Simulation/Why Vehicles are teleporting
When running a simulation, one may encounter the following warning:
Warning: Teleporting vehicle '...'; waited too long, lane='...', time=....
What does it mean?
The following circumstances may force the simulation to "teleport" a vehicle:
- the vehicle stood too long in front of an intersection (message: "...'; waited too long, lane='...")
- the vehicle has collided with his leader (message: "...'; collision, lane='...")
Waiting too long, aka Grid-locks
In the case a vehicle is standing at the first position in front of an intersection, SUMO counts the number of steps the vehicle's velocity stays below 0.1m/s. These steps are the "waiting time". In the case the vehicle moves with a larger speed, this counter is reset. In the case the vehicle waited longer than a certain threshold value (default 300 seconds), the vehicle is assumed to be in grid-lock and teleported onto the next free edge on its route. The threshold value can be configure using the option --time-to-teleport <INT> which sets the time in seconds. If the value is not positive, teleporting due to grid-lock is disabled. Note that for vehicles which have a stop as part of their route, the time spent stopping is not counted towards their waiting time.
There are different reasons why a vehicle cannot continue with its route. Every time a vehicle teleports due to grid-lock one of the following reasons is given:
- wrong lane: The vehicle is stuck on a lane which has no connection to the next edge on its route.
- yield The vehicle is stuck on a low-priority road and did not find a gap in the prioritized traffic
- jam The vehicle is stuck on a priority road and there is no space on the next edge.
Unfortunately, grid-locks are rather common in congested simulation scenarios. You can solve this only by improving traffic flow, either by correcting junction priorities, traffic light timings or the traffic demand (route files).
Also, besides plain grid-locks, the imperfection of the lane-change model sometimes leads to a situation where two vehicles try to get to the other lane, and each vehicle is blocking the other one. The simulation behaves as described earlier. An additional possibility to "solve" this is to allow vehicles to be swapped - they are exchanged. To enable this possibility, use the option --lanechange.allow-swap.
Though SUMO uses a collision-free model, collisions have been detected. As they yield in an undefined state of the simulation, a vehicle teleportation is performed for solving them.
What is happening while a vehicle teleports
A teleported vehicle is removed from the network. It is then moved along its route, but no longer being on the street. It is reinserted into the network as soon as this becomes possible. While being teleported, the vehicle is moved along its route with the average speed of the edge it was removed from or - later - it is currently "passing". The vehicle is reinserted into the network if there is enough place to be placed on a lane which allows to continue its drive.