The intersections limit points where vehicles could collide by forcing drivers on side roads to turn right, go a short distance down the road, make a U-turn through the median, then loop back to the intersection to continue their trip...Minnesota's first J-Turn intersection was built in 2009, and now more than 60 exist statewide (2022) with more planned. They have been credited with significantly reducing right-angle crashes resulting in serious injuries and deaths...Despite J-Turns' safety benefits — data showed they cut fatal and serious injury crashes at intersections by 69% — it's been tough to convince the public, said MnDOT traffic engineer Derek Leuer."They have never seen one," he said.And when they do encounter the intersections, drivers are not fond of them.
The Wikipedia entry provides some discussion.
Addendum: A reader offered this screencap from Google Maps of a J-turn setup with no option for straight-across crossing of the divided highway. Basically, this creates a elongated roundabout -
- but maintains higher speeds on Highway 1, where a true suburban roundabout would potentially bring main highway traffic to a stop at busy hours. Interesting.
J turns are more safe than regular crossings, but still fundamentally unsafe in the sense that cars (and especially trucks) are still crossing several fast-moving lanes.
ReplyDeleteThe ideal solution is an overpass.
Or less car traffic.
After living in Michigan, the land of J-turns for 20 years, I would say the main thing they do is cause locals to take parallel roads with conventional crossings in order to avoid them.
ReplyDeleteAfter living in Michigan my entire life and dealing with J turns since they were first brought into use. I would say, they work great, not a problem and in fact they're faster than screwing around with the left turn light.
ReplyDeleteJust like roundabouts and the new double diamond intersections they're just something new that some people have trouble accepting because "that ain't the way my daddy did it"
Has anyone studied whether there has been an increase in u-turns through medians where they are NOT allowed? Most such spaces I've seen are not meant to be so used, except by official vehicles (and speed traps...).
ReplyDeleteSandra
How about round-a-bouts? Or traffic circles? Is Michigan a non-circular anti-roundabout state???
ReplyDeleteThere have been roundabouts in Michigan since at least the early seventies when I Learned to Drive, although not in great quantity. Recently they've started appearing everywhere.
DeleteThe J turn is very useful in places where there isn't room to put in a round about.
I believe it's also cheaper and faster to put in.
We have something like that here in RI, on Route 1 in South County. Those allow a car to cross Route 1 (a two lane 'highway') without having an intersection. To do that, they enter from the side road, have to make a right onto Route 1 (heading in the direction opposite to where they want to go), and then quickly move to the left lane and make a U-turn to get on Route 1 heading in the direction they want to go, and then exit onto the road they want to be on. Unfortunately, many of those are poorly laid out. You very often see cars way over in the right lane, waiting for an opening so they can dash across two lanes to get to the U-turn lane that is a third lane way on the left. Similarly, you see cars sitting in at the end of the U-turn, way over on the median, waiting for an opening so they can dash across three lanes to get off Route 1, or to get on to Route 1 (they are entering the two lane 'highway' via a left side entrance). Meanwhile, the speed limit on Route 1 is 50, but traffic usually goes at 60 and plus. You end up with slow cars dashing across three lanes of fast moving traffic.
ReplyDeleteA google maps sat view of one of those Route 1 U-turners https://maps.app.goo.gl/v8KYfMacydnfpa8c9
ReplyDeleteThank you for sending that; I've added it to the body of the post. I've not seen a setup like that before.
DeleteThere have been such turns on RT 301 on the Eastern Shore of MD for decades.
ReplyDeletewhere a true suburban roundabout would potentially bring main highway traffic to a stop at busy hours
ReplyDeleteSorry, gotta vent a pet peeve here.
Roundabouts NEVER stop traffic. Traffic is always flowing*.
STOP lights STOP traffic, just like TRAFFIC lights cause TRAFFIC.
* yeah yeah, except when there is no one around, or when there's a crash blocking blah blah.
I can confirm from personal experience that roundabouts DO STOP TRAFFIC. You are correct that traffic is "always moving" IN the roundabout - but not necessarily in the access lanes. I pass through a suburban roundabout every week on my grocery shopping trip to Target. Our state law requires yielding to vehicles already in the roundabout, and that yield will include stopping when there is no room to merge safely. Usually one can adjust one's approach speed to fit in before or after vehicles already circling, but if there is a train of vehicles in the (one-lane) circle, then you have to stop. BTW, I love roundabouts.
DeleteYou are correct that traffic is "always moving" IN the roundabout
DeleteGood. And let's also acknowledge that this is NOT the case with traffic lights, where there is always a moment of completely stopped traffic as the lights change, but also many moments of stopped traffic as the green light lane has emptied out - this could be prevented if DOTs were to use technology to prevent that, but they're too lazy to do so.
That technology exists, as I've noticed in my recent travels home to the Netherlands. You can do amazing things with smart traffic lights, including speed limit enforcement.
but not necessarily in the access lanes
This is true for every busy intersection. But, since traffic is always moving IN the roundabout, as opposed to the traffic lights, the lines are shorter than they would be with a traffic light. Which means you're still getting through faster than you would with a traffic light.
Our state law requires yielding to vehicles already in the roundabout
This is logical, right? If you didn't do that, the roundabout would have to accept more traffic coming on than can get off, which is physically impossible. So this is a good rule.
Usually one can adjust one's approach speed to fit in before or after vehicles already circling
As great built-in safety feature of roundabouts is that they slow traffic down reducing the number of full-on crashes. This is good.
but if there is a train of vehicles in the (one-lane) circle, then you have to stop
The only time traffic circles do not work well, if is there is one feeder road that has a constant flow of traffic because that blocks traffic from the next feeder road on the roundabout. It is very possible that this is the case at a shopping location, because those are often terribly designed.
Considering the refusal of legislatures to force better mall parking lot designs*, something the local DOT could do is increase capacity of the roundabout by making it a two lane or even a turbo roundabout.
* If you would suggest such a thing, people would rumble about free markets and letting store owners do what they think is best, but I don't understand why it somehow is always the local DOTs problem then to clean up the mess of the terrible traffic streams just outside the mall created by the horrendous design of mall parking lots. These terrible mall parking lots are a uniquely American thing. That sadly is being exported to the rest of the world.
Maybe you can add this https://xkcd.com/2932/ Driving PSA - about someone waving you into traffic and there are cars behind them
ReplyDelete