Caltrans Admits Building Roads Induces More Driving, But Admitting a Problem Is Just the First Step

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Fifty lanes of traffic is not what we want. Image: Screenshot of a tweet from People’s Daily China this summer.

Eric Jaffe, in CityLab, recently reported that Caltrans “admitted” that expanding highways increases traffic by posting a policy brief on the subject of induced demand to its website. He called it a rare admission from a state department of transportation.

State DOTs, as the country’s road builders, have usually responded to congestion, and even safety concerns, by expanding and widening roads, expecting that more lanes will solve problems caused by too many people wanting to drive on them at the same time. But research has shown that making it easier and quicker for people to drive somewhere just encourages more driving. By linking to the policy brief, “Increasing Highway Capacity Unlikely to Reduce Congestion,” [PDF] Caltrans is openly acknowledging the connection between building new capacity and more driving.

But linking to a policy paper doesn’t mean that California will stop building roads altogether.

There is still plenty of pressure to keep building roads—from rural areas that want wider highways, for example, to local areas that tax themselves for new highway expansions (as Placer County is considering doing).

Meanwhile the State Transportation Improvement Program, which is the blueprint for investing in highways in California, contains locally preferred projects including highway expansions, and the California Transportation Commission continues to approve funding for them.

Streetsblog reached out to Steven Cliff, Caltrans’ assistant director of Sustainability, to find out whether the department really has come to accept the concept of induced demand–that if you build more highway miles, more miles will be driven. Cliff said, in short: yes. “It’s pretty settled science that capacity expansion induces demand,” he said. “We know that while it relieves traffic in the short term, there’s pent-up demand that suggests it just fills up again in short order. There’s ample evidence that if you lower costs, demand increases.”

And what does that mean for the department formerly known as the state highway department? (Under Caltrans’ new mission and vision, it’s now the department that “provides a safe, sustainable, integrated and efficient transportation system to enhance California’s economy and livability”–not just highways for cars.)

Caltrans, within its new strategic management plan, developed goals to reduce vehicle miles traveled (VMT). “We can’t keep using single occupancy vehicles as our primary way to get around,” said Cliff. “Arguably, we’re not moving people efficiently now,” he said, and it will only get worse as California’s population increases.

“Our focus has been on strategic expansion, and on expansion of the transportation system in ways that won’t increase VMT–or at least, not increase VMT at the same rate as population growth,” which the state projects will rise about 17 percent by 2030. Some capacity expansion will still be necessary, he said. “It just needs to be strategic.”

For example, rather than adding an all-purpose lane to a congested freeway, a carpool lane might be added, as was done recently on the 405 in Los Angeles. That project has incited complaints that it hasn’t reduced congestion—but that should come as no surprise to anyone who understands induced demand.

Stuart Cohen, executive director of TransForm, has spent a lot of time thinking about induced demand as well. “We know it exists,” he says. “That’s why we put up new transit routes—because we want to induce demand for transit. But we also know that new roadways induce more car trips.”

“We already have enough lane miles in California,” he pointed out. “We just need to use them better. If we had more than 1.2 people in every car and everyone wasn’t trying to use the lanes for the same few hours every day, we could avoid the vast majority of road widenings.”

In 2010, Caltrans developed a “Smart Mobility Framework” to help guide transportation planning in the state, although implementation has been slow. “The idea is to reduce demand first, by providing alternatives and incentives to driving alone, before you consider road expansion,” said Cohen.

TransForm has also developed the idea of the “optimized HOT lane,” which would allow both high-occupancy vehicles (HOVs) and toll-paying single driver cars to bypass congestion in an already existing lane. The revenue raised by the toll would be used to improve transit and encourage people to cut their driving by joining carpools and vanpools or using alternatives–not pay back bonds. The Bay Area’s Metropolitan Transportation Commission did a study [PDF] using the concept on the 101 corridor in San Mateo and came to the conclusion that more people could be moved with less money invested—with no road bonds needed for new construction.

The idea has the added benefit of addressing equity concerns by sharing some of the time savings with people who can’t afford to use the HOV lane.

Currently, however, it’s illegal to convert an existing lane to an HOV/HOT lane. Testing the idea on the ground would require a change in state law.

And getting policymakers to understand the concept of induced demand has been a challenge. “Intuitively, it makes sense that if we give people more space they’ll be able to move around more easily,” said Cliff. “But a lot of people don’t take it to the next level, where it means that more people will want to occupy the space.”

Caltrans, by posting the short paper on its website, is encouraging policymakers to think more deeply about the unintended consequences of expanding highways. Those who are interested in the topic and want to delve more deeply can access the research behind the brief, which was conducted by Susan Handy at UC Davis for the National Center for Sustainable Transportation and the Air Resources Board.

16 thoughts on Caltrans Admits Building Roads Induces More Driving, But Admitting a Problem Is Just the First Step

  1. I agree. I brought it up with CalBike, but pretty much crickets. We got as far as figuring out when it was passed and that’s it. They’re still digging, but it’s taking a long time.

    It probably won’t kill projects, just force them to follow the law and build the facilities. It’d be great to see more projects like the Denver-Boulder US-36 bikeway get built here in CA. Which, if I’m not mistaken, actually got built due to an environmental lawsuit or something of that nature.

  2. Oooh, good catch on the law. You should be able to kill a lot of noncompliant projects at the Draft EIS stage with section 887.8(b).

    More advocates in California need to know about this section.

  3. There’s a short discussion at the end of the UC Davis paper. do transportation and panning models consider traffic evaporation or do they have to model it indirectly by assuming certain mode shares?

  4. ≈ Caltrans has admitted this before sometime around 1990, except they didn’t have a website that the public could get at easily. Akos Szoboszlay of the Modern Transit Society, who was fighting freeway expansion and the Trojan Horse of HOT/HOV lanes in the San Jose area, dug that up in a paper document. Sadly, the same Caltrans who was aware of the futility of building and widening roads went ahead and built everything anyhow.

    Two admissions in 25 years just isn’t enough.

  5. The parallel concept is called “traffic evaporation” and there’s a whole body of literature on it, but it’s very hard for a lot of people to believe, particularly the people who come to public meetings to advocate for their own personal car.

  6. It’s not, but traffic studies don’t work they way. All projections always assume that everyone will drive, then the roads are designed around that projection. The big issue is that traffic studies never recommend anything beyond wider roads and more turn lanes at intersections. If they were to do that and set a standard that say any road that has 2 or more lanes per direction must include a dedicated transit lane in that direction and a separated bikeway, things would be a lot different and the alternatives would also function far different and would be much more efficient.

  7. One thing I don’t get… it seems like the idea of induced demand and its consequence, that you can’t build your way out of congestion, it well established. What about disappearing traffic – the idea that you can reduce capacity, whether by removing freeways or converting traffic lanes to transit or pedestrian space, without increasing congestion. Is it just less established as a concept? From an advocacy perspective it could be powerful. It could help defeat apocalyptic concerns about trading car space for sidewalks, transit lanes, and bike lanes.

  8. Pretty sure HOT/HOV lane conversions of general lanes are not just illegal under state, but also federal law. The Obama Administration had floated the potential of nixing that “experimentally” earlier this year as part of a highway bill, but I don’t think it’s made its way into the final piece of legislation working its way through Congress.

    As for the widening projects, local advocates just need to arm themselves with the CA Streets and Highways Code, which has a section (§887.8(b)) that has been in effect since 1994 requiring that all projects to increase capacity or safety must also provide a parallel path for nonmotorized travel. Somehow, that has thus far slipped past the good folks over at Caltrans and the regional transportation commissions; perhaps they need to be reminded. In either case, a lot of projects are out of compliance.

    Also, though they really should just be building them in tandem, Caltrans needs to ensure that as they undertake these widening projects, that they at least don’t impede other modes. Doing so creates a huge problem that then requires tens or hundreds of millions of dollars to remedy, thus pushing many alternative transportation projects into the realm of ineligibility on the basis of cost/benefit.

  9. “My name is Caltrans, and I am an autocentric.” Indeed admitting one has a problem is first; now let’s see some action.

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