I'm calibrating a congested freeway corridor in Southern California, and I've adjusted link speeds, lane capacities, turning speeds, and headway factors on links and at ramp junctions in Synchro. I'm trying to match travel times and average speeds from tach runs.
Does anyone have experience tweaking driver and vehicle parameters in SimTraffic for such a situation (experienced and aggressive freeway drivers; 10% heavy vehicles)? [The SimTraffic Help file is quite useful; but there are a lot of parameters that can be changed, and I'd like to narrow them down.]

Diane Jacobs, P.E.
Caltrans District 7

Hi Diane,

You are correct, this can be rather difficult since each case can be case dependent. Or, in your case, driveres in Southern Cal may operate different then other parts of the country.

It sounds like you've adjusted the items that should be tried first. Many factors I would not touch. But, in the Driver Parameters, you might adjust these factors (if I don't mention them, then they probably do not apply):

* Speed Factor. If you have a speed study, you could adjust these. The value is the speed percent that drivers will operate. For instance, a driver type 1 will drive at 0.75 times the input link speed under freeflow conditions.

* Headways. Probably won't touch these (so why am I mentioning it). This is related to the Headway Factor in the Synchro Lane window. These values will be multiplied by the Headway Factor to adjust the saturation flows. You probably need to reduce the Headway Factors for freeway segments and it sounds like you have done this. Also note that the Headway Factor for a bend node or an external link is shown in the Link Properties window of Synchro.

* Positioning Distance. You might need to adjust these values since they control positioning. This value indicated how far back a vehicle will start to position for a downstream turn. I don't mean to be vague on this, but it honestly is some trial and error to meet your situation.

* Positioning Advantage. This is related to the above. For instance, driver 1 has a distance of 1500' and an advantage of 15.0 vehicles. This means at 1500', they will start to change lanes UNLESS there are 15 fewer vehicles in their current lane when compared to the target lane. Increasing this number would cause them to change lanes more often (they'll accept higher numbers in the target lane).

* Mandatory Factor, Free. This controls how far down a link a vehicle will continue to travel until they reach a MANDATORY lane change. When they get to this point, they must make the lane change. The higher this factor, the further down the link they will travel for this point. There is a diagram of this in the SimTraffic Help.

I hope this helps. Maybe some users will weigh in on this topic also with their experiences.

- John.

John Albeck
Trafficware