By Eric Murphy
Modern state DOTs and their engineers are grappling with a different set of challenges than they did in the 20th century. Some are shifting to managing travel demand and limiting vehicle-miles traveled (VMT) to make their systems operate more efficiently. But engineering education programs may not be properly preparing engineers for these new challenges, sometimes leaving them to learn on the job in environments that can be mired in old ways of thinking.
A new review of engineering textbooks finds that none completely cover the concept of induced demand, leaving engineering students “unprepared” to understand the well-known phenomenon that has been studied for decades and is a grounding principle at many innovative DOTs. Induced demand typically refers to additional driving that happens when a road is widened: while the widening reduces congestion in the short term, that makes others seek out the less congested roadway, and the road fills back up with new traffic and congestion in just a few years. Meanwhile, DOTs have spent millions on new infrastructure that doesn’t deliver on its intended outcomes and adds to the agency’s maintenance bill.
The study shows one more way that engineering students may be unprepared, but the problem goes beyond textbooks, as we’ve written previously. The authors also note that induced demand is not included in the ASCE Body of Knowledge, which corresponds more closely to the practice of engineering in the field. While the authors’ interviews with professors found some do incorporate the concept, transportation engineers may be entering the industry improperly equipped to manage the modern problems that DOTs deal with.
In recent years, some DOTs have started moving away from the idea of accommodating driving demand by widening highways toward the idea of managing demand to better use the infrastructure that already exists. But engineers are four times as likely as planners to agree that road-widening reduces congestion, perhaps in part because of their academic preparation. The reviewed textbooks, say the study’s authors, tended to focus on accommodating travel demand and on how drivers avoid congestion—rather than on managing demand and emphasizing how drivers are attracted to free-flowing roads.
The authors noted
All seven textbooks reviewed here universally emphasized the “need” to “accommodate” vehicle demand, an ethos that appeared foundational to the textbooks. For example, the assumption that demand should be accommodated underpinned problems sets, for which students are asked to determine the number of lanes “required” or “necessary” to achieve a desired LOS [Level of Service]. Similarly, most textbooks included a statement about the ability of road widening to ease congestion, which is consistent with the idea that engineers should accommodate demand.
However, more DOTs are moving away from focusing only on building roads large enough to accommodate unlimited travel demand and instead are thinking critically about the strategies and infrastructure needed to manage demand. States like California, for example, have created induced travel calculators – and projects there are required to mitigate any additional driving they cause.
For these DOTs and for the next generation of transportation engineers, understanding the shifting role and modern problems that DOTs now grapple with is key for producing successful outcomes. That can start with how engineers are prepared to enter the field, and to that end, the authors of the textbook review study have created resources to teach the concept of induced demand.
Photo credit: Ethan Hooson on Unsplash. License.