This report presents the summary of the model results after calibration of activity-based model sub-models and validation of highway assignment and transit assignment procedures. The first sub-section External Station Validation compares the model forecasted trips passing through the external stations against the corresponding targets prepared in an earlier report (ExternalStationComposition.html). The Highway Validation section provides the summary of highway validation by comparing model assigned volume against observed roadway counts. The Transit Validation sections compares the boardings predicted by model against the observed boardings. The last section looks at the vehicle miles travelled (VMT) by all the trips; within, into and out of the Lake Tahoe modeling region.

External Station Validation

The external stations trip composition calibration results are shown in the table below. The creation of the target trip numbers is described in detail in the report ExternalStationComposition.html. The calibration of work trips; for both residents and external workers, has also been detailed in the report ExternalWorkerCalibration.html.

Table 1: External trips by type and gate: Targets
External Gate Work Trips Through trips Resident Day Trips Overnight Visitor Day Trips Day Visitor Trips Total Trips
E1_MtRose 889 245 1,987 625 3,102 6,849
E2_Spooner 1,716 786 4,297 1,352 6,708 14,859
E3_Kingsbury 721 86 1,717 540 2,680 5,743
E4_LutherPass 427 370 379 119 592 1,887
E5_EchoSummit 420 730 1,849 582 2,887 6,468
E6_CA89 1,552 129 2,341 737 3,654 8,413
E7_CA267 1,409 451 2,380 749 3,715 8,704
Total 7,134 2,797 14,950 4,704 23,338 52,923
Table 2: External trips by type and gate: Model
External Gate Work trips Through trips Resident DayTrips Overnight Visitor DayTrips Day Visitors Total Trips
E1_MtRose 1,142 259 1,363 284 4,146 7,194
E2_Spooner 1,646 700 5,000 1,798 4,912 14,056
E3_Kingsbury 842 94 2,114 678 2,414 6,142
E4_LutherPass 56 318 140 158 362 1,034
E5_EchoSummit 470 571 2,432 778 2,690 6,941
E6_CA89 1,180 139 1,782 520 4,002 7,623
E7_CA267 1,300 401 2,241 502 3,658 8,102
Total 6,636 2,482 15,072 4,718 22,184 51,092

The table above shows that the match between the target trips and modeled trips by external station and market segment is close. The details on the sub-model that was calibrated for each of the market segment is presented below.

Highway Validation

In the highway assignment the origin-destination trip demand matrix created from the demand models is assigned (loaded) on to the network. The primary output from the highway assignment step is the traffic flow on each roadway link, commonly referred to as the model volume. This section presents the comparison of the model volume against the roadway count obtained from the count databases of the transportation agencies - Nevada Department of Transportation and California Department of Transportation’s Caltrans Performance Measurement System (PeMS) Data. As a consistency check on the roadway count data and the StreetLight data, the two sources were compared to each other. The initial benefit of this comparison was that it helped unearth an error made in summarizing the count data during the initial compilation of the roadway count data. Using the correctly summarized roadway count data, a comparison was made against StreeLlight counts by computing the R2, across all the links that had a roadway count information (see plot to the right). An R2 value of 0.97 indicates a strong match between the roadway count data (used to validate highway assignment) and Streetlight Data (used to validate external station traffic and composition); thus providing confidence in the count data and the StreetLight data. Only five, out of the twenty-five links that had roadway counts, had a Streetlight Data count deviation of 25% or more from the roadway count. The counts obtained from transportation agencies did not cover some of the regions in the modeling area, especially west shore and east shore. To fill this missing gap, the count from StreetLight Data was used. The link ID for the roadway links where StreetLight Data was used are the following: 145,3068,12135,14493,622,4881,4077,14579,14499,2439. Table 3 presents the overall summary and Table 4 provides the link level detail.

Table 3 Highway validation statistic
Statistic Model Threshold
% RMSE Overall 30.7% Below 40%
Correlation Coefficient 0.93 At Least 0.88
Percent of Links Within Allowable Deviation 82.4% At least 75%

In Table 4 the first four columns are self-explanatory. The column Model Deviation is defined as the Abs(1-Model/Count). Max Deviation is based on criterion developed by 2010 RTP Guidelines. It defined maximum deviation that is acceptable for each link based on the observed count - the larger the observed count, the smaller the acceptable deviation. The last column compares the Model Deviation and the Max Deviation and notes whether the link satisfies the max deviation criterion or not.

Transit Validation

Transit assignment validation compares the observed transit boardings against the model assigned transit boardings. The table below shows the route level comparison and the overall comparison. The overall boardings are very close to the observed boardings; however, at route level there are substantial differences. Matching transit boardings at a route level is challenging problem in a regional model but can be improved by improving the transit network coding and making it consistent across the region, which will also involve updating the highway network. Walk access distance is a significant determining factor for transit use; making its representation more realistic and breaking down large TAZs along the transit use corridor will also help in modeling transit more accurately.

Table 5: Boardings by Route
Route Desc Target Boardings Model Boardings
20 64 10
23 158 185
30 2 0
50 355 21
53 139 367
267 - Highway 267 Route 115 46
53 - Late Night 31 85
53 - LTCC 139 184
89 - TART Hwy 89 Route 155 28
East Shore Express 114 0
ML - TART Mainline 304 1407
ML-WS 75 0
PM TART Night Service 66 131
Total 1715 2465

Vehicles Miles Travelled

Vehicle miles travelled (VMT) is the total distance travelled by all the vehicle trips in the model, it quantifies the amount of travel on a network. These trips are segmented by the following categories:

The VMT target was obtained from StreetLight Data. The target data for number of trips, VMT and the average trip distance for each of the trip categories can be seen in Table 6. The model summary is shown in Table 7. The average trip distance, the VMT and the number of trips match well for the II trips and EE trips. However, for the IE trips, the number of trips and VMT in the model output is marginally higher than the StreetLight Targets. The reason is that the highway count data suggested a higher volume (than Streetlight Data counts) along some of the external stations and the model was validated to those higher counts. During model validation, count data typically takes priority over other data sources such as VMT targets.

VMT Report

Table 6: Target Trip Totals, VMT and Mean Distance
TripCat Num Trips Total VMT Mean Distance
EE Trips 1,399 92,953 66.4
Inside the model area 62,574 44.7
Outside the model area 30,379 21.7
IE/EI Trip 44,543 1,975,821 44.4
Inside the model area 444,052 10.0
Outside the model area 1,531,769 34.4
II Trip 217,731 912,881 4.2
Total 263,673 2,981,655 11.3
Table 7: Model Trip Totals, VMT and Mean Distance
TripCat NumTrip Total VMT Mean Distance
EE Trips 1,269 88,459 69.7
Inside the model area 32,517 25.6
Outside the model area 55,942 44.1
IE/EI Trips 48,582 2,218,405 45.7
Inside the model area 563,418 11.6
Outside the model area 1,654,987 34.1
II Trips 170,087 802,888 4.7
Total 219,938 3,109,752 14.1

Table 8 and Table 9 below shows the target and model summary for the EI (and IE) trips segmented by short-distance external zone trips and long-distance external zone trips (the definition and classification of trips into short-distance and long-distance is described in detail in the report Create External Transportation Analysis Zones). Number of trips and the VMT for each category is compared. It can be observed from the table that the model outputs match the target data reasonably well.

Short and Long External Travel

Table 8: Target IE/EI Trips and VMT (Short vs. Long)
Gate Short-Distance Trips Short-Distance VMT Long-Distance Trips Long-Distance VMT
1 5,963 208,524 40 5,068
2 11,626 432,098 1,162 145,545
3 4,333 91,458 35 15,039
4 1,361 39,766 5 2,099
5 1,975 77,546 2,279 293,647
6 6,386 160,207 1,560 199,655
7 6,452 127,434 1,366 177,735
Total 38,096 1,137,033 6,447 838,788
Table 9: Model IE/EI Trips and VMT (Short vs. Long)
Gate Short-Distance Trips Short-Distance VMT Long-Distance Trips Long-Distance VMT
1 6,865 245,210 68 10,258
2 12,259 441,887 1,094 140,989
3 6,006 148,618 40 18,053
4 700 23,093 16 6,956
5 4,447 189,416 1,920 241,571
6 5,967 179,957 1,510 216,950
7 6,126 147,248 1,564 208,201
Total 42,370 1,375,429 6,212 842,978