Thursday, May 3, 2012

Road Diets

The neighborhood associations of Mistletoe Heights and Berkeley Place, both part of a historic preservation district in the city of Fort Worth, Texas, recently passed measures encouraging the city to consider a “road diet” for the four-lane road that transects these neighborhoods.  Planners Dan Burden and Peter Lagerway coined the phrase “road diet” in the 1990s to refer to the transportation planning technique of reallocating existing roadway space that is providing excessive carrying capacity in a manner that results in a reduction in the number of vehicle lanes.  For example, a road diet might involve the conversion of a four-lane, undivided road to a three lane road, whereby the land previously used for the fourth lane can be employed for other purposes, such as the creation of a two-way left turn lane and either defined bicycle lanes (image A below), wider sidewalks and landscaping (image B), or angled/parallel parking (image C), or some combination thereof.  

Image A, courtesy of HoustonTomorrow.


Image B, courtesy of Houston Tomorrow.


Image C, courtesy of Streets Blog.

Proponents of road diets generally cite to more efficient roadway usage, reduced vehicular speeds and crash rates, and the promotion of walk-able and cycle-able communities.  (This video provides a nice summary of these and the related benefits of road diets.)  In addition to these social and public health and safety benefits, it seems that road diets, when implemented on appropriate multi-lane arterials, also can provide a number of environmental benefits.  For example, bicycle lanes and expanded sidewalks can reduce dependency on automobiles (and thus reduce the environmental risks associated with the fossil fuels that power them).  Moreover, landscaping can reduce impervious cover (and thereby reduce stormwater runoff and improve water quality), offer cooling shade, and provide vegetation that can serve as carbon sinks. 

Nevertheless, road diets are not universally supported.  Opponents fear that traffic volume might exceed the capacity of the reduced lanes.  Additionally, some suggest that road diets can either (i) reduce the speed and reliability of public transit service where bus stops are located in pullouts and buses have difficulty re-entering traffic, or (ii) increase overall traffic congestion given that it will be more difficult for motorists to pass buses that make frequent stops. 

It will be interesting to see whether and how this latest, grass roots effort in Fort Worth, and related efforts across the country, prompt local land use entities to formally consider the environmental benefits of road diets in deciding whether the potential advantages of road diets outweigh the risks.

-Tim Mulvaney

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