5 ms·

I used to live in Michigan, where we have a thing we call the "Michigan left". To turn right at an intersection, you continue straight through the intersection,

by ahepp 5y ago

I used to live in Michigan, where we have a thing we call the "Michigan left". To turn right at an intersection, you continue straight through the intersection, then take a left turn at gap in the median to return to the intersection from the other side of the boulevard and proceed to make a right turn. I'd be interested in what the trade-offs are. I imagine space usage is a big one.

tyingq 5y ago
If that's hard to visualize: https://bloximages.chicago2.vip.townnews.com/tctimes.com/content/tncms/assets/v3/editorial/f/f3/ff3e874c-27db-11e4-b3b5-0019bb2963f4/53f3adcf0d9a9.image.png https://bloximages.chicago2.vip.townnews.com/tctimes.com/con...
- red_hare 5y ago
  That's very helpful. Thanks!
jldugger 5y ago
> To turn right at an intersection Pretty sure you mean 'to turn left'
cornstalks 5y ago
> To turn right at an intersection... You mean to turn left, correct? I've seen this technique used by people as an optimization. Some lights have very long wait times for left turns, so people will do what you describe rather than waiting in the left turn lane.
deanCommie 5y ago
Looking at the diagram [0], I'm dubious if this is a good "authoritative" solution. The problem with left turns is collision with oncoming traffic moving straight through. Especially at yellow lights where the turning vehicle is trying to make it out of the intersection before the light turns red and they feel like they are blocking 90-degree traffic [1], and end up colliding with oncoming vehicles running the yellow. This design seems to shift that problem 100 meters down the road, but the challenge of crossing oncoming traffic remains (I guess without the pressure of trying to get out of a turning Yellow Light situation). So it's definitely an improvement, but isn't there a simpler one called "Dedicated Left Turn Signals"? If both directions had an "advance left" light where both could turn safely, and there was a dedicated light for turning (i.e. no entering the intersection to turn except in a dedicated Left turn sign), this solves the problem, no? Dedicated Turn lanes and signals need space, so they're not always possible in dense urban environments, but the Michigan setup doesn't suffer from a lack of space. So i feel like the Michigan solution is useless for San Francisco, and also not as good as the alternative for Michigan [0] https://en.wikipedia.org/wiki/Michigan_left#/media/File:Michigan_Left.svg https://en.wikipedia.org/wiki/Michigan_left#/media/File:Mich... [1] Which, incidentally, FEELS unsafe, and inexperienced drivers panic trying to get out as soon as possible, but isn't actually - these vehicles are starting from 0 and accelerating - they are unlikely to accelerate INTO you. In rushing to get out before the light turns red, they are more likely to collide with an oncoming vehicle trying to run the yellow.
- ahepp 5y ago
  The major concern in the OP seems to be left turns hitting pedestrians. Eliminating the left turn over the crosswalk removes this problem. I would argue left turns to cross over the median aren't crossing oncoming traffic, they're merging into traffic going the same direction. Dedicated left turn light phases solve the problem too, but there's a cost to intersection throughput since there's an additional light phase (during which only left-turners on one axis can move). There are certainly a lot of trade offs to be made here with regards to space, cost, and safety.
Sparkyte 5y ago
Probably one of the safest ways to turn left as you have no bi-directional flows to compete against. When in a city and it is a grid I would just do the UPS right turn to make a left. One extra street down, right, right and straight.
- exhilaration 5y ago
  I feel like (in Manhattan, pre-covid) that would add at least 5 minutes to your trip. More doing rush hour.
  - Sparkyte 5y ago
    Well yeah... I wouldn't drive Manhattan funny enough.
dahfizz 5y ago
This sounds like a weird way to implement a jughandle turn. https://en.wikipedia.org/wiki/Jughandle https://en.wikipedia.org/wiki/Jughandle
- caspper69 5y ago
  It is sort of a jughandle, but the diagrams on wiki don't really do it justice. These exist on major thoroughfares where the destination road is divided. So you make a right and go to the far left lane, then go into a u-turn in the median where you can make a left turn in the desired direction without worrying about crossing oncoming traffic. Here's a link, and if you look at Telegraph Rd. just north of Maple (a few hundred yards from where Jimmy Hoffa was last seen alive), you can clearly see the traffic flow: https://www.google.com/maps/place/Telegraph+Rd+%26+W+Maple+Rd,+Bloomfield+Twp,+MI+48301/@42.5452613,-83.2858446,437m/data=!3m1!1e3!4m5!3m4!1s0x8824b850d128065f:0x735947c9c619db68!8m2!3d42.5448116!4d-83.2848117 https://www.google.com/maps/place/Telegraph+Rd+%26+W+Maple+R...
selimthegrim 5y ago
Also very common in New Orleans.

by ahepp 5y ago

tyingq 5y ago

If that's hard to visualize: https://bloximages.chicago2.vip.townnews.com/tctimes.com/content/tncms/assets/v3/editorial/f/f3/ff3e874c-27db-11e4-b3b5-0019bb2963f4/53f3adcf0d9a9.image.png https://bloximages.chicago2.vip.townnews.com/tctimes.com/con...

red_hare 5y ago
That's very helpful. Thanks!

jldugger 5y ago

> To turn right at an intersection Pretty sure you mean 'to turn left'

cornstalks 5y ago

> To turn right at an intersection... You mean to turn left, correct? I've seen this technique used by people as an optimization. Some lights have very long wait times for left turns, so people will do what you describe rather than waiting in the left turn lane.

deanCommie 5y ago

Looking at the diagram [0], I'm dubious if this is a good "authoritative" solution. The problem with left turns is collision with oncoming traffic moving straight through. Especially at yellow lights where the turning vehicle is trying to make it out of the intersection before the light turns red and they feel like they are blocking 90-degree traffic [1], and end up colliding with oncoming vehicles running the yellow. This design seems to shift that problem 100 meters down the road, but the challenge of crossing oncoming traffic remains (I guess without the pressure of trying to get out of a turning Yellow Light situation). So it's definitely an improvement, but isn't there a simpler one called "Dedicated Left Turn Signals"? If both directions had an "advance left" light where both could turn safely, and there was a dedicated light for turning (i.e. no entering the intersection to turn except in a dedicated Left turn sign), this solves the problem, no? Dedicated Turn lanes and signals need space, so they're not always possible in dense urban environments, but the Michigan setup doesn't suffer from a lack of space. So i feel like the Michigan solution is useless for San Francisco, and also not as good as the alternative for Michigan [0] https://en.wikipedia.org/wiki/Michigan_left#/media/File:Michigan_Left.svg https://en.wikipedia.org/wiki/Michigan_left#/media/File:Mich... [1] Which, incidentally, FEELS unsafe, and inexperienced drivers panic trying to get out as soon as possible, but isn't actually - these vehicles are starting from 0 and accelerating - they are unlikely to accelerate INTO you. In rushing to get out before the light turns red, they are more likely to collide with an oncoming vehicle trying to run the yellow.

ahepp 5y ago
The major concern in the OP seems to be left turns hitting pedestrians. Eliminating the left turn over the crosswalk removes this problem. I would argue left turns to cross over the median aren't crossing oncoming traffic, they're merging into traffic going the same direction. Dedicated left turn light phases solve the problem too, but there's a cost to intersection throughput since there's an additional light phase (during which only left-turners on one axis can move). There are certainly a lot of trade offs to be made here with regards to space, cost, and safety.

Sparkyte 5y ago

Probably one of the safest ways to turn left as you have no bi-directional flows to compete against. When in a city and it is a grid I would just do the UPS right turn to make a left. One extra street down, right, right and straight.

exhilaration 5y ago
I feel like (in Manhattan, pre-covid) that would add at least 5 minutes to your trip. More doing rush hour.
- Sparkyte 5y ago
  Well yeah... I wouldn't drive Manhattan funny enough.

dahfizz 5y ago

This sounds like a weird way to implement a jughandle turn. https://en.wikipedia.org/wiki/Jughandle https://en.wikipedia.org/wiki/Jughandle

caspper69 5y ago
It is sort of a jughandle, but the diagrams on wiki don't really do it justice. These exist on major thoroughfares where the destination road is divided. So you make a right and go to the far left lane, then go into a u-turn in the median where you can make a left turn in the desired direction without worrying about crossing oncoming traffic. Here's a link, and if you look at Telegraph Rd. just north of Maple (a few hundred yards from where Jimmy Hoffa was last seen alive), you can clearly see the traffic flow: https://www.google.com/maps/place/Telegraph+Rd+%26+W+Maple+Rd,+Bloomfield+Twp,+MI+48301/@42.5452613,-83.2858446,437m/data=!3m1!1e3!4m5!3m4!1s0x8824b850d128065f:0x735947c9c619db68!8m2!3d42.5448116!4d-83.2848117 https://www.google.com/maps/place/Telegraph+Rd+%26+W+Maple+R...

selimthegrim 5y ago

Also very common in New Orleans.