I'm modeling an intersection that has one EB left turn lane. We're trying to determine if if would be better to change the adjacent through lane into a shared through and left turn lane, to provide more capacity for left turns (there are only a slight amount of through vehicles, but we are hesitant to split the intersection).

The Synchro ICU and HCM output both agree that the second configuration is better. Simtraffic through provides almost the same results because the left turning vehicles are all using the left only lane, and not using the shared left and through lane (in the second configuration). I've tried playing around with various inputs, and trying other configurations, but I can't get left turning vehicles to use the second lane. How do I get around this problem?

Hi Rob,

In SimTraffic the vehicles choose their lanes based on lane changing logic. Is there something going on downstream that causes vehicles to favor one lane or the other? For intance, after vehicles make the left turn, do they need to switch lanes due a downstream taper? If this is the case, vehicles may prefer the exclusive left to avoid making this downstream lane change. You can modify the Postioning values for vehicles. This is different in SimTraffic version 6 and 5, so please refer to the appropriate Help file. In both, the details are in the topic "Lane Choice and Lane Changes".

Thanks,

John.

John Albeck
Trafficware

Thank you, I think I figured it out. There are three receiving lanes, two through lanes and a right turn only lane. I thought that the double-left turn lanes would empty into the two through lanes, but instead it appears that the right turn lane and the through lane received them. I adjusted the positioning distances on the receiving link and now, although still reluctant to do so, some cars are using the second left turn lane.

Is there a way to set receiving lanes for left turns? The actual design of the roadway calls for the double left turn lanes to empty into the two through lanes, and it would be better if the model reflected this.

Thanks,
Rob

Hi Rob,

Sorry, you can't control the paths through the intersection. Can you code the right turn with a right turn pocket? This will force the lefts into the throughs.

Thanks,

John.

John Albeck
Trafficware