A tight urban diamond interchange is one where the two intersections are so close together that the left turn lanes overlap like this:
One simple change that greatly improves capacity is to have the left turn lanes swapped like this:
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.
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