A traffic flow map, i.e. a map of the traffic flow levels on the road segments in a road network, is a fundamental quantity in transport planning. Whilst traffic flow maps are a rich source of information about vehicle mobility patterns, they are also costly in terms of time and resources to compute for any reasonably sized road network.

To alleviate this cost burden, we can use empirical trajectory data from GNSS (Global Navigation Satellite Systems) which includes the well-known GPS, as our input data source since they can be acquired with low marginal cost whilst offering extensive spatio-temporal coverage. Click on each city name in the header banner for interactive flow maps computed from trajectory data from that city.

In a preview of these flow maps in the image comparison below, we zoom into 379 trajectories collected in Hannover, Germany. The green circles of the vehicle trajectories can deviate from the road network.

If we move the slider from right to left, the error-prone empirical trajectories are replaced with single flow lines, each with a single traffic flow value. Our innovative flow map visualises intuitively and unambiguously the traffic flow on each road segment.

Details of this innovation based on aligning road segments to the most locally representative segment can be found in the ArXiv preprint arxiv:2406.17500. Any questions about the methodology can be addressed to Tarn Duong tarn(dot)duong(at)gmail(dot)com.