How do drivers react to partisan bumper stickers?

Summary

1 Introduction Bumper stickers are unavoidable on American roads. Love them or hate them, but every American driver is familiar with them. They are used to advertise everything from commercial businesses to religious beliefs, and their popularity has spawned several prolific subgenres, including the almost endless variety of political bumper stickers (Case, 1992). These political stickers are sometimes pithy, sometimes profound, and have entered folklore as the ultimate litmus test for any new slogan: ‘it has to fit on a bumper sticker’. But despite being embedded in modern political life, surprisingly little is known about the influence of partisan bumper stickers on the people who see them. This is a particularly important question in the contemporary US, because of the rise of political polarization (Druckman et al., 2019; Iyengar et al., 2019; Kalmoe and Mason, 2022; Klein, 2020; Levendusky, 2009). There is a growing literature exploring how polarized partisan identity can shape individual behavior in increasingly powerful ways, even in settings that are not explicitly political (Engelhardt and Utych, 2020; Kalmoe and Mason, 2022; Mamakos and Finkel, 2023; Webster et al., 2022). We expand this literature by asking about one of these settings. Specifically, does seeing a partisan bumper sticker change people’s driving behavior? This question is relevant for understanding how partisanship affects peoples’ lives in everyday settings (Kalmoe and Mason, 2022), but it also contributes to research on understanding road safety (Balkmar, 2018), symbolism in cars (Gilroy, 2001), and political advertising (Green et al., 2016). We argue that bumper stickers only affect driving behavior if two conditions are met: (1) they are out-partisan stickers, and (2) they are viewed during a negative interaction with another driver. Bumper stickers are irrelevant to driving behavior in the normal course of events, when things are going well; but if a negative interaction occurs with an...