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The idea of putting roads on diets—essentially shrinking the width of driving lanes to slow vehicles down—is a common topic in the recent discourse of how we reduce traffic fatalities down to zero. Multiple cities around the world have instituted such policies by shrinking lanes for vehicular traffic and adding bicycle and pedestrian improvements.
Cathy Tuttle, writing in The Urbanist, argues that while reducing the width of lanes on urban streets is a key component in slowing traffic to make streets safer for all users, the same may not hold true for highways and other designated truck and transit routes. Citing the fatal crash of a Duck Boat on Seattle’s Aurora Bridge in September, Tuttle notes that the bridge stands out as an example of where narrower is not necessarily better for promoting safety.
“… Federal standards for highways recommend 12-foot lanes, in addition to shoulders wide enough for emergency parking and median barriers. Most lanes along I-5 are 12 feet wide. The Aurora Bridge lanes are 9.5 feet wide…
Lanes on highways need to be wide to accommodate wide vehicles moving quickly. Traffic on the Aurora Bridge is posted 40 MPH, while people driving average more than 10 miles an hour faster (p.19 here [PDF]). The Aurora Bridge has had 144 crashes since 2005.”