GTUs can be generated in different manners. For instance from direct vehicle measurements (position, time and speed known), based on random processes, or anything in between. Depending on the vehicle generation method, information from the tactical planner of the GTU to generate may be required to obey to the behaviors of the GTU.
The idea is to give the tactical planner the following method:
InitialXVT generateInitialXVT(GTUState gtu, DirectedPoint initialLocation, Speed desiredSpeed, GenerationPolicy generationPolicy)
The GTUState represents everything of the GTU, except that it is not connected to the network. Actual GTU's have to be connected to assure consistency. The DirectedPoint is the location to attempt the generation. The Speed is the speed to attempt. Time to attempt is always 'now'. Finally, the GenerationPolicy indicates which dimension is considered variable, being speed, location, time or none.
The tactical planner returns InitialXVT which contains speed, location, time, and whether the situation can be considered as acceptable. Based on this information, the generator may generate the GTU at the given speed, location and time, or attempt generation with a different policy or later in time.
As an example the generator of MOTUS is described in this framework. Vehicles are first generated in a 'free' manner with randomly determined time, which is 'now'. The location is the location of the generator, and the speed is the speed of the first vehicle downstream on the network. The policy is then none. The tactical planner may lower the speed if the desired speed is lower. If at that speed the headway to the first vehicle downstream is ok, the following information is returned: t='now', x='as input, location of generator', v=min(as input, desired speed), ok=true. Otherwise, ok=false and the rest is not important.
If a vehicle cannot be generated as 'free', it is generated as 'queued', i.e. bounded. Time is still 'now', or some small time later to reattempt if this also fails (i.e. a later event of vehicle generation so still 'now' but in a later moment). The location is the location of the first vehicle downstream on the network, and the speed is the speed of the first vehicle downstream on the network. The policy is then location. Now, the tactical planner will reduce the speed if desired speed is lower, and set the location upstream such that the desired headway at that speed is obeyed. If the returned location is not on the network, ok=false. Even if ok=true, the generator may still delay generation if the location is upstream of the generator.