Keep most Loudoun roads more like this. Photo by Heather Elias.

Loudoun County is pushing a plan to widen huge numbers of roads across the county, but residents are fighting back.

The plan is something right out of Robert Moses’ 1950s designs: Draw bigger and wider roads everywhere, at even spacing, and design completely around the needs of cars to the exclusion of people.

My grandparents used to live in South Florida (like so many others), where the entire landscape is filled with a grid of six-lane highways surrounding country clubs and housing subdivisions.

It’s not a pleasant urban form, and is certainly not walkable or bikeable. It’s not what Loudoun should aspire to look like.

Sadly, that’s exactly what this plan envisions for Loudoun. Ashburn would become crisscrossed with six-lane expressways, between several freeways. The plan also calls for massive circumferential car capacity between Loudoun and Prince William County, despite the fact that current congestion is east-west, not north-south.

Eastern Loudoun roads in the Countywide Transportation Plan.

Teal roads will become 6 lanes, brown 8, red 10. Freeways are in yellow.

Loudoun planners, like so many others, just plugged their county into traffic modeling programs and out popped a set of road widenings. The basis of this is model is the MWCOG TPB model, which is widely criticized for having numerous flaws. It works only moderately poorly on a regionwide level, but when narrowed down to a smaller area, its flaws get magnified.

Skeptical residents hired Smart Mobility to evaluate the plan. They write,

The approach used in the CTP is one that has led our nation to spend exorbitantly on roadway construction, with the primary results being costly road improvements, induced traffic, and persistent congestion. The plan states that this approach is “industry accepted.” This may have been true twenty years ago, but the CTP approach does not represent the current practice for multimodal transportation planning.

Transportation planners and engineers generally agree that this type of conventional application of a travel demand model is not appropriate for regions that are seeking to reduce traffic congestion by implementing compact, mixed land uses and street networks that provide options and ease traffic.

Smart Mobility found that the model is only about 74% accurate, and overstates the north-south travel demand by 33%. The model also assumes gas prices will remain low, which is unlikely.

In addition, Loudoun County interpreted the model in an entirely car-centric way. When roads showed up as congested in the future, they assumed the solution was to widen them. This flies in the face of the county’s own Comprehensive Plan, which calls for reducing traffic through more compact and walkable development, not increasing it by paving more and more of the county.

[T]he draft CTP states that “the computer modeling exercise for the CTP only considers road segments,” so it should be no surprise that the only solutions that arose from this modeling exercise was to widen road segments — with a total cost of $1.64 billion dollars.

In the real world, traffic capacity is constrained at intersections, and not on roadway segments. This is somewhat acknowledged in some of planning documents, which identify “choke points” on the region’s road network (see figure below). There are a wide variety of solutions to intersection congestion beyond simply adding lanes to roadways. In fact, adding lanes to roadways can make downstream congestion much worse.

Other solutions, such as increased street connectivity that allows drivers to avoid bottlenecks and provides alternative routes for short trip, or compact mixed use development that reduces trip lengths or allows some trips to be made by walking or biking, were not considered in the CTP analysis.

New Gilbert’s Corner roundabouts. Image by VDOT.

The new roundabouts at Gilbert’s Corner do a better job of alleviating traffic choke points than adding lanes. Development that creates a denser street grid, instead of pushing all traffic onto widely-spaced, heavily-congested arterials, better allows for growth without adding traffic.

Loudoun should follow the Smart Mobility recommendations and throw out its existing model. Instead, the county should identify more targeted road projects that focus on bottlenecks and access to areas slated for more compact growth in the Comprehensive Plan, not long-distance commutes that only exist in such numbers in the imaginary and inaccurate world of the COG/TPB model.

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.