  Equal access to voting is a core feature of democratic government. Using data
from millions of smartphone users, we quantify a racial disparity in voting
wait times across a nationwide sample of polling places during the 2016 U.S.
presidential election. Relative to entirely-white neighborhoods, residents of
entirely-black neighborhoods waited 29% longer to vote and were 74% more likely
to spend more than 30 minutes at their polling place. This disparity holds when
comparing predominantly white and black polling places within the same states
and counties, and survives numerous robustness and placebo tests. We shed light
on the mechanism for these results and discuss how geospatial data can be an
effective tool to both measure and monitor these disparities going forward.
