  Driving events, such as maneuvers at slow speed and turns, are important for
durability assessments of vehicle components. By counting the number of driving
events, one can estimate the fatigue damage caused by the same kind of events.
Through knowledge of the distribution of driving events for a group of
customers, the vehicles producers can tailor the design, of vehicles, for the
group. In this article, we propose an algorithm that can be applied on-board a
vehicle to online estimate the expected number of driving events occurring, and
thus be used to estimate the distribution of driving events for a certain group
of customers. Since the driving events are not observed directly, the algorithm
uses a hidden Markov model to extract the events. The parameters of the HMM are
estimated using an online EM algorithm. The introduction of the online EM is
crucial for practical usage, on-board vehicles, due to that its complexity of
an iteration is fixed. Typically, the EM algorithm is used to find the, fixed,
parameters that maximizes the likelihood. By introducing a fixed forgetting
factor in the online EM, an adaptive algorithm is acquired. This is important
in practice since the driving conditions changes over time and a single trip
can contain different road types such as city and highway, making the
assumption of fixed parameters unrealistic. Finally, we also derive a method to
online compute the expected damage.
