Roundabout Lessons on Scaling Lean Solutions

Traffic roundabouts are one of my favorite flow management devices. There is a physical WIP limit. They’re visual. Look to the left for oncoming traffic, if there is a gap, this is the “pull signal.” No oncoming car in the circle means there is capacity in the system to start the next increment of work, or travel. They run on simple rules.

Roundabouts promote a continuous flow of traffic, replacing the mindless act of stopping when the light is red, even if there is no cross traffic. Roundabouts’ function is not disturbed by power outages that affect traffic lights. In addition, their long term cost is lower due to lack of maintenance of traffic lights. Roundabouts are faster, cheaper, better, and safer.

How Roundabouts Reduce Collisions

Roundabouts help reduce the incidence and severity of traffic collisions. This is because we reduce our speed and yield to other drivers when driving through them, to about 15 to 20 miles per hour. There’s a huge difference in the damage at those speeds versus a car speeding through at 60 mph.

By design, the traffic in a roundabout is one-way only. The road curves around, allowing cars to enter or exit in one direction. T-bone and head-on collisions are very rare because it would take a lot of effort, or ridiculous speeds to wedge a vehicle in against the direction of traffic.

Drivers yield to oncoming traffic, but proceed if there is none. There’s no traffic light to beat, so there is no chance for the bad behavior of accelerating through a yellow light and colliding with cross traffic. The design for continuous flow eliminates the incentive to go dangerously fast.

Clarity & Rule-Following vs. Ambiguity & Judgment

We have one roundabout in our town at an intersection near a high school, parochial school and church, library, apartment complex, and supermarket. It works remarkably well. In the past year, the city has built a second one about two blocks south on a corner that has a house, a wooded lot, an architect’s office, and a car mechanic. It’s a puzzling choice. This new roundabout has been receiving mixed reviews from the citizens.

The roundabout in this intersection looks different. There is no signage other than painted white marks on the road. The central circle is flat and barely distinguishable from the road on approach. There is no landscaping. The turns are sharper, as the roundabout was built into a smaller space. Some drivers were confused. When it was first opened to traffic, a delivery van drove over the middle. Concerned citizens took to neighborhood message boards and sent emails to city hall.

It turns out the new traffic control device in our town is something known as a mini roundabout. It’s identical in principle to a larger roundabout, only due to its dimensions, it requires that drivers pay more attention. While we’ve grown used to the rules of the standard roundabout, the physical features of the mini roundabout left these ambiguous. It required human judgment. Should I stop? Proceed? Avoid driving over the shallow speed bump, or..?

Lessons on Scaling Lean Solutions

This experience raises interesting questions about scaling lean solutions across an organization. Lean thinking tells us that ideally, we take a good idea and try to copy it wherever we can. But to what degree can we modify a proven solution to suit local conditions before it breaks down? How far up can we scale this solution? How far down?

Obviously if a roundabout’s diameter is too small, vehicles on that road may not be able to make safe turns. It feels like we are near this point with the mini roundabout in my town. On the other hand, there’s the grand 12-lane roundabout at the Arc de Triomphe in Paris. This demonstrates that we can scale up roundabouts quite a bit. It’s hard to quantify the scale at which good practices, systems, or solutions begin to break down.

However, we can draw a few general lessons from this roundabout example. First, we should be careful not to assume that a solution that works in one context will work as well in a different or modified one. Second, we need to understand the ancillary characteristics that help reinforce the desired behavior pattern, such as visual controls, advance communication about the change or solution, and ongoing education. Third, a poka-yoke, context-specific, mistake-proofing mechanism should be employed whenever possible. This alone would have prevented this mini roundabout mini drama. I have half a mind to do the city a favor with some midnight gardening, breaking asphalt and planting a tree in our mini roundabout.

4 Comments

  1. Jesse Stevenson

    May 24, 2021 - 8:24 am
    Reply

    I loved reading this. I hadn’t thought about the round a-bouts in this context. I’m anxious to share with my class

    • Jon Miller

      May 24, 2021 - 1:17 pm
      Reply

      Glad you liked it Jesse.

  2. Richard Shelmerdine

    May 24, 2021 - 11:03 pm
    Reply

    A fascinating read, thank you.

    I would like to challenge your analysis of a mini roundabout a little, if I may.

    Driving over a mini roundabout is available for longer vehicles in such a location where existing infrastructure does not allow for a ‘normal’ roundabout + truck apron.
    The first image you chose for this article shows such a truck apron; outside the grass but inside the area where shorter vehicles drive.

    Whilst acknowledging that some of the benefits of the larger roundabout do not scale down, assuming that your described benefits of a roundabout continue to hold true – and to this list I would add disinclination for a forced stop at a four-way stop – what type of junction would you prefer to see?

    At the very least, please speak to the delivery drivers at the supermarket you write about before planting your tree :o)

  3. Jonathan Wiederecht

    June 8, 2021 - 12:46 pm
    Reply

    Jon,

    Can’t wait to see what kind of flowers and trees you plant!

    Jon

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