Monday, May 2, 2011

Challenging the Quarter Mile Rule for Pedestrians in D.C.

According to planning literature, pedestrian trips rarely exceed 10 minutes or ¼ mile in distance. Yet, according to the 2009 National Household Transportation Survey (when performing simple linear regression analysis on TRVL_MIN and TRPMILES variables for trips under sixty minutes), the average pedestrian travel time in the District of Columbia is 12.4 minutes and the average trip in more than twice the expected travel distance – 0.58 miles. On average, pedestrians are traveling 2.16 miles per hour. For every extra minute of travel, the average person walks between .031 and .041 miles (with 95% confidence). Therefore, the average person completes roughly one mile in 27 minutes!

Note, there are a few outliers skewing the data. These respondents cover more than two miles in a short period of time, which may be due to athletic activities or collection errors. However, with several respondents, I am 95% confident that for every 10-minute trip, the average distance covered will be between 0.446 and 0.534 miles - well above the quarter mile cut-off. Upon conducting a hypothesis test to confirm a linear relationship between travel distance and time, I reject the null hypothesis at .01 level, however there is a 1% chance that the travel time and distance does not have a linear relationship. The coefficient of determination (R2) is 0.6589, therefore 65.89% of the variation in derived trip time (X) is explained by the regression of travel distance (Y) – trip duration and distance are highly correlated.

The average pedestrian trip in the District is more than double the expected distance proposed by classic planning literature. Pedestrians are moving swiftly, where the average person completes roughly one mile in 27 minutes. Also, the mode share for pedestrian trips is abnormally high – 27% for trips captured in the 2009 National Household Travel Survey. The increase in distance and frequency of walking trips may be, in part, due to the District’s urban nature where it is difficult to own a vehicle and where property values are high – forcing people to live farther from the places they need to visit.