Study: More SUVs on Minnesota roads are making traffic worse

NINA MOINI: I'm Nina Moini, you're listening to Minnesota Now and as always, we thank you for that. A new study has found that the increase in trucks and SUVs on the roads in Minnesota is making traffic worse. The study was co-authored by David Levinson, a professor of transport at the University of Sydney in Australia. Levinson previously worked at the University of Minnesota though for 10 years. He talked with Minnesota Now senior producer Aleesa Kuznetsov, about his research.

ALEESA KUZNETSOV: Why did you want to study this and what were you looking to find through this research?

DAVID LEVINSON: So there have been a few trends that have been noticed in the transport field related to trucks, and in particular the growing replacement of cars by small trucks. So most cars these days for the people use for personal travel are actually SUVs or pickup trucks or vans rather than the traditional car that we've been used to for ages. And this has been an increasing trend over the last couple of decades in particular.

People have noticed that their safety effects of this. So you have a larger vehicle and it's more massive. People inside of these vehicles feel that they're safer, and you are safer if you're inside the vehicle, but you're not safer if you're outside the vehicle. So that's been a problem.

People have, of course, noticed for a long time that there's fuel economy issues with larger vehicles because it requires more energy to move mass, and these vehicles are heavier than cars are. But it's also been known for a long time that a truck is longer than a car, and a truck is bigger than a car. And I think we've known that since we've known about trucks and cars.

We've known that larger trucks take a longer distance to stop, and you need to leave a larger space, gap between your vehicle. If you're driving a truck and vehicles in front of you so that you can safely stop and that vehicle is behind you because you're so big will tend to give you more space. Now, this has an implication on traffic levels and no one's really systematically looked at that before.

Now, the great thing about Minnesota, which I learned when I was there, but it was really reinforced to me after I left was that Minnesota's got the best traffic data in the US. And they've been collecting data at loop detectors, magnets that are placed in the road and that record every time a vehicle goes over them. So every section and every lane of the freeway system in Minnesota has these detectors and they've been tracking this since the 1990s.

So this is a long term set of data, which doesn't really exist anywhere else as comprehensively. And it occurred to me we could look at, well, what has been happening to capacity? So every time you buy a larger car, the number of cars that the freeway can move goes down.

And we wanted to see if we could see this in the traffic data. There's a set of special detector stations. Those stations measure the number of trucks that are going through. And we can see at those stations exactly the number of vehicles by type that are going through. And we could look at the flow at those stations and what's the maximum flow at the time when those stations are congested.

And we can see that that's been going down and that's been going down proportional to the number of large vehicles that are there. So we can see that the number of trucks is decreasing the capacity of the system. And our freeway system is thus moving fewer vehicles than it did 30 years ago.

ALEESA KUZNETSOV: So you found that there's more SUVs there taking up more space. What does that mean for traffic? Does that mean when there's rush hour cars are moving slower, or what are people seeing when they're on the road now that we didn't see 20 years ago?

DAVID LEVINSON: So there was certainly congestion 20 years ago, and some of the roads have been expanded. But the number of vehicles it takes to reach a congested level of traffic is fewer, and so you're more likely to see congestion for the same number of people traveling because people are in SUVs and vans and pickup trucks, but especially SUVs.

I mean, the number of SUVs has gone from a few hundred thousand to almost 2 million by 2019 in Minnesota. So every one of them is a little bit longer than an automobile and a little bit heavier than an automobile. So they have a little bit longer gap. So we're using more space for each car and that just means we can move fewer cars or trucks.

And this matters, especially during peak times. In off peak times, it's not really a critical issue, but during peak times, the peaks will last a little bit longer because there'll be congestion and they will extend for a longer distance. So the queues on the freeway, the backups on the freeway, the queues at traffic lights will all be longer than they otherwise would have been.

ALEESA KUZNETSOV: So you mentioned lane expansions, but is there something that MnDOT or other state agencies can do to help with this now that this has seemingly the new normal, like we're just going to have more trucks on the road? Is there anything that can be done to help alleviate this extra pressure it's added?

DAVID LEVINSON: Well, I mean, I think from first principles, the thing you ought to be doing is trying to discourage this. So you don't want there to be more trucks on the road. We're using more energy and more material to move the same number of people as we used to. And this is just growing inefficiency.

You can look at almost every other technology. It's gotten smaller over time. The size a car phone in the early 1990s versus the size of a smartphone today. And yet cars, I mean, people may or may not have changed significantly in size over the last 30 years, but they haven't changed as much as the size of their cars have. And I think that's the first problem.

And the question is, how do you deal with that? And none of this is going to be popular, but you could look at making sure that the taxes and charges that are paid for by truck owners are higher than would be paid for by somebody who's using an automobile. So you could have emissions taxes that are proportional to the amount of pollution that's generated.

Electric trucks will take up just as much space as internal combustion engine trucks or diesel trucks, but we'll still have a greater level of emissions. You could talk about registration fees being even higher for trucks than for cars, but putting the genie back in the bottle is going to be a slow process. You still have all of these cars and trucks that are on the road now, and they're not going to go off the road, and they're particularly not going to go off the road if tariffs on new vehicles go up. People will be holding on to their vehicles for much longer.

So the question of can you manage the road better for trucks than you've been doing? And it's not easy. I mean, all of the standard things that Minnesota DOT has been doing to try to make traffic move more smoothly applies for cars and trucks. And unless you're willing to discourage trucks in the first place, this is something that you're going to be stuck with.

ALEESA KUZNETSOV: What do you hope your data can be used for? Who do you hope looks at this and considers this or maybe is it already being shared with people like MnDOT?

DAVID LEVINSON: Aside from science being good for the sake of science, one hope's that, that there's information here that will lead to what I would think of as appropriate pricing and regulation of different types of vehicles. We underprice roads in general. And as a result of underpricing roads, we overconsume them.

So if you look at what share of the costs of roads are paid for by users of roads, and it's well less than 100% and the rest is paid for by taxpayers in general, many of whom, of course, are road users, but they're not paying for it proportional to the amount of cost they're imposing on the system.

And ideally, we would have a system where people paid for the amount of cost they imposed on the system, like when you're purchasing any other normal good you're paying for the actual cost of that good. It's not generally being subsidized by the public. When things are subsidized, we consume too much of it, and when we consume too much of it, we're wasting resources.

ALEESA KUZNETSOV: So would you advocate for tolls?

DAVID LEVINSON: I think we should have a systematic road pricing system, I mean, I think we eventually will. Having toll roads everywhere where, I mean, the thing that people in Minnesota imagine was stopping on the Illinois Turnpike thruway and paying tolls every couple of miles. And that's really inefficient.

But we can have a road pricing system where we charge more during the peak and have discounts in the off peak, so we don't have as much travel in the peak. I mean, people think about, well, I don't have a choice, I have to travel in the peak because I'm going to work or I'm going home. And you may be doing that, but lots of people are traveling in the peak who aren't going to work and some people have flexibility.

And if they saw different prices during the peak, in the off peak, they would choose to travel during the off peak. And we would have different prices for different sized vehicles based on how much damage they're doing to the road and how much capacity they're using up, so larger vehicles would pay more than smaller vehicles. And pavement damage and for safety costs and so on.

And I think this road pricing system, in some ways it's inevitable as we move towards electric vehicles. But this is going to take a couple of decades to convert the fleet over to electric vehicles because we're no longer going to be paying fuel taxes once you have electric cars as comprising the bulk of the fleet. But this is going to take a while and I think if we can get ahead of this, that would be good public policy.

And the question of how electric vehicles pay for their use of the roads, I think is something that hasn't been fully resolved. But if they pay on a per mile basis and they have a discount for traveling in the off peak versus the peak, I think you're halfway there.

ALEESA KUZNETSOV: Well, David, thank you so much for sharing all this research with us. Appreciate your time.

DAVID LEVINSON: Thank you.

NINA MOINI: That was Minnesota Now senior producer Aleesa Kuznetsov talking with Professor David Levinson.