AbstractCommercial truck crashes cause thousands of fatalities and serious injuries every year in the United States. One aspect of motor‐carrier safety that has received limited attention, both theoretically and empirically, is the safety of new entrant motor carriers. This limited attention is surprising given regulators perceive new entrants as posing substantial safety concerns. This research seeks to fill this void by drawing on generative mechanisms from old institutional theory and population ecology to theorize that new entrants are likely to follow one of two safety trajectories. This complements prior work that has sought to explain safety differences between new entrants and established carriers. To test our theory, we collect longitudinal safety data from the Compliance, Safety, and Accountability program for a large sample of new entrant carriers and fit a series of mixed‐effects models to estimate new entrants' safety trajectories. Our results provide corroborating evidence for our theorized trajectories and identify how one new entrant characteristic, size, affects these firms' safety trajectories.