Update: Lane Shift Standards

Lane Shift guidelines In a previous post, I documented drivers’ behavior at the lane shift at Highway 40 and Tamm Avenue, which many of you agreed was dangerous. In looking for ways to make this area safer, I noted that the lane shift at I-270 and Dougherty Ferry used solid white lines for lane markers instead of dashed lines like at Tamm. It was much easier to stay in the lane with these bright solid lines. These two construction projects are handled by different contractors, so I asked MoDOT what standards they specify. I received a quick and professional response from MoDOT:

At the core of the issue, Federal Highway’s Manual on Uniform Traffic Control Devices dictates the guidelines we use for lane shifts. If you have a dramatic lane shift, or one that requires a quick traffic movement, the manual dictates using solid lanes. If the lane shift is a little more gradual, it is acceptable to use the dashed lines. Often times, the determination on the traffic impact of a lane shift is made by the person designing that particular traffic movement. So, though MoDOT doesn’t provide guidelines per se (since we use Federal mandated guidelines), we will adhere to, and ensure contractors adhere to, those guidelines. As with every guideline, though, there is some area for interpretation.

If you’d like to read the guidelines on lane shifts for yourself, here are links to the notes and the details . The guidelines seem to lean toward using solid lines as lane markers, but does leave it open to some interpretation.

At MoDOT’s recommendation, I will submit a comment form to the Highway 40 project team, asking them to look at the video I shot to see if solid white lines might be an improvement in this area. I’ll keep you up-to-date on their response.

Update 6/22:

I received the following response from the I-64 Community Relations team. They are not considering use of solid lane lines at Tamm, for reasons they describe below. So the best advice for now is to stay vigilant when driving through these lane shifts.

EB I-64 at Tamm, the traffic shift is fairly minor, and the use of solid lines is not recommended. WB I-64 at Tamm the lane shift is more noticeable on the inside lanes and very minor on the outside lane. This is caused by the lanes narrowing from 12′ to 11′ in the work zone, with the outside lane experiencing the smallest shift.

At this time, the use of solid lane lines between each lane is not being considered. One of the main reasons for this is that the transition points for the stripes use curves opposed to hard angle points and taper-style lane shifts. The taper lane shift is shown on the MUTCD excerpt on your blog; meaning, there are hard angle points where the stripes force traffic to turn abruptly to remain in their proper lane. The Tamm workzone lane lines use curves allowing for smooth transitions around the work zone. Plus, the striped curves are designed to handle 55 mph interstate traffic, so no speed reduction signs are necessary. By designing the traffic shift to current speed limit, the need for solid lane lines between lanes is also reduced.

This entry was posted on Wednesday, June 20th, 2007 at 11:26 am and is filed under General, Tamm. 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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