Prediction: I-270 Bears the Brunt of the Highway 40 Construction (Updated)

With the January 2nd shutdown of Highway 40/I-64 just two months away, the conventional wisdom is that the major traffic headaches will be seen on roads that parallel the closed portion of the highway. Clayton, Ladue, Manchester, and Olive will surely see substantial increases in traffic. As will I-44 and I-70, though those interstates will be able to absorb the traffic due to the added lanes on those roads (see recent article on the safety of that move). Yet, I don’t think it’s any of these roads that will bear the worst part of the traffic congestion after the shutdown. Rather, it will be I-270 that gets hit with the crawling traffic on a day-to-day basis.

First, we need to realize that I-270 is already running near capacity during most rush hours. Next, imagine the fire hose of traffic that’s eastbound on Highway 40 any morning. It will be forced to divert north or south on I-270, as shown on the map below. Chances are that most of drivers will choose the southbound route, since I-44 exits are closer to their Highway 40 counterparts than I-70. The result? Delays and jams on I-270, particularly between Highway 40 and I-44.


[Zoom and pan the map as needed; Click on markers/routes for more information; full map]

It won’t be just I-270 that gets the diverted traffic. Many of the north-south arteries in West County, such as 141 and Lindbergh, will struggle under the load of drivers finding new routes to their destinations.

It seems that some of the county’s traffic experts are worried as well. Garry Earls, director of the County’s Department of Highways and Traffic, had the following to say at a recent meeting of the I-64 Connection Subcommittee:

Garry Earls strongly recommended that state transportation officials do everything within their power to encourage east-bound I-64 motorists to take north-bound I-270 – once the interstate closures begin early next year. Earls is concerned that too many I-64/40 drivers will try to circumvent the closure by taking I-270 south to I-44, and thence to Elm Avenue. “The overwhelming majority of east-bound I-64 traffic is headed for Clayton, and I-44 won’t be able to handle them,” Earls predicted. “We have to figure out how to get those cars to the north – not the south, because we don’t have a place to put them. We have a place to park them, and that place is Webster Groves.

Earls continued to say that these motorists – rather than using I-44 to access the central corridor – must be given every incentive to take I-270 north from I-64 to reach Olive and Page.

MoDOT’s Ron Morris responded that the state can’t force motorists to take I-270 north from I-64, but that he would consult with other MoDOT traffic engineers about the possibility of providing an additional exit lane onto northbound I-270 for I-64 drivers to
use.

[source]

What are your thoughts? Where will the worst jams be in January of 2008? Leave a comment by clicking on the link below.

UPDATE 11/4/07:

It seems Fox 2 liked this posting. Friday they had an interview with Gerry Earls and showed a map very similar to the one above (down to the color of the routes). Glad someone’s reading!


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.


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