How much can you save on gas by slowing down?

[00:00:00]I think everybody understands that slowing down driving slower, driving more smoothly does increase the efficiency in your vehicle. I think what's remarkable that you may not understand is if you multiply that across everybody on the road across the country per day and the numbers add up pretty quickly, pretty astronomically.

[00:00:27]Um let's bring in Professor Will Northrop who's a professor of mechanical engineering at the University of Minnesota.

[00:00:35]Will, thanks for being with us today.

[00:00:37]>> Great. Thank you for having me.

[00:00:38]>> Yeah, this was a research here. Let's see. Let me pull up my information here.

[00:00:43]Nationwide study um recently published in a peer-reviewed journal called Communications Sustainability.

[00:00:53]Um what's interesting is I think you know, I think people comprehend that if they drive slower and more smoothly that it does increase their fuel efficiency.

[00:01:02]What you looked at was really compiling these numbers across the country to look at daily savings and those daily numbers I found were uh kind of hard to believe really. It was in in incredible.

[00:01:20]>> Yeah, thank you. Yeah, that was the big surprise for us as well. You know, it's pretty well known that driving slower saves fuel and what we did was essentially analyze 120 million actual vehicle trips taken in 2025 2021 and found that for the average distance that people drive say on a commute around 20 minutes that the time saved by speeding is only around 54 seconds.

[00:01:47]However, if you take if you take the whole country and you you spread that out as you say and you say how much could we possibly save 2021 we showed that we could save 6.7 millions of gallons of fuel per day.

[00:02:01]>> Per day.

[00:02:02]>> Um, yeah, and close to about 22 million dollars of fuel cost.

[00:02:08]Uh, as you know, today's gas prices are quite uh a bit higher um and we're closing in on $4 per gallon.

[00:02:14]So, just looking at the analysis that we did would extrapolate that out to about 30 million dollars per day.

[00:02:21]>> Wow. And then 57,000 metric tons of carbon dioxide uh less released per day just by everybody driving the speed limit. Um, you look at that and it's interesting, but I mean what in what real world way then does this research then I mean impact anything? I mean, you're not going to necessarily convince everybody that just hey, drive the speed limit and look if we all did it, this is what would happen. I mean, what what is really the goal here, the outcome of this research?

[00:02:55]>> Yeah, that's a really good question, right? So, we're engineers. We're interested in finding out what the you know, what it really is about all about, right? So, we're not interested necessarily in trying to change people's behavior. I think we're just trying it with this paper especially we're trying to put out the magnitudes of what the savings could possibly be. You know, it's up to policy makers and others to determine what what actually would be done in um in the case of of speeding. I know it's a it's something that is taken for granted by most people that most people want to do it, right? So, I don't know if we're going to be able to change people's behavior, but really I think just understanding the the impact of speeding on the use of fuel is something that is important for society to know.

[00:03:37]>> Yeah, have you did is part of your research whether it's this or other projects? Have you looked at the history of the speed limit in the US? It was in the early to mid 70s when the speed limit was reduced across the country to 55 mph. So, that 55 mph speed limit, which then manufacturers actually put a mark on the speedometers where 55 was, that was part of the requirements as well. That was an effort to combat the the, you know, energy crisis of the '70s.

[00:04:11]>> That's right. It was the I mean, I we didn't do a deep dive into history, but clearly the in 1973 uh they passed the emergency highway um energy conservation act.

[00:04:22]And that that act set, as you said uh rightly, set the speed limit to 55 mph on the highways. That wasn't a random number, either.

[00:04:31]What we what we find is that the 55 mark in our research is not the only to find this, but the that that 55 mark is an optimum speed for smooth driving on the highway or optimum driving for terms of fuel economy.

[00:04:45]Driving slower than that essentially has a has actually more of a penalty on time, disproportionate uh penalty on time as well as traffic flow.

[00:04:55]And going faster than that tends to have a exponential effect on fuel. So, 55 wasn't an accident. Uh since then in the 1990s, they the subsequently passed higher and higher speed limits, and now we have states that have speed limits around 80 mph or more, depending on, you know, the state.

[00:05:12]>> Yeah, and that was those those numbers were raised, I think they starting in the maybe late '80s. Um you know, certain [clears throat] roads were allowed to go up to 65 in certain areas with the with rural areas, the interstates, and then it just kept changing and changing as fuel costs seemed to go down in the in the that emergency, I guess, or that uh need or urgency for it had passed.

[00:05:37]Do you think there would be a realistic conversation anywhere about, you know, if there continues to be fuel cost concerns about lowering speed limits? It doesn't seem like it might be a realistic thing that I think lawmakers would want to tackle.

[00:05:54]>> Yeah, it doesn't seem it seems like a pretty charged issue to me based on my personal anecdotal experience on the highways as a driver who does drive the speed limit. Sorry for all your listeners out there who who are mad at me for driving the speed limit, but I I I tend to do that and I think that it's a very big ask, right?

[00:06:12]For people to do that. The perception of safe time, the perception of freedom I think is something that a lot of people in the US really cherish, right? This idea that that they have they're in control of their their own trajectory and what they want to do. So, I don't think it's going to be very easy to pass speed, you know, restriction.

[00:06:34]>> And we should point out your research isn't advocating for lowering the speed limits. Your research was looking at literally driving the current speed limits as they stand.

[00:06:42]>> Correct, as they stand, right? So, we weren't even looking at say Nevada lowering speed limit from 80 down to 65, you know, we didn't even look at that that impact.

[00:06:52]What is interesting though in places like Nevada, not to call that state out in particular, but places that have high speed limits, it turns out that they actually have a really high rate of speeding even above their speed limit.

[00:07:04]So, raising [clears throat] the speed limit doesn't necessarily mean that they drive within that limit. It just means that they go even faster.

[00:07:09]>> Even faster.

[00:07:10]>> Yeah, so yeah, I'm not really sure how to reconcile the problem.

[00:07:16]I want to point out though what we're doing doing and showing here is fairly technology agnostic, right? So, it doesn't, you know, we're not advocating for a technology change or anything to to to to change essentially the the main restriction, the main cause of this whole thing is the aerodynamic drag that exists on the outside of a vehicle goes up with the square, you know, the square power of the of the speed and the and the power or the fuel consumption goes up with the cube root or the cube of the speed. So, it actually just goes up exponentially as you get higher. So, no matter whether you're driving an EV, a hybrid, a an engine power car, it it these physics still apply.

[00:07:59]>> All right. Will Northrup, professor of mechanical engineering at the University of Minnesota, thanks for the time today.

[00:08:05]>> Great. Thank you so much for having me.

[00:08:06]>> You bet.