Induced Demand and the Rt. 7/287 Interchange

By Adam Stevenson

The Virginia Department of Transportation recently proposed improvements at the Rt. 7/287 interchange. The project scope “includes lengthened and widened ramps and expanded turn and through lanes along Rt. 287 between Eastgate Drive and the westbound Rt. 7 entrance/exit ramps.” It also includes “expanded pedestrian access to the W&OD Trail and traffic signal modifications.” 

These proposed “improvements” are a mixed bag. Expanded pedestrian access, if well-designed, would be welcome in this area. 

However, the widening of ramps and turn lanes runs counter to constructive placemaking. What I mean by that is that by making it easier for cars to travel through the town of Purcellville you, in effect, induce demand for these roadways. The effect of this increase in demand, after the roadways are widened and made more convenient for increased use, is that the stated goals of road widening remain unfulfilled. 

Our approach to cars, in the post-war era at least, has been based on an assumption that there is some sort of magic percentage of land that must be paved over to fit cars (both when stationary and when moving) and then we will somehow enter a car utopia where we can zip from point A to point B without a care in the world. 

In this “cartopia,” as it were, we have our cake and eat it, too. We have fun and vibrant communities, but we can leave them and enter them without a hint of traffic. Nothing seems further away from our lived reality. The truth is that there is likely not some fixed amount of cars that will traverse a certain area regardless of road conditions. 

We can induce (and reduce) demand for cars by how we accommodate cars. Folks will substitute personal car rides for bus rides, bike rides, walks, and ride shares when convenient. And these become relatively more convenient when movement by car starts to become relatively less convenient. Cars, as necessary as they are, have the potential to erode places by slow but persistent changes that widen roadways, expand parking lots and hollow out the places we call home–changing our “places to live” to “places to leave” (preferably by car).

The concept of induced demand not only has an effect on the quality of life of our town, it has a general effect on our localized efforts at minimizing carbon emissions to mitigate rapid climate change. 

Smart Growth America states it succinctly and clearly: “Even if we hit the most ambitious targets for changing our cars and trucks over to electric vehicles, we will fail to meaningfully reduce emissions from transportation without confronting this simple fact: new roads always produce new driving. This costly feedback loop referred to as “induced demand” is the invisible force short-circuiting the never-ending attempts to eliminate congestion by building or expanding roads.”

Instead of pouring money into wider roads that won’t and can’t solve the problem of congestion (as congestion is simply a feature of heavily used roadways when intensively used) we should encourage our elected leaders to enshrine the concept of induced demand into any new traffic study.

 This will ensure that any road widening or creation will be fiscally and environmentally responsible and responsive. This in turn will create a virtuous cycle. As congestion is treated as a complex problem (not a simple and non-dynamic problem to be quickly solved by newer and wider roads), we will look to a wider array of tools–concepts such as encouraging active transportation, improving and regularizing public transportation, and shifting toward mixed-use development patterns. And these tools are integral to constructive placemaking. While road-building necessarily shrinks place, these other methods can expand and deepen place. 

Furthermore, these three tools and methods mentioned as alternatives to default road widening and creation build off of each other in a mutualistic relationship. Active transportation (in other words, walking and biking) encourages mixed-use patterns of development as increased foot traffic induces traditional mixed-use methods of development (for a local example, see 21st Street). 

Relatively dense and mixed-use development can in turn stimulate demand for public transportation if these denser patterns of development place limits on parking and create the need for alternative methods of transportation. 

Adam Stevenson grew up in Purcellville and can be found many Saturdays walking around 21st Street with obligatory stops at Nichol’s Hardware and It’s Baazar’s LP collection. He’s particularly interested in sustainable urban planning and Loudoun’s flora and fauna.