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The Utah Department of Transportation has models showing that widening Interstate 15 through the northern counties of Salt Lake and southern Davis will reduce projected travel times by half a decade in the future.
But widening freeways is “clearly” not improving congestion, said Susan Handy, professor of environmental science and policy at the University of California Davis.
Handy is an author and co-author of Policy Briefs, which summarizes research and studies on induced demand: the idea that the expansion of freeways leads to a proportionate increase in vehicles using the road.
The explanation for this is fairly simple, Handy said. Widening the highway will reduce travel time costs, and people will consume more when those costs decrease.
A wider highway serves its purpose, which is to carry more cars, she said. The declared goal of reducing traffic jams will not be achieved in the long term, she said.
It’s not clear if there’s actually a solution to congestion, Handy added, but it’s easier to live with if authorities allow people to avoid congestion by investing in high-quality, high-frequency transit services.
“It’s really about rethinking our communities to make them less dependent on all this driving,” Handy said.
In the western neighborhoods of Salt Lake City—from Rose Park to Fairpark to Glendale—there is growing opposition to I-15 expansion plans. And in a Salt Lake Tribune editorial last week, Mayor Erin Mendenhall called for tough questions and analysis about more freeways. “History has shown that if you build more, more will come,” wrote Mendenhall.
The Utah Department of Transportation is exploring a holistic approach to transportation within the corridor between Farmington’s Shepard Lane and Salt Lake City’s 400 South, spokesman John Gleason said.
“The expansion of I-15 is part of a comprehensive approach to meeting transportation demand by 2050 that includes additional capacity for FrontRunners, additional bus services, local and regional road improvements, and new facilities for those who walk and bike ‘ Gleason wrote in an email.
He added that the state agency believes the currently preferred option of widening the freeway along the 17-mile stretch is a balance between traffic improvement and community impact.
Utah’s growing population and aging infrastructure make it necessary to look for ways to improve mobility, Gleason said. That included expanding capacity to meet rising demand, he said.
Based on a 2019 study, driving from Farmington to Salt Lake City along I-15 takes about 18 minutes at peak morning hours compared to 19 minutes in the evening.
According to Gleason, considering future growth travel models, it will take UDOT more than an hour to travel the same stretch of highway in 2050.
In representations of the country, travel times of 55 minutes are expected during the morning peak hours and 66 minutes in the evening.
Implementing UDOT’s preferred option of adding five general-purpose lanes, one fast lane and one auxiliary lane in designated areas in each direction results in a projected travel time of 30 minutes, Gleason said.
According to a presentation, it would take 28 minutes to get from Farmington to Salt Lake City during the morning rush hour and 30 minutes to drive back north in the evening.
“While this still represents an increase in travel time compared to today, we believe this is the most balanced travel improvement with an impact on the surrounding community,” Gleason wrote.
A second option would be similar, but would make the central express lanes reversible to serve morning and evening traffic needs. According to the UDOT presentation, this would reduce morning travel time to 21 minutes and evening travel time to 22 minutes.
But study after study has shown that while widening highways initially reduces travel times, traffic increases again when people change their behavior.
When commuters learn that there is less traffic on the freeway, they may switch from public transport to cars or change their route to work. Over time, people may move further away from work and developments may become more scattered in response to capacity expansion.
A 2015 policy brief from UC-Davis’ Handy showed that a 10% increase in capacity would likely increase traffic by 3% to 6% in the short term and 6% to 10% in the long term.
In a recent policy brief that Handy co-wrote, that figure was up to 3% to 8% in the short term and 8% to 10% in the long term.
People have observed and experienced this for decades, she said. Officials have continued to widen the freeways, she said, but congestion is still as bad as ever.
The projections from the transportation departments are wrong, she said, and flawed to begin with.
A lot can happen between now and 2050, including changes in technology, society and development patterns, Handy said.
“There are forecasts based on many assumptions. Talking about this far into the future, there’s a lot we just don’t know.”
UDOT is responsible for driving changes in travel behavior over the coming decades — such as switching to other types of travel as they improve, Gleason said.
Nevertheless, according to Handy, forecasts are not suitable for predicting the increase in car traffic that will result from a wider freeway. They tend to overestimate the benefits while underestimating the environmental impact.
Congestion often corrects itself, she added, because people have an incentive to drive less when traffic increases. Forecasts don’t take that into account either, she said.
A graduate student at UC Davis is studying why officials keep widening the freeways, Handy said.
There are many different reasons, but two stand out, she said: Expanding freeways is the solution that transport authorities have exploited since the 1960s, and many people have a financial interest in the approach.
UDOT and similar departments in other states used to be highway agencies, Handy said.
“They were founded with a mission to build highways and have only expanded their mission in recent years. Motorways still make up the bulk of their activity.”
Motorists are also demanding wider highways because they don’t fully understand the induced demand, she said, and policymakers are ready to cater to voters’ wishes.
It was not clear whether the officials could fix the traffic jam, Handy said.
But if they really want to reduce the number of vehicles on the road, pricing is needed, she said.
This does not simply mean setting up an expressway on which car pools are formed or a toll is paid.
“It would require a toll for the entire road,” Handy said. “People drive as much as they are because we undervalue driving relative to its impact.”
Toll roads are not politically feasible — particularly in the West — but ultimately may be the only thing that makes sense, she said.
People need to discuss whether congestion is a problem that needs solving, she said. Nobody likes it, and there are negative consequences for traffic, Handy said, but it’s sort of an inevitability of a vibrant city.
Congestion has only gone down during recessions and pandemics, she added, and maybe it’s time to learn to live with it.
Officials can help by making sure people don’t struggle with congestion, Handy said, whether it’s by letting people live closer to work or by improving public transportation.
Public transport needs to be of high quality, frequent and give people more options for the ‘last mile’ – the rest of their journey to and from work. This last-mile problem has burdened transit planning along the Wasatch Front for decades.
“It takes a very concerted effort, but the resources are there,” Handy said. “It depends on how we use the resources.”
Utah is considering a holistic approach that includes how to get people safely and easily to their final destination, whether by car, public transportation, bike or foot, Gleason said.
However, some states have begun to completely reconsider spending on highways and transportation, particularly in line with federal guidelines that encourage a “fix-first” approach before adding new highway miles.
Colorado, for example, passed a climate change ordinance in December 2021, urging transportation planners to redirect funding away from freeway expansion and toward vehicle pollution reduction projects, like buses and bike lanes.
This prompted government officials to approve updated long-term plans that abandon a major freeway widening project along Interstate 25 in Denver and reinvest more than $100 million in traffic and safety improvements.
Opposition from community and government officials led to the cancellation of a planned extension of Interstate 710 through Los Angeles. According to the New York Times, transportation officials dropped the project despite spending $60 million over two decades on design and planning.
Meanwhile, residents of Salt Lake City’s west side continue to question the viability of expanding I-15 at the expense of air quality and the possible destruction of homes to house the project. “It would be really nice if our resilience wasn’t tested this time around and maybe invested in our prosperity,” Salt Lake City City Council member Victoria Petro told The Tribune in January. Petro represents districts in the project area in the northwest of the city.
It’s not yet clear if their efforts will result in changes to the state’s plans, but Handy is siding with Westsiders fighting the project.
“The city will not crumble unless the road is widened,” she said.
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