A tight urban diamond interchange is one where the two intersections are so close together that the left turn lanes overlap like this:
(https://i.imgur.com/M9PC3ij.png)
One simple change that greatly improves capacity is to have the left turn lanes swapped like this:
(https://i.imgur.com/GneYh13.png)
This allows left turns to be made in both directions from the arterial to the freeway simultaneously.
A further improvement is to put the left turn lanes all the way on the left in a grade separated version of a Continuous Flow Intersection.
(https://i.imgur.com/sZEG0Nx.png)
2 of these have been built in San Marcos, TX on I-35. In both cases, they simply adapted the existing Texas U-turns to serve as the displaced left turn lanes
Hopefully they get incorporated in more places
Quote from: kernals12 on May 12, 2022, 11:59:45 PM
A further improvement is to put the left turn lanes all the way on the left in a grade separated version of a Continuous Flow Intersection.
(https://i.imgur.com/sZEG0Nx.png)
2 of these have been built in San Marcos, TX on I-35. In both cases, they simply adapted the existing Texas U-turns to serve as the displaced left turn lanes
Specifically–for those interested–they are at TX-80 (Exit 205) and Loop-82 (Exit 206). The latter is one-sided, meaning only one direction of the cross-road has its left turn lane displaced.
So the difference between this and a DDI is that the rams don't extend as far laterally from the freeway, meaning that this is useful in tight places where a DDI is not possible?
Quote from: thspfc on May 13, 2022, 12:23:37 PM
So the difference between this and a DDI is that the rams don't extend as far laterally from the freeway, meaning that this is useful in tight places where a DDI is not possible?
Additionally, in a DDI, the through lanes also move to the left.
Quote from: kernals12 on May 12, 2022, 11:59:45 PM
One simple change that greatly improves capacity is to have the left turn lanes swapped like this:
(https://i.imgur.com/GneYh13.png)
This allows left turns to be made in both directions from the arterial to the freeway simultaneously.
This configuration was used at the I-4 and FL 436 interchange north of Orlando while they were building the SPUI that's currently there. It's a bit hard to capture on Street View, but you might be able to see how it worked here (https://goo.gl/maps/BNwCwhjirTTzAM5Q8) if you go back in time to late 2019-early 2020.
Unfortunately, they missed the opportunity to improve traffic flow; The signal timing and phasing was the same as if it was a standard tight diamond. It was pretty aggravating, but I understand not spending the resources to develop a new signalization plan for a temporary situation.
Quote from: kernals12 on May 12, 2022, 11:59:45 PM
One simple change that greatly improves capacity is to have the left turn lanes swapped like this:
(https://i.imgur.com/GneYh13.png)
This allows left turns to be made in both directions from the arterial to the freeway simultaneously.
I want this set up at this interchange so bad. It would not even be that difficult for INDOT to implement.
https://goo.gl/maps/kpL5xCEN5MiKWAhB8
Quote from: kernals12 on May 12, 2022, 11:59:45 PM
One simple change that greatly improves capacity is to have the left turn lanes swapped like this:
(https://i.imgur.com/GneYh13.png)
This allows left turns to be made in both directions from the arterial to the freeway simultaneously.
This would probably be a good idea at US 69 and 151st Street in Overland Park, Kansas, except with the lanes on the arterial road being doubled. (Here: https://goo.gl/maps/SRcgdDZqi7YXYpXG6 )