Despite a plethora of research examining commercial motor vehicle (CMV) crash risk as a function of time of day, there are few studies that have included objective measures of exposure. The purpose of this study was to use carrier-owned crash and electronic logging device (ELD) data to assess CMV crash rates and, as a function of time of day, using the amount of driving time in each hour as a measure of exposure. This study used the recently completed the Hour-of-Service (HOS) Rules Impact Analysis (under agency review), which contained crash and driver duty status data from 11 carriers with 36,000 crashes and ELD data from over 134,000 drivers over 21,639,182 log-days. The dataset included carrier descriptive information, detailed crash variables, driver log variables, and driver information. Three analyses were performed: crash rate by hour of day, crash rate by daytime vs. nighttime period, and crash rate by morning rush hour, evening rush hour, and non-rush hour periods. Results showed that CMV crash rates per 1 million driving hours were highest at nighttime in the 9:00 p.m. hour, 11:00 p.m. hour, and between 2:00 a.m. and 7:00 a.m. This study also provided some explanation for the inconsistencies in previous results regarding the effect of time of day on CMV crash risk related to operational differences among carriers.