Are Narrow Lanes on I-44 and I-70 Safe?

In preparation for the Highway 40/I-64 shutdown this January, MO-DOT is in the process of restriping I-44 and I-70, a process which will add an additional lane for the anticipated alternate route traffic from the shutdown. The Post-Dispatch covered the topic in an article today. What caught my eye, though, was this section:

Officials say there’s no evidence that the narrower lanes will increase the number of traffic crashes.

“We haven’t seen any difference in the accident statistics,” said Linda Wilson, spokeswoman for the Transportation Department. “We aren’t aware of any research that shows statistically more accidents.”

Really? I did a quick Google search for “narrow lane accident rate”. The second item on the list was a study from the U.S Department Transportation on how adding a lane on an urban highway affects accident rates. It’s key finding:


The analysis results indicate that narrow-lane or shoulder-use-lane projects on urban freeways increase accident frequencies for four- to five-lane conversion projects.


(from: “Safety Effects of Using Narrow Lanes and Shoulder-Use Lanes to Increase the Capacity of Urban Freeways“)

Now, as with any study, there are a lot of details. I sorted through the discussion on Empirical Bayes Analysis and statistically significant results. The above results are statistically significant. The only caveat is that many projects in the study added a High Occupancy Vehicle (HOV) lane as part of the project, which could contribute to the accident rate, though that was not analyzed specifically.

Furthermore, the study postulates that “downstream” traffic may also have increased traffic rates. An example of this in St. Louis would be eastbound I-44 which will be restriped to have 5 lanes. Near the I-55 junction, though, those 5 lanes get reduced to just 2. That junction may prove to be more accident-prone according to the study.

So, a 10 minute Google search by a non-traffic engineer turns up a study showing statistically more accidents when lanes are narrowed on urban highways. Yet MoDOT couldn’t find such evidence? Did they really look, or was it more convenient to state that their actions are safe? I don’t expect a MoDOT spokesperson to be thoroughly read on all the latest traffic engineering studies. But I do expect that MoDOT employs traffic engineers who do read these studies and who consider those studies when making traffic changes.

This entry was posted on Tuesday, October 16th, 2007 at 8:37 pm and is filed under I-44, I-70, Safety. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

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