Travel Demand Model - OKI

OKI/MVRPC Travel Demand Model – Version 6.0Sometimes the iterative process does not yield a good enough set of friction factors. When thishappens, the final friction factor adjustments are done manually. The values of the estimatedparameters or the statistics of the regression are of no particular interest nor contain anybehavioral information, and for this reason they are not reported here.2.5 Model Calibration ResultsTable 2.1 shows the final estimated and observed average trip length for HBW, HBO and NHBtrips, peak and off peak. The difference between observed and estimated average trip length isof the order of 1%, indicating that the model reproduces observed trip lengths with small error.Trip length is in logsum units, that is, equivalent travel time minutes. Logsum values have beenshifted by a fixed amount (see Table 2.2), to ensure all logsum values are positive; hence thevalues reported do not represent average travel times.Table 2-1 Trip Length Frequency Distribution Statistics, Logsum ImpedanceTripAverage Trip LengthCoincidenceIntrazonal TripsPurpose Observed Estimated % Error Ratio Observed Estimated % ErrorHBWPeak 275.4 276.2 0.3% 0.847 18,291 19,254 5.3%Off Peak 250.4 248.1 -0.9% 0.777 22,718 26,731 17.7%HBOPeak 115.5 116.0 0.4% 0.865 130,247 128,935 -1.0%Off Peak 159.8 162.0 1.4% 0.860 126,758 142,053 12.1%NHBPeak 242.1 241.2 -0.4% 0.801 125,355 127,726 1.9%Off Peak 239.0 238.3 -0.3% 0.897 176,148 171,666 -2.5%Table 2.1 also shows the coincidence ratio, an index that defines how close two distributions areto each other. The coincidence ratio is calculated as follows:CoincidenceRatio =Min(%EstimatedTrips ,% ObservedTrips )HighestLogSumkk∑k = 0 Max(%EstimatedTripsk,% ObservedTripsk),where k indicates each interval of the TLFD function (i.e., the logsum values) and % EstimatedTrips and % Observed Trips are the proportion of estimated and observed trips, respectively, ateach logsum interval. A coincidence ratio equal to 1.0 indicates that the two distributions areidentical.For the OKI/MVRPC observed and estimated TLFD functions, the coincidence ratios areapproximately 0.8 or higher for all purposes, which indicates that the overall shape of theestimated trip length distribution functions closely approximate the shape of their respectiveobserved functions.Figures 2.2 to 2.7 show the observed and estimated trip length distribution functions, usinglogsum as the measure of impedance. Again, note that the purpose of the calibration wasachieved, that is, the estimated TLFD function closely approximates the observed TLFD function.Trip Distribution - Gravity Model Calibration 5