Wider lanes and shoulders encourage faster driving, according to a new study published in the Journal of Transportation Engineering. Based on more than 650,000 observations of uncongested freeways, researchers from Texas A&M found that drivers travel 2.2 mph faster, on average, in 12-foot lanes than in comparable 11-foot lanes. Perhaps even more striking, wide left shoulders adjacent to 11-foot lanes can increase speeds by as much as 1.1 mph per foot of shoulder width, ranging from 1.5 to 11 feet. Unfortunately, the study also highlights how speed and capacity are often conflated in misleading ways and how safety can be ignored altogether.
A recent study indicates that raising speed limits on non-limited access highways from 55 to 65 miles per hour is likely to have a negative benefit-cost ratio when crash injury and fatality costs are fully accounted for. The analysis evaluated the costs and benefits associated with required infrastructure upgrades, travel time benefits, fuel costs (due to lower fuel economy), and costs associated with increased crash frequency and severity.