By Michael Brown, PE, AICP
This article features a family of innovative intersection designs collectively called “Thru-Turns” – which includes Thru-Turns, Bowties, and Michigan-Lefts. Virtually none in existence are great place-makers, but they have untapped potential. I wish I had great renderings to reveal their potential – not my talent. If some of you who are designers catch a glimpse of that potential from this article, then contact me and let’s work on better renderings, and I’ll feature your work. Maybe we can get a showcase built somewhere and finally deliver a great new concept to the field.
Can the tortoise win the race? Watch this video first, or read the introduction article titled Place-Making Innovative Intersections.
Please comment or view comments about Thru-Turn Intersections at the end, and if you like it please share with anyone who might care. You can also contact me privately to learn more.
Have you ever tried to turn left from a parking lot onto a busy arterial, and found it so impossible to get a gap in both directions that you instead went right, then made a U-turn? A Thru-Turn simply formalizes this action.
In these diagrams, some lefts are completed as “Right-U-Thru.” Others are “Thru-U-Right.” Bowties, Loons, Median-U’s, Superstreets, and even roundabouts can generally be included as part of the Thru-Turn family.
Rerouting lefts along 10-15 mph roundabouts in a retail center
Without lefts, the main intersection has fewer conflicts, making it safer for pedestrians. With no need for left turn pockets, former pockets can be pedestrian refuge, transit, and other uses.
This concept is also known as a “Michigan Left.” Decades ago, Michigan required a number of state highways to have very wide medians so that these U-Turns could occur. Other states lack wide medians, but often do have deep setbacks and under-utilized parking where ellipses, bulb-outs, or roundabouts could be carved out without excessive impacts.
Ellipses & roundabouts create interior space which can be used as a transit station or gateway landscaping helping define a “Place.” They also help calm traffic before it enters a pedestrian-oriented space.
Imagine a 7-lane arterial crossing another 7-lane arterial, with double-left turn pockets on each approach. Pedestrian Purgatory! This Bowtie design can replace that, improving walkability and livability. The ellipses redirect left turns as “right-U-thru” or “thru-U-right,” and also serve to calm traffic. Space inside the ellipse can be used for landscaping, a transit station, and to define the entry to a key “Place” in the community. Former left-turn pockets become pedestrian refuge as shown.
Yes, these will still be major highways with a lot of traffic, but speed limits in this area can now be reduced without reducing average traffic speeds. It is functionally safer, faster, prettier, and less intimidating for pedestrians than it was before, and reinvestment in mixed-use development can start to occur.
This was Utah’s first Thru-Turn, a 3-leg design that opened in 2011. It eliminated congestion (2-minute average to 26-seconds). Unfortunately it’s ugly – done “on the cheap” with a focus on cars. No pedestrian refuge, landscaped ellipses, lower speed limits, and other place-making features. Community reception was mixed. They liked reduced congestion, but hated confusing paths and the ugly, auto-oriented result. Lesson: If your first thru-turn doesn’t invest in place-making to help counter public distaste for out-of-direction travel, you may not get to build another one!
|Advantages of Thru-Turns & Bowties||Disadvantages|
|Impressive vehicle-capacity gains||Initial confusion for drivers|
|Shorter signal cycles||Out of direction travel for lefts|
|Safer for both autos and pedestrians||Space required for bulb-outs / ellipses|
|Enhances and motivates TOD||Educational effort to win over skeptics|
|Often very low cost||Still high volume – doesn’t make cars go away|
|Politically easier to obtain transit lanes|
|Traffic Calming / Gateway Feel|
|Planted medians, access control, circulation.|
|Compatible with traditional signals|
|Former lefts reclaimed for center-running transit, pedestrian refuge, etc.|
ThruTurnIntersections.org has a collection of existing locations (not comprehensive), along with videos, articles, and other links.
Please comment on or ask questions about Thru-Turns and Bowties! I like to think I know everything, but I’m just an engineer trying to help broker deals between New Urbanists and Sad Reality, and we need to hear more from both Urbanists and Reality if we’re to discover how these ideas can really help.