Buchholz, Nicholas WyethSilberman, Sebastian2025-07-292025-07-292025https://theses-dissertations.princeton.edu/handle/88435/dsp016q182p57cI study the impact that the Denver metropolitan area’s Regional Transportation District (RTD) commuter rail, opened from 2016 to 2020, had on commuting patterns in the region. Specifically, I estimate a dynamic difference-in-differences model centered around the openings of the A, G, and N rail lines, using areas of the region with older light rail transit lines as a control group. Using American Community 5-year panel data from 2011 to 2023 for commuting times and commuting mode shares by census tract and year, I found null effects on these outcomes for the G and N lines and multiple notable results for the A line, which is considered the RTD’s “flagship line.” My work finds that the A line saw mixed success in some of the metrics I evaluated. The A Line was associated with a temporary relief in car congestion in the line’s vicinity; I estimate that it was responsible for an increase in the share of car commuters commuting less than 30 minutes to work of up to 6.8 percentage points following the line’s opening, an effect which later subsided. I also estimate that the opening of the line was actually responsible for a decrease in the public transit mode share among commuters, leading to a decrease in bus commuter mode share of 2.5 percentage points yet an increase in train commuter mode share of 1.4 percentage points, an impact which I attribute to cuts in bus service following the new rail line. This result appears to show potential shortcomings of rail in replacing bus service. In conclusion, I argue that ridership can be increased through transit-oriented development (TOD) along commuter rail lines.en-USPrinceton University Senior Theses