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80 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 above four scenarios (percentage increases and decreases Changes to PMT and VMT in IVTT) and compared. The impacts of changes in IVTT on the aggregate activity travel patterns were examined An increase in IVTT decreases the overall PMT (Table 2) by using several measures, including (a) trip frequency, and VMT (Table 3), whereas a decrease in IVTT (b) person-miles of travel (PMT) and vehicle-miles of increases the overall PMT and VMT. As would be travel (VMT), and (c) person-hours of travel (PHT). expected, the PMT and VMT for home-based work trips show the least sensitivity to changes in IVTT. In contrast, the distances traveled for nonwork purposes (especially Changes to Trip Frequency shopping, socialrecreation, and personal business) are affected by transportation level of service. These changes A 10% increase in IVTT decreases the total number of are consistent with intuitive expectations, as the home trips by 1%, and a 25% IVTT increase decreases the and work locations are fixed in the short term. total number of trips by 2.4% (Table 1). A 10% decrease in IVTT increases the total trips by 1.16%, and a 25% IVTT decrease increases the number of trips by 3.1%. In Changes to PHT addition, the frequency of home-based work trips is least sensitive to IVTT changes. The impacts of changes in IVTT on total PHT are pre- Further disaggregating the trip by destination activity sented in Table 4. An increase in IVTT increases the PHT purpose shows that the frequency of trips for for work and decreases the PHT for nonwork purposes socialrecreation, shopping, and personal business is the (especially shopping and socialrecreation), resulting in most sensitive to changes in IVTT. (IVTT affects genera- an overall increase in PHT. A decrease in IVTT reduces tion of activities for these purposes via the accessibility work PHT and increases nonwork PHT, resulting in an measure.) overall decrease in PHT. TABLE 1 Impact of IVTT on Trip Frequency Home-Based Work Home-Based Other Non-Home-Based Overall No. of Trips* % Diff. No. of Trips* % Diff. No. of Trips* % Diff. No. of Trips* % Diff. Base case 3.70 -- 5.58 -- 2.35 -- 11.62 -- 10% increase 3.70 0.08 5.51 1.27 2.29 2.30 11.50 1.05 25% increase 3.71 0.24 5.41 3.05 2.23 5.08 11.34 2.42 10% decrease 3.69 0.22 5.66 1.49 2.41 2.52 11.76 1.16 25% decrease 3.68 0.59 5.80 4.06 2.51 6.83 11.99 3.14 *Number of trips is in millions. TABLE 2 Impact of IVTT on PMT Home-Based Work Home-Based Other Non-Home-Based Overall PMT* % Diff. PMT* % Diff. PMT* % Diff. PMT* % Diff. Base case 54.03 -- 83.34 -- 27.53 -- 164.91 -- 10% increase 54.03 0.01 77.21 7.35 24.76 10.05 156.01 5.40 25% increase 54.03 0.00 69.21 16.95 21.56 21.69 144.81 12.19 10% decrease 53.96 0.13 90.65 8.77 30.91 12.26 175.52 6.43 25% decrease 53.80 0.44 104.02 24.81 37.53 36.30 195.34 18.46 *PMT is in millions of miles. TABLE 3 Impact of IVTT on VMT Home-Based Work Home-Based Other Non-Home-Based Overall VMT* % Diff. VMT* % Diff. VMT* % Diff. VMT* % Diff. Base case 44.84 -- 58.45 -- 22.00 -- 125.30 -- 10% increase 44.85 0.02 54.07 7.50 19.80 10.03 118.71 5.26 25% increase 44.83 0.02 48.40 17.19 17.24 21.64 110.48 11.83 10% decrease 44.81 0.08 63.65 8.88 24.70 12.25 133.15 6.27 25% decrease 44.65 0.43 73.25 25.32 30.04 36.53 147.95 18.07 *VMT is in millions of miles.