The City of Greenwood, Indiana is proposing a modified Michigan Left with dual roundabouts for the intersection of Smith Valley Road and State Rd 135:
http://www.indystar.com/story/news/local/johnson-county/2014/10/10/michigan-left-greenwood-johnson-county/17045019/
Seems like a good idea, but I'd make the right turns onto Highway 135 slip lanes, so fewer cars have to come to a stop, which would help keep the roundabout flowing.
This makes sense given its proximity to the other intersections and that they can't install the wide medians normally seen with a Michigan left. It will probably work just fine. But man, I'm not used to an official solution looking like this. If not for the article, I'd assume the Michigan left functionality of the roundabouts was accidental. It's just weird. Good, but weird.
Interesting that the north-south road is keeping the direct left turn lanes. That means there's still a signal phase that could have been eliminated, but at least the roundabouts are less likely to be overloaded this way.
"The plan, which Mayor Mark Myers calls a "dual roundabout," won preliminary federal approval. "When you use a dual roundabout, you're not stopping traffic," Myers said. "You don't have to worry about the cross traffic and stop light maintenance.""
I'm confused - isn't there still going to be a traffic light, so traffic can go across the intersection?
It seems like the mayor is reaching to find something good to say here. Is he having an issue with the other numerous lights in his town?
Quote from: jeffandnicole on July 28, 2015, 07:35:20 PM
"The plan, which Mayor Mark Myers calls a "dual roundabout," won preliminary federal approval. "When you use a dual roundabout, you're not stopping traffic," Myers said. "You don't have to worry about the cross traffic and stop light maintenance.""
I'm confused - isn't there still going to be a traffic light, so traffic can go across the intersection?
It seems like the mayor is reaching to find something good to say here. Is he having an issue with the other numerous lights in his town?
Mayor Mark Myers comments are likely based on a Michigan left that was recently completed at 96th & Allisonville Rd in Fishers, Indiana. The Michigan left in Fishers has 5 traffic signals (1 main signal plus 4 crossover signals). OTOH, the proposed Michigan left in Greenwood will only have 1 traffic signal at the main intersection (with crossover traffic serviced by the dual roundabouts).
Compare the number of traffic signals that stop both directions of travel along a 5-mile stretch of Big Beaver Rd in Troy, Michigan (MUT corridor) to a 5-mile stretch of State Route 135 in Greenwood, Indiana (standard corridor).
Big Beaver Road (Troy, Michigan):
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FMichigan%2520Lefts%2FBB5_zpskfwgucg0.png&hash=c019368676f6d3fc132c33d7d527daf2a6c00326)
State Route 135 (Greenwood, Indiana):
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FMichigan%2520Lefts%2FState135_zps4cduwuhv.png&hash=fb98986ae58c211fc1f7180a4a4c831f8e6922cd)
The wide median of Big Beaver is the main reason why it has fewer traffic signals. With wide medians, drivers can turn right to go left. Oftentimes, this right-to-turn-left approach avoids the need for a traffic signal entirely (and if a signal is warranted, it only stops one direction of travel). Compare that to a standard corridor... traffic signals stops both directions of travel for seemingly every office complex, school, church, strip-mall, and sub-street. The number of signals adds up fast and kills signal progression.
Here's a good video detailing the Median U-Turn (Michigan left) corridors that are common in metro Detroit. The design would be more effective if it was looked at as a corridor improvement as opposed to a spot improvement. How effective will a Michigan left be at Smith Valley Road and State Rd 135? Sure, drivers along State Rd 135 might make it through Smith Valley Road a little easier, but they will likely just get stopped at a signal 2,000 feet down the road (while a direct left-turning vehicle exits a strip mall).
https://www.youtube.com/watch?v=rvazA22vhN0
Quote from: tradephoric on July 29, 2015, 02:21:58 PM
Compare the number of traffic signals that stop both directions of travel along a 5-mile stretch of Big Beaver Rd in Troy, Michigan (MUT corridor) to a 5-mile stretch of State Route 135 in Greenwood, Indiana (standard corridor).
Big Beaver Road (Troy, Michigan)://snip//
You forgot the signals at the ends of the exit ramps. True, they don't line up with each other on the EB and WB sides and sometimes are in blinking mode. But both sides do have lights, and both directions do need to stop from time to time.
^There are traffic signals along Big Beaver at the I-75 on/off ramps. The key point is those signals only stop ONE direction of travel. It doesn't guarantee that you will never get stopped at these lights but it increases your chances of making it through.
Well, you're only driving in one direction at the mile-spaced intersections as well. I don't see how that makes it more or less likely that you'll need to stop at the freeway. It depends on the lights' timing and duration.
Of course the lights at the MI-left turnarounds are timed with the main intersections so thru traffic won't usually have to stop twice.
Quote from: GaryV on July 29, 2015, 07:39:22 PM
Well, you're only driving in one direction at the mile-spaced intersections as well. I don't see how that makes it more or less likely that you'll need to stop at the freeway. It depends on the lights' timing and duration.
Here's a time-distance diagram for the major signals along Big Beaver Road. The hard part is providing good dual progression at signals that stop both directions of travel. From there, the signals that only stop one direction of travel become a breeze to coordinate. They just tie into the main signals.
(https://www.aaroads.com/forum/proxy.php?request=http%3A%2F%2Fi478.photobucket.com%2Falbums%2Frr144%2Ftradephoric%2FTransportation%2520Pictures%2FRandom%2FABigBTD_zps07stxecr.png&hash=cbf3a4fad9e9ddbe1e7fea3977bd3edd1fe915c1)
https://www.youtube.com/watch?v=o2BOYF0JQFE