Importance of smoothing. In the figure we show an example OD pair with a low number of extracted inter-observation times. The black dots show the original distribution of data consisting of in total 1,609 inter-observation times. The green curve shows the smoothed estimate of the probability density function, while the red vertical line denotes the peak estimate and the blue vertical line denotes the lower bound estimate. As is evident from the figure, the original data fluctuates a lot and the general trend of the data is better visible in the smoothed distribution. Furthermore, our decision rule for the peak now selects the first peak of sufficient magnitude, which is a more reasonable estimate than the even higher peak located around 750 minutes.