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Surprise! Americans drive the speed limit — unless they’re on I-15

January 21, 2010

Here’s some interesting research that challenges the conventional wisdom about travel in America: U.S. motorist do drive the speed limit — unless they’re on I-15 in Nevada and Utah, better known as “America’s Autobahn.” That’s according to a survey released this morning by TomTom, a manufacturer of navigation systems.

The results were calculated using data from TomTom’s Speed Profiles, the historical speed database from the company’s Tele Atlas map business. Among some of the other findings, TomTom concluded that the slowest roads in the nation were in Washington, D.C.


Data was organized to show the average speeds on interstate highways and to reflect only free-flow speed data, or average speeds when there is no traffic present. When compared to a database of posted speed limits, the results indicate that the average U.S. driver stays within the speed limit range on most urban and rural interstate highways.

Mississippi is fastest. Across all interstate highways, Mississippi has the fastest roads, with average speeds of just over 70 m.p.h and posted speed limits ranging from 65 to 70 m.p.h. New Mexico (70 m.p.h actual average, 70 to 75 m.p.h posted speed limits), Idaho (70 m.p.h actual average, 65 to 75 m.p.h posted speed limits), Utah (70 m.p.h actual average, 65 to 75 m.p.h posted speed limits) and Alabama (70 m.p.h actual average, 60 to 70 m.p.h posted speed limits), round out the top five states with the fastest interstates in the country.

America’s Autobahn. Our fastest road is on I-15 in Utah and Nevada, with speeds averaging 77.67 m.p.h, although some spots on that highway allow 80 m.p.h.

Middle America speedway. The nation’s fastest area is in the middle part of the country. Seven of the top 15 states with the fastest highways are in that area. The average speeds on roads in Mississippi, Nebraska, Kansas, Iowa, Idaho, Alabama and Missouri exceed 67 m.p.h; the average posted speed limits in those states is 70 m.p.h.

D.C. is slowest. The nation’s capital has the slowest average speed on its interstate highways, at 46 m.p.h. After Washington, the states with the slowest interstate average speed are Hawaii (53 m.p.h), Delaware (61 m.p.h), Rhode Island (63 m.p.h), and Oregon (63 m.p.h).

(Photo: dirkoneill/Flickr Creative Commons)

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34 comments

  • Texas Observer

    I find it hard to believe that Texas wasn’t on their list with average speeds over 80 mph. It should be noted every street and highway is an autobahn to Texan drivers including school zones.

  • http://icandrive55.blogspot.com/ David

    I don’t buy it. I have been driving the speed limit for a couple of months (http://icandrive55.blogspot.com/), and I am passed by just about everyone. It is not as bad on highways as it is on side streets, but I rarely see anyone driving the speed limit.

  • John M

    This seems a little odd to me, how can Americans be driving at the speed limit, except in Utah and Nevada, when your article states that Mississippi is the fastest state with an average speed of “just over 70mph” and the maximum speed limit is 70. To have an average higher than the speed limit means that folks are speeding.

    I agree that if you drive in Utah, Nevada, Wyoming, Montana, you will see people flying down the highway and it isn’t just on I-15. Take I-80 from Laramie WY. to Reno NV. and you can cruise at 80mph most of the way. You will need to slow down around Salt Lake City, not because the speed limit is strictly enforced but because the traffic gets heavy.

  • Ron

    Obviously, TomTom doesn’t get used on I-95 between Virginia and Florida where people think 95 is the speed limit not the interstate number. If you drive anywhere near the speed limit you are going to get run over.

  • Mike

    I had no doubt that the midwest states would be the fastest. Nothing to see driving through and you just want to get to your destination as fast as possible. Surprised Michigan isn’t up there. Driving through, I can be doing 70 and get passed by everyone, even Amish buggies!! LOL

    Interestingly enough, with safer cars and brake systems there appears to be less of a correlation with raising speed limits and deaths like there used to be. Lets hope the remaining states with lower speed limits raise theirs and get with the program.

  • MeanMeosh

    I have to call BS on this study. The problem is, they’re using average speeds, which tend to be unreliable. If 100 cars in the left lane are driving 90, and 100 in the right lane are driving 50, you’d end up with an average speed of 70, but that doesn’t mean people aren’t exceeding the speed limit (head down I-75 in Florida sometime, and you’ll see this exact example).

  • Jonathan

    Does anyone else have problems with TomTom collecting this data in the first place?

  • tim

    Average speed includes rush hour(s), which in DC lasts from 6am-11am, and 3pm-9pm. Then the average speed on I-66 or I-495 tend to be about 25 mph. The average speed on I-66 and I-495 outside of rush hour is probably about 70mph. There are always outliers.

    It doesn’t surprise me that the fastest areas tend to be the less congested areas that have longer wider roads, like in the midwest.

    Here in the DC area, the roads that were designed to move 1.5-2million people are now transporting about 4-4.5million people.

  • y_p_w

    TomTom claims that the data is collected anonymously and collected with the Tele Atlas service that distributes updated maps. I suppose if one doesn’t trust the anonymity then the service can be refused.

    I’d note that if you live in the San Francisco Bay Area, the estimated time to a destination is collected by quietly sampling FasTrak toll collection transponders at several checkpoints and averaging the times to destinations – probably throwing out samples that appear like someone stopping too long along the way. It’s also the basis for the congestion calculations for the 511.org system. Anyone who doesn’t trust this can put their transponder in a metalized mylar bag. They claim that the ID data is scrambled first and the encrypted ID database is deleted every day.

  • Daniel

    I would like to see demographics of Tom Tom’s users (who they collected the information from). My guess is that teenagers, and younger drivers in general, are less represented in this survey; yet make up a larger portion of fast drivers.

  • Brian

    The road leading to Sedona has one of the fastest I’ve seen. The posted speed limit is 75 mph. I believe I may seen drivers go at almost 90 mph on that highway.

  • Wrona

    I think the reason Texas isn’t among the fastest is that you have several major cities, Dallas and Houston specifically, that are like parking lots during rush hour (which lasts from 3am to 10pm).

  • http://www.roamingtales.com Caitlin

    I think the methodology is flawed. If people really stuck to the posted speed limit, the average speed would be slower than the speed limit. The speed limit would be the maximum speed and the average would be lowered by all the times when traffic or weather conditions slow you down.

    On 101 south of San Francisco the speed limit is never more than 65mph (and sometimes less), but the flow of traffic is usually 70-75mph, even 80mph.

  • Justin

    @ Wrona and Texas

    Houston and the surrounding areas are parking lots during rush. Takes hours to go a few miles. Still, whenever speed can be achieved (off peak), people in their pick up trucks figure move it or lose it. Guess you can take the redneck out of the country, but that doesn’t mean they act any different. Texas drivers have no qualms about making it known they are aggressive and suck at driving.

    As per Michigan, driving in Detroit is something in its own right. I’m amazed Ohio isn’t up there. Hell I-70 and I-75 are always moving along fast unless during rush or an accident.

  • Cynthia

    Heh . . . but average speeds do not tell the complete story.

    I challenge anyone to show that drivers on the freeways in the SF Bay Area go the speed limit or lower when the traffic is not backed up. Additionally I recently drove from SF to Phoenix via I-5 and I-10 and was almost continually tailgated and passed despite being 5 mph over the speed limit myself.

    All averages do is normalize the spread between the extremes . . . they don’t show the reality on the road.

  • y_p_w

    Guys – read the text again. They tried to calculate average speeds that reflected “free flow” periods. All the talk about rush hour doesn’t apply to their study.

    As for crazy stuff, try taking a taxi in Bangkok. I remember a taxi being stuck for 15 minutes literally not moving at all. Then all of a sudden there’s room to move and the driver guns it to about 50 MPH for a couple of city blocks until the driver then slams on the brakes as traffic backs up again.

  • http://www.roamingtales.com Caitlin

    @Cynthia I learnt to drive in the SF Bay Area last year. My driving instructor was very firm that I should go with the flow of traffic rather than the posted speed limit on the freeways. He said it was unsafe to have people passing me and made me speed up. He also said that the police are looking for unusual behaviour and won’t book you if you are going at the same speed as everyone else, but might if you’re going slower because you stand out, and that if they do book you, you can argue that in court.

  • Mary H

    Visiting Houston, I was impressed at the distance drivers keep between moving vehicles. The traffic flowed well and I felt safer than I do in Charlotte, NC, where tailgating rules. But still don’t like driving in Houston. Not enough signs on the freeway. Only one per exit seems the norm. Too little time to change lanes. Caitlin makes a good point. Driving at the speed limit in Houston seemed to challenge folks to get past me in a hurry. So next time, I’ll go with the flow. And hope I don’t miss too many exits! LOL

  • jerryatric

    Obviously this writer has NOT driven S. California’s I 5 OR 10.
    I recently drove down 5 @ 80 & was passed about 4 times. This is from Redding to L.A.
    On 10, exiting @ about 75MPH some guy passes me on the inside exit lane going straight. I estimated his speed – in excess of 90 MPH.
    It seems they not only speed, but are very reckless. I drive through this long corridor every year & no one drives the speed limit. They tailgate & when there is an accident – they have to close the Interstate because it’s so bad.

  • Philip

    I am distressed that all the comments above do not even mention the economy factor. I drive to class twice a week, fifteen miles. I set my cruise control at the speed limit of 55mph; 90% of cars whiz past me. Many dangerously cutting in front of me. My car is rated at 21mpg; I have gotten up to 29mpg. Also note that when the speed limit was 55mph, the number of deaths were far lower than now.
    The number of car deaths and maiming, does not seem to be significant in comparison to getting somewhere fifteen minutes earlier; and what do you do with the fifteen minutes you ‘save?’ People bitch and moan about the price of gas. Driving slower saves gas and forces the oil producing nations to dramatically drop the price of oil. And the life you save can be your own or a loved family member or friend; or other innocent driver. Everyone needs to be responsible!!

  • Jasper

    In this kind of measurements the “average” doesn’t mean that much. You would have to look at the distribution of the speeds. I bet that you’d see a slight peak around speed limit -10 and one around +10.

    On the other hand, I will admit that most of the speeding I see is around large cities (DC, NY, Chicago, LA). I guess that folks are happy to drive fast for the few hours a day it’s possible. I have also noted that the further you get from big cities, the more people stick to the speed limits. On the other hand, speed limits tend to be higher in rural stretches than around cities.

    FYI: Yesterday around 11am the mixing bowl in DC/NOVA (I-95/I-495) was stuck in both directions.

    BTW: Delaware’s exception does not surprise me. DE does not have much interstate to start with, and then they put a nice toll booth in the middle of it. Pretty much the same goes for HI and RI.

  • Joe

    @Philip, any fatality increase is only because of total population. See http://www-fars.nhtsa.dot.gov/Main/index.aspx; the per capita fatality rate has consistently declined every year since 1997 even as freeway speed limits have increased.

    Caitlin’s driving instructor was correct. Numerous reputable studies show differences in speed between vehicles, rather than actual speed, to be one of the key contributing factors to accidents. Just google “speed variance.” You might consider which motorist is driving more safely: The one traveling the posted speed limit who forces those around him to slam their brakes, switch lanes, etc., or the person who drives 10 mph faster but doesn’t force anyone else to alter their normal driving behavior.

  • DN

    Hawaii’s freeway speed limit is 50 – 55mph, and the one that’s at 50 hasn’t changed in over 3 decades. It is one of the few states that does have a minimum speed limit posted right underneath the maximum speed limit (40mph) that I’m aware of.

  • David Farnham

    These people obviously haven’t friven I-5 between LA and San Diego, where even loaded trucks routinely do 80+.

  • http://www.tomtom.com Kevin Carter

    I am writing on behalf of TomTom and Tele Atlas. I would like to stress the point that we collect GPS data anonymously, and only on an opt-in basis. We don’t track individuals. Rather, collective data helps us steer people clear of traffic hot spots and recommend the most efficient routes.

  • http://www.angrymarks.com/ Kevin Fields

    I’m not surprised that the average is around the posted speed limit. Since gas prices went sky-high a few years ago a lot of drivers – especially commercial drivers – have slowed their speed in order to optimize fuel efficiency . And as the semi trucks stick to 55 MPH (some of them w/ governors in their engines) I tailgate right behind them, picking up their slipstream and gaining an extra 5 MPG myself. :-)

  • Philip

    Thanks, Joe, for your link to the number of fatalities showing a decrease of crash deaths at 2000 lower (’94 to ’08). Should I be gratified that ‘only’ 32,000 people died? I hope one of them, Joe, was not a family member or friend of yours.
    I know I am being facetious, but you seem to take a jaundiced view of people
    dying on the roads. When the national speed limit was 55mph, the number of fatalities decreased dramatically.
    Speed kills, Joe. SPEED KILLS !!

  • http://www.roamingtales.com Caitlin

    The attitude to speeding does seem to be very different in the US to in my native Australia. Numerous government driving campaigns have targeted drink driving (“if you drink and drive, you’re a bloody idiot”), speeding, and stopping to rest after long periods of driving (“stop, revive, survive”). The campaigns are very graphic and the speeding ads in particular liken people who speed with men who have small penis complexes (I’m not kidding – this is a government campaign).

    See: http://www.youtube.com/watch?v=c2nvAFOk7x0
    http://www.youtube.com/watch?v=75GuzsGzoP0
    http://www.youtube.com/watch?v=ZbaTy2RYhe0

    These are all recent ads but the no-holds-barred graphic ads have been going for at least 20 years (since I was a kid). And they’re damn effective. Australia has a population of 20 million and it makes the news when the national road toll makes double figures for the year.

  • Brad

    This article’s conclusion isn’t backed up by the data it cites. If a speed limit is set correctly (rather than to raise revenue), it will be at no less than the 85th percentile speed, rounded up to the nearest legal speed limit (increments of 5 mph or 10 km/h). A speed limit that corresponds to the average speed of travel, assuming we’re talking about the median and not the mean, is the 50th percentile. (If the cited average is the mean, then the speed limit would be set even more ridiculously than that number would indicate.)

  • Pingback: If New Mexico were to introduce 80 mph speed limits... - (NM) - Page 2 - City-Data Forum

  • Mekhong Kurt, Bangkok, Thailand

    y_p_w — I smiled in recognition, as I’ve lived in Bangkok for days shy of 16 years, always in the area along Sukhumvit between Soi Asoke and Soi Thonglor. I’ve had some “exciting” moments in taxis and buses, and on motorcycle taxis, over the years, THAT’S for sure!

  • Carlo

    I wonder how this compares to data from ca. 1995 – just before the national speed limit was repealed. I remember the big argument back then was “if people drive 70 now, when the speed limit is 55, how fast will they drive when the speed limit is 70?” In my experience, it appears the answer is 72.

    Someone earlier said something about setting a speed limit properly and that formula actually comes from studies that show people drive at speeds that are comfortable and safe. People inherently know how fast to drive under normal conditions. Of course, there are always individual idiots, more of them than we like to see, as well as special circumstances like weather conditions, but the general observation is true.

    I too find it odd that Texas didn’t make the list, given that stretch of I-10 in West Texas that has a speed limit of 80. But maybe it’s because so much of Texas’ population (and interestates) is concentrated along the I-35 corridor. I will say, however, that it’s that area of the state that has far more than it’s share of idiots who drive not only much faster than the speed limit, but also much faster than the flow of general traffic.

  • Tom

    Explain again why they have interstate highways in Hawaii.

  • http://fashionlove.net/bop-nam bop nam

    Last week I talked about how fast is fast enough,
    and that one of the easiest ways to save fuel was by simply going
    slower. Well rejoice! Apparently all of America heeded my advice, and
    American drivers, on average, drive below the posted speed limit.

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