I was waiting for the number 6 bus at Hennepin Ave and S 1st St, near where I live, and I was watching the vehicle traffic. I noticed that the semaphore intersection was not very efficient at handling left turn vehicles. There was a part of the cycle when left turns in both directions on Hennepin Ave would go, and I saw a trickle of 2-5 cars make their turns as traffic backed up in all directions. There also was the flashing yellow arrow left turn, which worked like a regular green light, having left turners yield to oncoming traffic. The time was just before 5:00 PM, so there was heavy traffic in both directions.
Taking this in, I wondered if it would be possible to build a roundabout at the intersection. After my evening meeting, I opened Google Earth and saw the radius of a circle that one could draw. This happened to be about 95 feet.
According to the Federal Highway Administration (FHWA), a roundabout of 95 feet would have vehicle traffic travel at about 20 mph (page 55 of PDF). This is not the speed some cars go right now, but it seems to me like a reasonable speed to make the space safer and reduce accidents.
With these facts in mind, I started to design in Adobe Illustrator a simple roundabout with a couple of unique features. I was influenced by a 2017 Vox feature on “shared space” traffic intersections in Britain. I decided to draw up a hybrid of a shared space — where there are no traffic lights and cars, bikes, and pedestrians share the road — and a standard FHWA roundabout where pedestrians cross a single right-of-way (street) like a traditional intersection.
The first thing to note about this design is that it reduces lanes. Left-turn and right-turn lanes are eliminated in return for more space for pedestrians.
The second note is that I designed the roundabout with 10-foot lanes. This is likely narrower than the current lanes, but would reduce vehicle speeds approaching the roundabout. However, there does appear to be space for a 20-foot, or two-lane, roundabout, and that is what is drawn here.
Benefits of a roundabout design
As a daily pedestrian, I appreciate traffic design that reduces the chance I may get run over by a postal semi when I run to grab a cup of coffee. Right now, there are many left turns from S 1st St that can be problematic for pedestrians crossing Hennepin Ave. The left-turn drivers are focused on avoiding a head-on collision and yielding to pedestrians is a secondary priority.
This design eliminates those issues. First, pedestrians only cross up to two lanes of vehicle right-of-way. Second, the traffic has a stop signal, and remaining traffic in the circle is coming from only one direction. In the current setup, pedestrians contend with right turns from drivers facing the other way and aforementioned left turns.
The vehicle signals would be either red arrow (stop, no right turn) or flashing yellow arrow (yield to other traffic).
Another feature of this design are bus lanes on both Hennepin Ave and 1st St. Buses park on 1st St as it is, and creating more space for buses will improve transit on-time performance and reduce bunching. Before writing this, I saw three 2C buses bumper-to-bumper on 4th St SE.
One question that a planner would need to address is how much time should be allocated to the pedestrian portion of the signal. The FHWA recommends designing for a walking speed of 3.5 feet per second. The question is whether to time for crossing one street or going across the diameter. Going across the diameter of the roundabout design would be about 54 seconds. If there was public art or other barriers in the middle, the time could be up to 85 seconds. Of course, there could be a short time of say 30 seconds and pedestrians would have to wait a cycle before completing their trip across both Hennepin Ave and 1st St.
I am not a public works planner or engineer, but I am a pedestrian, a transit rider, and a driver on occasion. It saves lives and improves livability to have streets that don’t work like highways with switches. Putting a roundabout on Hennepin may be radical, but so were a lot of things we take for granted now.
Do you cross streets or speed through them? What do you value as a pedestrian? What public art would you put in the middle of Hennepin? Share your stories and insights in the comments.
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