Last week’s blog was about Smart Scale applications submitted in 2018, which have been recommended for funding. This week’s blog will cover those Smart Scale projects within the West Piedmont Planning District which have been funded during past rounds and are currently scheduled for funding via the State’s Six Year Improvement Program. As noted last week, Smart Scale is a relatively recent data-driven funding mechanism which ranks projects based on factors including safety, economic development, accessibility, congestion mitigation, and environmental impact; land use is another more
Roanoke County is tackling their first roundabout at the intersection of Colonial and Penn Forest, a $3 million undertaking to smooth out the flow of traffic. VDOT and the County are approaching this first experiment with a relatively old concept for safety reasons, but it’s worth looking at the role roundabouts can play in traffic flow in general and how they can impact things like air quality and fuel efficiency.
First off all, it’s important to note that small interruptions in the smooth flow of traffic can propgate out to enormous traffic delays. There’s even mathematical formula to prove it:
[M]athematicians from the Universities of Exeter, Bristol and Budapest…have developed a mathematical model to show the impact of unexpected events such as a lorry pulling out of its lane on a dual carriageway. Their model revealed that slowing down below a critical speed when reacting to such an event, a driver would force the car behind to slow down further and the next car back to reduce its speed further still.
The result of this is that several miles back, cars would finally grind to a halt, with drivers oblivious to the reason for their delay.
…Drivers and policy-makers have not previously known why jams like this occur, though many have put it down to the sheer volume of traffic. While this clearly plays a part in this new theory, the main issue is around the smoothness of traffic flow
(This math blog described the phenomenon as being similar to the waves emanating away from the center point of an explosion. Which, coincidentally enough, would be an excellent way to solve a traffic jam). I saw this principle at work in 2002 when a friend and I were in the middle of a cross-country road trip. We had spent the day in San Diego, visiting my old childhood haunting grounds, and were heading north to L.A. Somewhere in the Del Mar area traffic was at a standstill and we crept along at 5 miles an hour for a mile or two, wondering what horrific accident or construction project had essentially shut down the highway. Then we reached this magical points where everything just went back to normal, as if we had been trapped in a drawn-out Matrix fight scene and the film finally sped back up.
The culprit? A greenhouse on a nearby hillside had caught fire, and the aggregated effect of a handful of drivers slowing down to rubberneck brought several hundred cars to a screeching halt.
What goes for unexpected traffic delays also applies to transportation infrastructure that forces traffic delays. Roundabouts, along with other efforts like signal timing coordination (a huge issue, by the way, on the 419 corridor and one not easily solved as the corridor crosses three jurisdictional boundaries) do a better job at keeping traffic moving at a constant speed, thereby reducing the opportunity for traffic jams. The County’s experiment with the Colonial Avenue roundabout is a good first step in building smarter infrastructure to keep drivers moving efficiently.
Of course, you’re probably thinking, “But Roanoke doesn’t have traffic jams!” And, of course, you’re right (for the most part, though a roundabout isn’t the solution for the traffic delays along Elm and Shenandoah Avenues. But RIDE Solutions is nothing if not interested in the aggregated impact of incremental behavior changes, and those keeping cars moving at a constant speed may have little impact on our nearly nonexistant traffic jams, it does have some impact on our very real air quality problems.
Largely this is because vehicles are at their most inefficient when they stop and start, and therefore emissions are at their highest. Any effort that can be made, therefore, to keep cars moving at a consistent speed improves fuel efficiency and reduces air pollution. Of course, my preference would be to have the car off the road altogether, but barring that roundabouts are a good place to start building more efficient system.