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OCR for page 179
168 I N N O VAT I O N S I N T R AV E L D E M A N D M O D E L I N G , V O L U M E 2
trips from within the North Corridor to the CBD are near northeast more than is shown from the CTPP. The
underrepresented by 5%. Regionally, the model is over- far southwest shows a high amount of CBD-oriented
representing trips to Ohio State University (OSU) by workers, while eastern Delaware County shows a fair
just 3%. There are specific travel markets that are number of CBD-oriented workers.
weak, including a 27% underestimation of tours from
the North Corridor to OSU. Work-tour productions
and attractions are well estimated by the model. Almost HIGHWAY ASSIGNMENT VALIDATION
all markets are represented within 10% of the CTPP
totals. Model validation refers to the comparison of estimated
Figure 2 shows the modeled travel analysis zones with and observed individual highway link loadings and tran-
work-tour destinations in the CBD. Figure 3 shows the sit route boardings. The purpose of model validation is
same for census blocks from the CTPP. While the zones to gauge how accurately the model predicts observed
don't match one-to-one, patterns are reflected fairly base-year travel patterns and to identify potential model
accurately. The near northwest and the second ring east shortcomings. The MORPC model was validated against
are two high-income suburbs that are reflected in both traffic counts that have been processed to represent
maps. The area around the southern circle is OSU, and directional average annual daily traffic for the year 2000.
the small size of the zones in that area potentially The criteria used to assess the adequacy of the model val-
obscures the correlation there (also note the above dis- idation were: percent vehicle miles traveled (VMT) error,
cussion). The model smoothes the employment in the percent VMT root-mean-square error (RMSE), and per-
cent volume RMSE, by facility type and volume group.
Highway assignment validation was geographically
structured by districting schemes--rings, sectors, and
super districts.
The validation by volume group is shown in Figure 4
and Table 4. All volume groups, except 0500, fall below
the maximum allowable percent RMSE. (Maximum
Allowable %RMSE per ODOT Traffic Assignment Pro-
cedures, page 30.)
Table 5 shows validation statistics by facility type.
Total VMT is within 1% of the observed data, and total
volume is within 2% of the observed volumes.
With respect to the geographic districts as shown in
Figure 5, the results demonstrate a validated model with
respect to observed counts by each of the three district-
ing schemes--concentric rings, radial sectors, and super
districts.
FIGURE 2 2000 model work trips to CBD.
250
Model % RMSE
Max % RMSE
200
150
Percent
100
50
0
1, 1 9
2, 2 9
3, 3 9
4, 4 9
5, 5 9
7, 6 9
10 8 0 99
11 0,0 0 99
12 2,5 1 99
13 5,0 1 99
14 7,5 1 99
15 ,0 1 9
16 5,0 2 99
17 35 0 999
,0 5 99
20 9
00
3 500 49
4 500 ,49
5 500 ,49
6 500 ,49
7 500 ,49
8 500 ,49
20 00 ,49
1 ,99
9 00 ,9
1 50 ,4
1 0 9
1 00 ,4
1 0 9
2 00 ,9
55 000 4,9
,0
9,
4,
0 4,
8
2
7
9
00 4
0
3
1
0
0
,
2
,
FIGURE 3 2000 CTPP work trips to CBD. FIGURE 4 % RMSE by volume group.
