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Safer traffic, for one thing.

From a traffic engineering perspective, one-way streets are all about speed. Without the danger of oncoming traffic, one-way streets can feel like an invitation to hit the gas. But swift traffic flow isn’t the only factor by which progressive cities judge their streets, and as safety and livability become more important, a number of metros have found the case for converting one-way streets into two-way streets a compelling one.

Count Louisville among the believers. In 2011, the city converted two one-way streets (Brook and 1st) in the Old Louisville part of town. Though originally designed as two-way streets, Brook and 1st became one-way after World War II, in keeping with the car-first engineering of the time. In championing the change, local official David James cited the need for calmer streets and economic development.

A pair of planning scholars has evaluated just how well the safety and economic claims held up following the street conversions. In a word: very. William Riggs of California Polytechnic State University and John Gilderbloom of the University of Louisville report that compared with nearby, parallel streets that remained one-way (2nd and 3rd), Brook and 1st experienced fewer collisions, less crime, and higher property valuations.

Let’s take a closer look at some of the key findings, via the Journal of Planning Education and Research.

(Via Journal of Planning Education and Research)

Traffic safety

Riggs and Gilderbloom tracked traffic collisions on Brook, 1st, 2nd, and 3rd for five years leading up to the conversion, and two years after. In the first year following the change, both Brook and 1st had big drops in collisions per month, while those on 2nd and 3rd increased. At the two-year mark, the per-month averages on Brook and 1st were down 36 and 60 percent, respectively; meanwhile those on 2nd were up a lot (23 percent) and those on 3rd were only down slightly (7 percent).

What makes the finding even more impressive is that traffic safety improved on Brook and 1st even though traffic volume increased on these streets—13 and 40 percent, respectively. Over the same period, traffic volume on 2nd and 3rd dropped. In apparent real-world confirmation of theoretical traffic models, drivers seemed to accept the slower speeds in exchange for more direct access to their destination; here’s Riggs and Gilderbloom:

It is also one of our more surprising findings since traffic engineers typically claim that two-ways reduce maximum capacity of a road, making it inefficient use of tax payer money and resources…

Brook Street in Louisville (top) was converted to two-way traffic in 2011; parallel 2nd Street (bottom) remains one-way (via Google Maps).


On criminal measures of safety, the converted Brook and 1st performed as good or better than 2nd and 3rd streets, too. After the change, the number of total crimes per month declined on both Brook (15 percent) and 1st (30 percent). Crime on 3rd also fell (16 percent), but crime on 2nd increased (16 percent) and crime across the Louisville metro increased 5 percent during this period.

Riggs and Gilderbloom found a particularly impressive dip in two specific crimes. Auto thefts fell on Brook (33 percent) and 1st (23 percent), even as they rose on the comparison streets. Robberies also fell on Brook (33 percent) and 1st (50 percent)—a greater decline than on 2nd and 3rd (13 and 10 percent, respectively). The researchers don’t have a terribly compelling theory for the change, but suspect that slower getaway speeds could play some role. It’s also possible the traffic increases mean there are just more proverbial eyes on the streets.

Property values

On property values, the same improvement story held true. Examining property sales before and after the conversion, Riggs and Gilderbloom report that houses on Brook and 1st both appreciated, with an average increase of 11.6 and 2.8 percent, respectively. Those on 2nd and 3rd, meanwhile, depreciated roughly .4 percent over the same period. The latter cases are representative of the larger Louisville real estate market, which declined slightly during this time.

Again, the source of the improvement here isn’t entirely clear, but the researchers suspect that people simply prefer to live on a street with slower traffic, less crime, and better mobility.

No panacea, but lots of promise

The researchers recognize some limitations in their analysis. The process of neighborhood improvement is a very complex one with lots of variables. The statistics used here can’t quite show that the street conversion itself caused the changes, though the inclusion of very reasonable control streets does lend more support to that idea. And these conversions aren’t cheap: in this case, $250,000 for the pair of 1.25-mile segments.

But as more evidence emerges about the safety and economic value of one-way street conversions, those cost may start to seem well worth the greater good; Riggs and Gilderbloom conclude:

Though there is no panacea for improving neighborhoods, our case shows a clear example of road diets and traffic calming as ways to change the character of a neighborhood and that one-way to two-way street conversions can assist in redeveloping a community.

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