KXAN Austin

UT expert explains how induced demand could impact I-35 project’s congestion relief

AUSTIN (KXAN) — As the Texas Department of Transportation collects feedback from residents on its proposed I-35 Capital Express Central Project, agency officials say the proposed highway expansion will relieve congestion levels along the interstate.

But some transportation experts forewarn of induced demand, adding I-35 might not see the kind of relief officials anticipate.

“Induced demand is very much like latent demand: If you lower the price of something, there are people waiting to buy it — you just have to hit their strike price,” said Kara Kockelman, a professor of transportation engineering at the University of Texas at Austin.

In relation to highway projects, Kockelman said roadway improvements can lead to changed driver behavior. People might begin to shift driving habits and choose destinations further away, or travel during what used to be peak traffic times because congestion has eased.

However, Kockelman said when that happens, this initial ease in congestion volumes makes the corridor more attractive — enticing more people to drive on it and, as a result, increasing traffic loads that can result in higher congestion levels yet again.

“By opening up I-35, what we do is increase the attractiveness of that corridor for longer distance travel,” she said. “As Texas grows and as Austin grows, and the construction period will be so long, there’ll be a lot of pent up demand just waiting to get onto that road when it fully opens.”

Induced demand is an issue other highways in places like Houston and California have historically seen, Kockelman said. With Central Texas’ continued growth patterns and development along the corridor, she said she anticipates congestion volumes will be almost immediate following the expansion of I-35.

“Induced demand is an old story, and I’ve seen this many times in Houston and California,” she said. “It takes about three to five years for those roadways to become congested again, but I think with I-35, the congestion will be right away just because the region continues to grow.”

With I-35 construction expected to begin in mid-2024 and run until 2033, Kockelman said the result could be headaches similar to I-35 construction efforts up in Waco.

“Just like we saw up in Waco with a much simpler expansion of I-35, you saw this sort of bottleneck rather crippling [I-35] many times a day for years,” she said. “And we will have that.”

One of the tactics used to mitigate congestion levels is implementing toll roads, such as SH 130. However, Texas leadership instructed TxDOT to not add more toll roads to the state’s footprint back in 2017, limiting that option.

In her opinion, Kockelman said a credit-based toll system would be the best strategy to minimize traffic volumes while maximizing use of alternative transit resources. Those credits could be reimbursed t drivers in the form of a travel credit to support mass transit use, bike rentals or rideshare trips.

But as for now, she anticipates the relief Central Texans are hoping for might not pan out in ways envisioned.

“I think it will be congested from day one at certain times of day,” she said. “But congestion is a form of a price — congestion is a rather inefficient way to allocate the scarce resource of road space.”