Hi

We are modeling a number of Diamond interchanges. Due to the traffic conditions we are modeling we need to be able to accommodate u-turning traffic. I have attached the layout of the junction we are trying to model. The inner bridge section of the junction is extremely short at only 35m long, meaning a short cycle time and low capacity, there are 2 lanes in each direction. The template model does not incorporate this u-turn so we have been experimenting with different junction forms. When I try to include a shared u-turn and put in a nominal flow (25vph) I get an extreme level of queue delay. If I add the same amount of traffic turning left without the u-turn then this delay does not appear, this is using split phasing for all through and left movements, and free rights. There appears to be a tipping point where if the number of u-turners is more than can be accommodated on the bridge e.g. more than 5 in this case, the delay increases massively. The total delay for the left turn lane with 5 u-turners is 5.8s with 6 u-turners this becomes 680s.

Has anyone experience in modeling these specific types of traffic conditions? When I run simtraffic the u-turning traffic does not seem to be obstructed from making the movement.

As usual any guidance anyone has would be much appreciated.

Anoop

Diamond_layout.pdf (21 KB, 27 downloads) Diamond layout

I'm assuming this is split phase, rather than permitted left turn? U-turns are very slow compared with left turns in practice, and under a permitted condition, would need a VERY large gap to complete the maneuver. Is it possible to consider roundabouts at the locations?