Speed, TTC, and yPET are measured from the trajectory data collected at all 19 roundabout merging zones (over 23,000 individual road users) and presented in this section. All dependent variables are measured at the individual road user level.
Overall, speed is found to be normally distributed at each site for each movement. Comparing hourly flows versus speed, it is clear that increased traffic is associated with lower speeds, as illustrated in Figure \ref{fig:hourly_speed}. It can also be seen that the Swedish sites have significantly reduced speed, even after controlling for effects of congestion, as measured by traffic volume. Figure \ref{fig:hourly_speed} also demonstrates that the selected sites have, from one hour to the next, roughly comparable traffic demand patterns, although variation is present from hour to hour at the same site (as is expected). Given that the recorded speeds seem to vary based on movement types, speed measures are plotted continuously as a function of space for all four movements in a merging zone, as proposed and first demonstrated in \citep{St_Aubin_2013b}:
vehicles travelling through the merging zone on the roundabout ring exclusively,
vehicles leaving the roundabout via an exit lane,
vehicles entering the roundabout via an approach lane, and
vehicles entering the roundabout via an approach lane and exiting via the next exit lane.
For example, a road user wishing to turn right at a roundabout only needs to travel across a single merging zone i.e. following a single movement type (4) through this merging zone. However, a road user wishing to make a through movement at the same roundabout must cross two successive merging zones following one movement type (3) through the first merging zone followed by a second movement type (2) through the second merging zone. In the same way, a left turn at a roundabout corresponds to movement (3) followed by one movement (1), and finally one movement (2). Finally, a U-turn or a turn at a roundabout with more than four approaches will follow movement (3) followed by multiple movements (1), and finally one movement (2).
The observed speed profiles of road users travelling along these movements are illustrated in Figures \ref{fig:speed_profile_qc} and \ref{fig:speed_profile_se}. A similar overall reduction in speed is noted at the Swedish sites, although this discrepancy is found to be most pronounced for movement type (4). Furthermore, the average approach speed just ahead of each approach yield line also appears to be lower at the Swedish sites.