I’m trying to model an intersection which under existing conditions has 1 LT lane, 4 through lanes and one 1 RT lane on EB and WB approaches. The major road (EB/WB approaches) will be under construction including resurfacing and minor median modifications. The inside through lane and LT’s lanes will be closed during construction; therefore a shared LT/through lane, 2 through lanes and a RT lane will be available during construction. However the existing phasing which includes protected LT’s may or may not remain in place during construction.
I’m trying to model this scenario to demonstrate the operational benefits of changing the signal phasing during construction to split EB/WB phasing. I found out that HCS does not model this scenario; the two phasing options available for a shared LT/through lane are permitted LT or split phases. However, SYNCHRO model this scenario and even produces an HCM report. If you convert the SYNCHRO file into HCS format, a warning appears saying that the LT phasing is inefficient. Does this means that the HCM output produced by SYNCHRO is not reliable? How do I model such scenario with meaningful results? Simtraffic would be a better approach?
If the staging plans calls for a shared thru-left, then I'd say you HAVE to have Split phasing or Permissive phasing. Protected left turns is asking for accidents. It sounds like you're eating up 3 middle lanes total and with that much separation permissive phasing probably isn't a good idea either.
It does not sound smart at all to consider protected left turns for a shared lane. If the left turn volume is that high, give it a left turn only lane, and sign detours for the through traffic as it sounds like demand is high for the through moves. Alternatively, it might be better to prohibit left turns from the mainline (giving detours for the left turns), giving you 3 through lanes each direction on mainline. by eliminating left turn phases and detouring left turn traffic you've allowed the two thru lanes to operate longer than you would otherwise, and can push more traffic in the reduced configuration. I really, really would not recommend protected left turns from a shared lane.
