2 Methods
UTA provided time point data for all trips on the UVX system during the summer of 2019. During this period, the TSP requesting threshold was set at three different levels:
- June 10 through July 12 and after August 12: 2 minute threshold
- July 15 through July 26: no TSP
- July 30 through August 9: TSP always requested
We calculated the headway between successive UVX trips at each stop, as well as the cumulative dwell time of all stations along the route to that point. To control for omitted variables, we limited our analysis to the periods between 7 AM and 8 PM when the system runs at a 6-minute headway. Time points within these periods are considered “AM Peak” if occurring between 7 and 9 AM, or “PM Peak” between 4 and 6 PM. We also discard timepoints in south Provo where UVX runs on a one-way circulating loop.
tar_load(period_change_table)
period_change_tableStandard statistical tests — such as the student’s \(t\)-test or
ordinary least squares regression models — are designed to ascertain the
significance of a statistic at the mean of the distribution. In this
application, we are less concerned with the mean deviation in headway, and are
instead interested in whether TSP is able to reduce the lateness of buses that
already have substantial deviation from their programmed headway. Further, a bus
that is delayed from its intended headway may shorten the subsequent headway due
to “bunching.” Consequently, we employ conditional quantile regression
(Koenker & Hallock, 2001) to estimate the effect of TSP requesting threshold on
headway deviation at multiple percentiles of the distribution. This is
done with the quantreg package for R (Koenker, 2020; R Core Team, 2021)
Raw data and complete analysis code are available in a public GitHub repository.