Fleet Telematics API continuosuly computes routes while the vehicle is travelling, to update the ETA. After the initial route planning, call the router again, e.g. every few minutes, providing the GPS trace, to get an updated ETA.
Activate this feature in a calculateroute.json call by &routeMatch=2 and put the trace into the POST body.
Improved ETA (total and per waypoint) because it knows the past (from the actual GPS trace).
driver rest time (computes next legal rest from the time actually resumed from previous rests)
which planned waypoints have been met or skipped so far (from checking the GPS trace)
map matching of the current GPS position is better, because route matcher considers the history
In the re-route requests simply send the trace so far, router does all the rest.
Improved ETA important to notify/alert the end user / receiver upfront on changes.