Traffic waves
Because of the displacement based on the deviation from the assumed normal travel time, the visualization shows clearly that traffic jams can move in waves. These waves move backwards, opposite of the driving direction of the cars.
The Netherlands full view
Visualization
This visualization shows travel time for road segments over time. Roads that have missing data at a certain point in time are gray, roads that do have measurements have a color range from blue to red to white: small deviation, medium deviation and large deviation from assumed normal travel time respectively. Moreover, road segments change in width based on the deviation from the assumed normal travel time. Finally, road segments are displaced orthogonally initially based on deviation from the assumed normal travel time for that road segment, but then tilted so that road segments with identical geographical coordinates remain connected.
Method
Traveltime data has been downloaded from the NDW website. This visualization is not based on GPS coordinates from cars, speed of cars, or the flow of cars, but rather the time it takes from one measurement point on the road to the next measurement point. For every minute of data, the travel time is compared to the assumed normal travel time. The assumed standard travel time for road segments is calculated by taking the mean of a selection of the lowest measured travel times for that road segment, ignoring missing data. These are usually measurements from the nighttime, as there are mostly no traffic jams then, and the travel times on these road segments are the shortest. Missing data up to 10 minutes is filled with interpolated values. Outliers of more than 3 times the standard deviation have been replaced by the mean of its direct neigbors.