## 3 Data and Method  
The data source for this study included two travel surveys: the 1994 Portland Activity Survey and the 2011 Oregon Household Activity Survey. These two surveys collected activity diaries of all members of the surveyed households during the survey period, as well as their socio-demographic characteristics. Table 1 presents a select subset of these variableswith descriptions and summary statistics. The 2011 survey involved 4799 households, 11,133 members, and 41,613 trips (in the Portland metropolitan area), while the 1994 survey included 4451 households, 10,048 members, and 129,188 linked trips. The 1994 survey covered two consecutive days, one of which had to be a weekday, while the 2011 survey was a 24 h weekday survey. To compare with the 2011 survey data, only trips made in one weekday were selected in the 1994 survey data. These two surveys both contain sampling weights that correct for the representativeness of each sample. This study used household weights to weight the travel outcome variables. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Name** & **Description** & **Mean** & **Min** & **Max** & **\%** \\ \hline TravelTime & Commuting time in minutes & 24.70 & 1.00 & 119.00 & \\ \hline TripDist & Travel distance in miles & 8.00 & 0.01 & 44.50 & \\ \hline \multirow{2}{*}{Age65 Plus} & Older than 65: No & & & 94.98 \\ \cline{2-6}  & Older than 65: Yes & & & 5.02 \\ \hline \multirow{6}{*}{VEH\_OWN} & Vehicle ownership per HH: 0 vehicle & & & 4.19 \\ \cline{2-6}  & Vehicle ownership per HH: 1 vehicle & & & 27.22 \\ \cline{2-6}  & Vehicle ownership per HH: 2 vehicles & & & 45.65 \\ \cline{2-6}  & Vehicle ownership per HH: 3 vehicles & & & 14.90 \\ \cline{2-6}  & Vehicle ownership per HH: 4 vehicles & & & 5.58 \\ \cline{2-6}  & Vehicle ownership per HH: 5 vehicles or more & & & 2.46 \\ \hline \multirow{2}{*}{Gender} & Gender: Female & & & 46.10 \\ \cline{2-6}  & Gender: Male & & & 53.90 \\ \hline HHSIZE & Count of household members per HH & 2.67 & 1.00 & 8.00 & \\ \hline \multirow{6}{*}{HH\_INC} & Household income level: Poverty & & & 4.34 \\ \cline{2-6}  & Household income level: DK/RF & & & 5.25 \\ \cline{2-6}  & Household income level: lowInc & & & 39.49 \\ \cline{2-6}  & Household income level: midInc & & & 15.63 \\ \cline{2-6}  & Household income level: highInc & & & 35.30 \\ \hline \multirow{2}{*}{Year} & Survey year: 1994 & & & 38.00 \\ \cline{2-6}  & Survey year: 2011 & & & 62.00 \\ \hline \multirow{6}{*}{CBD} & Whether the origin or the destination of a trip is located & & & 11.70 \\ \cline{2-6}  & in the CBD area: Yes & & & 88.30 \\ \cline{2-6}  & Whether the origin or the destination of a trip is located & & & \\ \cline{2-6}  & in the CBD area: No & & & 68.00 \\ \hline \multirow{6}{*}{Peak} & Whether a trip is taken during peak period: non-peak & & 32.00 \\ \cline{2-6}  & Household race: White & & & 90.93 \\ \cline{2-6}  & Household race: Black & & & 2.15 \\ \cline{2-6}  & Household race: Asian & & & 1.06 \\ \cline{2-6}  & Household race: DK/RF & & & 0.86 \\ \cline{2-6}  & Household race: Hispanic & & & 2.47 \\ \cline{2-6}  & Household race: Native American & & & 0.64 \\ \cline{2-6}  & Household race: Other & & & 1.89 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Variables, description, and summary statistics. The unit of analysis for this study was the linked trip instead of the trip. The linked trip is defined according to activities (Survey Methods for Transport Planning [28]). For example, walking to a transit station, traveling in a transit vehicle, and walking from a transit station to the destination are three separate unlinked trips, which comprise a linked trip. A new linked trip takes place only when activity changes. This study focused on commuting trips or Home-Based Work (HBW) trips, which include both trips from home to work and vice versa. Finally, 10,366 HBW trips (3476 trips from the 1994 survey and 6890 trips from the 2011 survey) were selected.