Anomaly Detection in Riding Behaviours : Using Unsupervised Machine Learning Methods on Time Series Data from Micromobility Services

Abstract: The global micromobility market is a fast growing market valued at USD 40.19 Billion in 2020. As the market grows, it is of great importance for companies to gain market shares in order to stay competitive and be the first choice within micromobility services. This can be achieved by, e.g., offering a safe micromobility service, for both riders and other road users. With state-of-the-art technology, accident prevention and preventing misuse of scooters and cities’ infrastructure is achievable. This study is conducted in collaboration with Voi Technology, a Swedish micromobility company that is committed to eliminate all serious injuries and fatalities in their value chain by 2030. Given such an ambition, the aim of the thesis is to evaluate the possibility of using unsupervised machine learning for anomaly detection with sensor data, to distinguish abnormal and normal riding behaviours. The study evaluates two machine learning algorithms; isolation forest and artificial neural networks, namely autoencoders. Beyond assessing the models ability to detect abnormal riding behaviours in general, they are evaluated based on their ability to find certain behaviours. By simulating different abnormal riding behaviours, model evaluation can be performed. The data preparation performed for the models include transforming the time series data into non-overlapping windows of a specific size containing descriptive statistics. The result obtained shows that finding a one-size-fits all type of anomaly detection model did not work as desired for either the isolation forest or the autoencoder. Further, the result indicate that one of the abnormal riding behaviours appears to be easier to distinguish, which motivates evaluating models created with the aim of distinguishing that specific behaviour. Hence, a simple moving average is also implemented to explore the performance of a very basic forecasting method. For this method, a similar data transformation as previously described is not performed as it utilises a sliding window of specific size, which is run on a single feature corresponding to an entire scooter ride. The result show that it is possible to isolate one type of abnormal riding behaviour using the autoencoder model. Additionally, the simple moving average model can also be utilised to detect the behaviour in question. Out of the two models, it is recommended to deploy a simple moving average due to its simplicity.