Friday, January 29, 2010

Tysons Neighborhood Traffic Impact Study

The Neighborhood Traffic Impact Study developed by Fairfax Dept. of Transportation, was conducted to assess the impact of future development in Tysons Corner on neighboring communities. These are the communities where using a bicycle to get into and around Tysons should be a viable option for many short, local trips.

As with many "traffic" studies, there is no mention of bicycling and walking. The contractor selected 19 intersections for analysis, using two levels of future density in Tysons and looking at the modeled impact of that development on traffic delay (Level of Service or LOS). Where intersections "fail" with a low LOS, mitigation measures, such as added through or turn lanes, are recommended. The impact of these "improvements" on pedestrian and bicycle levels of service isn't considered.

As Greater Greater Washington explains in The only thing we have to fear is fear of traffic, this narrow view of how the world works isn't very effective when it comes to analyzing how cities work:
The math seems simple. If you build new houses, stores or offices, they will generate a certain number of trips. Roads have set capacities. The added trips will therefore increase congestion and decrease Level of Service (LOS). To avoid congestion, many areas have Adequate Public Facilities ordinances requiring developers to widen the roads.

That's a straightforward formula for adding suburban sprawl. It's the system that built Tysons Corner. But strangely, when a plan comes up for building a real city, people balk. It could never work. It'd generate way too much traffic.
Despite increased growth in the Ballston Corridor, traffic congestion has not increased; people live in mixed-use communities near transit and they walk, bike, and take transit. These factors are often not properly handled with current traffic models.

See a related post at SF.Streetsblog, Paradise LOSt (Part I): How Long Will the City Keep Us Stuck in Our Cars?.

[It should be noted that despite the above rant on LOS, the conclusion of the Traffic Impact Study was that: "revising the existing Comprehensive Plan by considering the GMU High Land Use Alternative will not cause any significant traffic impacts in the study area."]

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