Counter-Intuitive

Patrick Kennedy, writing at Walkable DFW, on the counter-intuitive nature of traffic planning:

Have you ever noticed that virtually everything about traffic planning is counter-intuitive? Mostly, that is because the real world works opposite the way traffic engineering operates.

Here is a pretty fascinating study by the HSIS (Highway Safety Information System) looking at road diets from Iowa specifically (15 sites) as well as around the country (30 sites in addition to the 15 in Iowa). Predictably, “accidents” (shall we say collisions) dropped on average from 23.74 to 12.19 yearly accidents per mile averaged from the Iowa sites and 28.57 to 24.07 on the nationwide HSIS sites. Though the information isn’t provided regarding average speeds before or after, we can hypothesize that the severity of the accidents diminished as well.

More interestingly however, is that average daily traffic counts actually INCREASED when reducing the amount of lanes on a road. On the dieted Iowa roads, traffic (vehicular only) increased from 7,987 to 9,212 cars per day. On the 30 HSIS dieted roads, traffic increased from 11,928 to 12,790. More traffic, slower roads, safer.

Patrick has some interesting thoughts on why this is.