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Seasonality of Transportation Data

Figure 8

In Figures 8a through 8d, the journey to work travel times for each income quartile is displayed. The journey to work travel times for respondents from below average income households for the most part had travel times that were less than the average. For low income households, some monthly travel times were almost five minutes or 20% less than the total monthly average time. Although there seems to be quite a bit of variance from month to month, the respondents in the third quartile had average travel times closest to the overall monthly average times. Respondents in the highest income quartile had travel times greater than the monthly average-five minutes or 25% higher in some cases.

FIGURE 8a - Low Income Minutes Traveled to Work

In Figures 8a through 8d, the journey to work travel times for each income quartile is displayed. The journey to work travel times for respondents from below average income households for the most part had travel times that were less than the average. For low income households, some monthly travel times were almost five minutes or 20% less than the total monthly average time. Although there seems to be quite a bit of variance from month to month, the respondents in the third quartile had average travel times closest to the overall monthly average times. Respondents in the highest income quartile had travel times greater than the monthly average-five minutes or 25% higher in some cases.

FIGURE 8b - Second Quartile Income Minutes Traveled to Work

In Figures 8a through 8d, the journey to work travel times for each income quartile is displayed. The journey to work travel times for respondents from below average income households for the most part had travel times that were less than the average. For low income households, some monthly travel times were almost five minutes or 20% less than the total monthly average time. Although there seems to be quite a bit of variance from month to month, the respondents in the third quartile had average travel times closest to the overall monthly average times. Respondents in the highest income quartile had travel times greater than the monthly average-five minutes or 25% higher in some cases.

FIGURE 8c - Third Quartile Income Minutes Traveled to Work

In Figures 8a through 8d, the journey to work travel times for each income quartile is displayed. The journey to work travel times for respondents from below average income households for the most part had travel times that were less than the average. For low income households, some monthly travel times were almost five minutes or 20% less than the total monthly average time. Although there seems to be quite a bit of variance from month to month, the respondents in the third quartile had average travel times closest to the overall monthly average times. Respondents in the highest income quartile had travel times greater than the monthly average-five minutes or 25% higher in some cases.

FIGURE 8d - High Income Minutes Traveled to Work

We look at the weighted three year average lines for each quartile in Figure 8e to observe seasonal trends. Except for low incomes which exhibit a bit less variability than the other three quartiles, the income lines seem to follow the same positive and negative pattern of the aggregated line, but with a bit more variation. For example, the highest income quartile shows not only the highest travel times, but the highest peaks (representing longest travel times) in both January and August.

FIGURE 8e - Average Minutes Traveled to Work Based on Income

Figure 8f further illustrates the variability in the data when each income quartile is depicted over the 36 month period (January 1999 to December 2001). Here the month to month variation is striking and frustratingly, peaks and valleys don't occur in the same months for the same quartile of data. This figure is most similar to the results depicted in Seethaler and Richardson (2003) who conclude (as described above in the literature review) that they did not observe seasonal trends or monthly repeatability in travel survey data.

FIGURE 8f - Minutes Traveled to Work Each Month Based on Income in Hampden County, MA

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