and biking than would a speed limit reduction alone.