Let’s firstly explain the basic parts of the STM:

1. Transition

In STM concept, the transition is defined as a movement of a single vehicle between two consecutive road segments (links). In one transition, we have two links, origin and destination. It is important to mention that link length depends on the map that you use. For example, OpenStreetMap uses very short links (few meters), while other map providers define one link as all road segments between two junctions.

Examples of two transitions on the road network (Image by: Author)

2. Speed

The second step is the speed calculation. To construct an STM, we compute the speed of every vehicle that travels through the transition. It is important to compute speed on the origin and destination link. We used a harmonic speed because it favors the lower values to extract a better representation of the congestions, but one can experiment with other speed computation methods, like the average or median speed. Here are examples for the GNSS data, but other data sources can be used.

Speed calculation on the transition (Image by: Author)

3. Matrix

The first iteration of the matrix is used to represent the counts of the speeds in one transition. Here is an example of five vehicle routes that pass through a green transition in the picture below. It can be seen that observation time is a very important parameter when computing the STM. If more time passes, the counts will be higher, because more cars will travel through the observed transition.

STM computation (1st part — counting the speed transitions) (Image by: Author)

Here are two most common examples of the STMs for one transition observed in two intervals: 1) from 08:30 h to 15:30 h, and 2) from 15:30 h to 17:30 h:

Examples of the STMs: 1) non rush hour, 2) evening rush hour (Image by: Author)

Now we can work with this! On the first image, origin and destination speeds are placed at the middle with high origin and destination speeds, which can indicate normal traffic with no congestion. On the second image, we can observe that most of the counts are located in the upper left corner with low origin and destination speeds, which can indicate congestion. With this, we have extracted some useful traffic patterns.

You can also observe that origin and destination speeds are represented with the absolute values expressed in km/h. To make the STM more comparable on the city-wide scale, it is important to represent the speeds in their relative form within the range of 0–100…

Continue reading: https://towardsdatascience.com/speed-transition-matrix-novel-road-traffic-data-modeling-technique-d37bd82398d1?source=rss—-7f60cf5620c9—4

Source: towardsdatascience.com