Comparative Analysis of Daytime and Nighttime Crashes in the City of Yuma, Arizona

Abstract: Traffic crashes are a significant public safety concern worldwide, leading to fatalities, serious injuries,
and property damage. Crash statistics and research consistently show that nighttime crashes tend to be
more severe than those during the day, due to reduced visibility, driver fatigue, and an increased incidence
of impaired driving. This study analyzes daytime (6:00 am to 5:59 pm) and nighttime (6:00 pm to 5:59
am) crashes in the city of Yuma, Arizona, identifying patterns, trends, and key factors contributing to their
crash severity. For this purpose, crash data from the most recent nine years between 2015 and 2023 were
retrieved from ADOT’s Arizona Crash Information System (ACIS). Statistical methods, including the
chi-square test, Z-test of proportions, and odds ratio (OR), were used to investigate several factors
affecting crash injury severity, such as crash characteristics, at-fault driver characteristics, and
environmental conditions. The preliminary analysis showed that 76% of all crashes occurred during the
daytime, while nighttime crashes, making up the remaining 24%, were associated with a higher fatality
rate. Specifically, 63% of the total fatalities occurred during nighttime crashes, compared to 37% during
the day. Results from OR revealed that rear-end and angle collision crashes had more than three times the
odds of experiencing a severe crash at nighttime than during the day. Similarly, the odds of a severe left-
turn crash occurring at nighttime were about 1.5 times more than during the day. The Z-test of proportions
comparing the daytime and nighttime DUI (driving under the influence) crashes revealed a significant
difference in the proportions of severe DUI-related crashes between the two periods (Z-test statistic =
31.68). The analysis provides compelling evidence of an increased likelihood of severe DUI-related
incidents occurring at nighttime. The study findings highlight the increased risk of severe crashes and
DUI incidents at nighttime, emphasizing the need for stricter enforcement, enhanced road safety
measures, and improved lighting conditions in high-risk areas.