  Using turn signals to convey a driver's intention to change lanes provides a
direct and unambiguous way of communicating with nearby drivers. Nonetheless,
past research has indicated that drivers may not always use their turn signals
prior to starting a lane change. In this study, we analyze realistic driving
data to investigate turn signal usage during lane changes on highways in and
around Gothenburg, Sweden. We examine turn signal usage and identify factors
that have an influence on it by employing Bayesian hierarchical modelling
(BHM). The results showed that a turn signal was used in approximately 60% of
cases before starting a lane change, while it was only used after the start of
a lane change in 33% of cases. In 7% of cases, a turn signal was not used at
all. Additionally, the BHM results reveal that various factors influence turn
signal usage. The study concludes that understanding the factors that affect
turn signal usage is crucial for improving traffic safety through policy-making
and designing algorithms for autonomous vehicles for future mixed traffic.
