Arkansas DOT accepts 75 mph request

After some delay Arkansas DOT acceded to a legislative request to raise the speed limit to 75. The speed limit proposal is open to comment by state residents (only) until December 13. Stripped of irrelevant material the 33 page speed limit report has five pages of content.

One graph says the average speed on rural interstates has been about 53 mph and the 85th percentile speed 71. Another gives the corresponding figures for urban freeways as 48 and 59. Rural multilane highways other than freeways fall in between. Rural two lane roads have 85th percentile speeds in the 60 to 65 mph range.

If these figures were accurate, the proposed 75 mph rural and 65 mph urban speed limits would be justified. The speed limit should be set so most drivers are legal. I don’t believe they are accurate.

On a typical American rural freeway the 85th percentile speed is 70 to 80 mph and the median speed is 5-8 mph lower. The Arkansas measurements are nearly 20 mph apart. On urban freeways the measurements are 11 mph apart.

I believe Arkansas DOT did not report the speed of free-flowing traffic (as required by the Manual On Uniform Traffic Control Devices), but rather an average including all types of traffic flow. Cycles of congestion and weather will increase apparent variance in speed and depress all percentiles, explaining Arkansas’ graphs. For example, if drivers go 80 on a clear day and 50 during a busy, rainy holiday weekend, the combined speed distribution will be very broad, from 50 to 80. Posting a 70 mph speed limit based on the aggregate data would create a very high violation rate during the times when speeding tickets are written. In this case the speed limit should be based on the 80 mph free flowing condition, not the 50 mph traffic jam.

The study also recommends posting 65 on rural four and five lane roads other than freeways, with increases not allowed. Such roads tend to be posted 65 or 70 except on the East Coast.

The standard speed limit on rural two lane highways would remain at 55, but increases to 60 would be allowed. This is based on data showing the speed limit should be 60 in hilly terrain and 65 in flat terrain. Such roads tend to be posted 60 or 65 except on the East Coast, but some states post 70 or 75.

If any readers in the South have laser guns, a trip to the nearest freeway could yield interesting data. While it’s possible a 75 mph speed limit is justified, I find the report unconvincing. I’d like to know what’s really going on out there.

The opinions expressed in this post belong to the author and do not necessarily represent those of the National Motorists Association or the NMA Foundation. This content is for informational purposes and is not intended as legal advice. No representations are made regarding the accuracy of this post or the included links.

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2 Responses to “Arkansas DOT accepts 75 mph request”

  1. Tom Beckett says:

    Some thoughts from a Siloam Springs(on US 412 at the OK line) resident:

    I find the average rural interstate speed of 52 MPH dubious. That would mean significant numbers of drivers running in the 40 MPH range, which would be immediately noticeable. We have our share of slowpokes out here(usually in the left lane), but not that many. I drive I 49 in NW Arkansas several times a week, I 40 from Alma to Little Rock perhaps a couple dozen times a year, with a few less frequent trips to Memphis. My observation is that traffic is moving somewhere in the 65 to 80 MPH range during good conditions. Most of those routes don’t have a lot in the way of congestion(to my ex New Yorker mind), though I 40 can be pretty busy, as it is a coast to coast highway.

    The physical characteristics are mostly flat east of Little Rock, with some minor topography(Crowley’s Ridge near Forrest City) between Memphis and Little Rock. West of Little Rock, it’s hilly til Clarksville, where it goes into the Ozark Plateau and the Boston Mountains, with a lot of hill climbing from there to about Mulberry. It ain’t Donner Pass, but it will slow down the heavy trucks. I 49 from Alma to Fayetteville is straight through the Boston Mountains, with a lot of steep grades, and a tunnel at MP 41. It reminds me of the Pennsylvania Turnpike in places. I’m not sure a 75 MPH speed limit would accomplish much on I 49-it’s 70 now-since the topography largely makes it a moot point.

    I 40 does suffer from congestion at times, especially east of Little Rock, which is a choke point and one of the busiest stretches of interstate in America. Everything going to and from Texas and California to the mid south or southeast, and a lot of traffic to the east coast runs this way, and truck traffic is heavy almost all the time. Most of the large fleets are governed somewhere in the 65-75 MPH range, with a few slower(JB Hunt and Prime seem to always be holding things up). That section of I 40 is four lane, so if a 68 MPH truck passes a 65 MPH truck, it holds everything up while the pass is going on. Add in the aforementioned slow pokes, motor homes, utility trailers, etc, and it makes for a slower trip than 70 MPH a lot of the time. That part of I 40 really needs to be six lanes, which would eliminate a lot of those problems.

    At present, interstates are posted 70, with urban sections in Little Rock, Fayetteville, and West Memphis posted 65, with a couple of sections in Little Rock and Fayetteville at 60. Four and five lane(a four lane, non divided highway with a left turn lane) are posted 60, with some 55; four lane divided non limited access highways are 65. Two lanes are 55 MPH statewide.

    By comparison, Oklahoma posts its interstates at 70-as far as I know, there is no move presently to increase that-and Turnpikes at 75. Four lane divided are 65 with some 70; two lanes are mostly 65, with some in hillier and more densely settled areas at 55. Texas posts interstates at 75, with some segments in more remote places at 80; all other roads, two or four lane, are posted 75 for the most part once you’re out of town. Missouri is 70 on interstates, 65 on some four lanes, and 60 on most two lanes, with a good number of them at 55.

    My assessment as someone who drives on the roads here is that the interstates could be safely posted at 75, and I’m thinking that will happen once this gets through ARDOT. The non interstate multi lane roads could go to 65, and some of them 70, with no problem, and many of the two lanes could go to 60 safely. If I had to bet, my money is on this getting implemented, unless it becomes a political issue, which doesn’t seem likely, as it has not been controversial thus far. Traffic is already moving at those speeds most of the time as it is.

  2. toly arutunoff says:

    the speed limit in Arkansas on interstates was 75 until the ’55’ came into effect; 75 was very lightly enforced.