How much does expected traffic onGold Rush Parkway drop whenwe add the BRT facility?A. I don’t know. The model is still runningB. 6,765.7 vehicle trips per dayC. Hmmm, actually, traffic increased!D. 6% compared to the “No-Project” scenario
If we implement “Smart Growth”land use policies, can we take Gold RushParkway off our long-range project list?A. But all I have is a traffic model!B. The model says increased density leads to increased tripmaking in all modes. Uh-oh!C. Results suggest the parkway will still be necessary unless the growth is accompanied by robust transit at all times of day.
KEY ISSUES CHOICE MODELING TRIP & TOUR BASED MODELS
Inherent Risk Limitations ofand Uncertainty Modeling Insights, not Answers Precision Scale of Model vs. vs. Accuracy Scale of Question
Insights, not Answers:How do we translate from “Results” to “Insights?”Telling the story is harder than running the model.All numbers are relative!Results must be interpreted based on constraints andlimitations of the models.The story includes the path to the results, not justthe final answers.
Inherent Risk and Uncertainty:How do you think about uncertainty in model results?How robust are your strategies, given certainuncertainty?Become One With Your Data.Especially household and employment forecasts!What makes these results liberal/conservative?
Precision vs. AccuracyHighly Precise. ✦✦✦ ✦Highly Accurate. ✦✦
Precision vs. Accuracy ✦Not as Precise. ✦ ✦ ✦And yet, Accurate. ✦ ✦ ✦ ✦
Precision vs. AccuracyHighly Precise….But Not Accurate! ✦✦ ✦✦ ✦ ✦ ✦ ✦(11,346.5 trips?)
Precision vs. Accuracy Your model is ✦ ✦✦ ✦ extremely precise. ✦✦ ✦✦ ✦✦ ✦ ✦✦ ✦ It may or may not be accurate, as well. ✦✦ ✦ ✦✦ ✦✦ Your job is to ✦ ✦✦ ✦ round liberally, and ✦ ✦ ✦✦ ✦ consider the context!
Limitations of Modeling As modelers, we need to be honest in facing the ways models are inappropriate for the questions at hand. As planners, you need to be aware of model and data shortcomings, so you can make informed decisions.