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?

# Reasons

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 (or all the vehicles before it have a scheduled stop), 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. Note that for vehicles which have a stop as part of their route, the time spent stopping is not counted towards their waiting time.

If there is enough space on the subsequent edge of the vehicle's route, the vehicle will be directly assigned (teleported) to the respective available space. Vehicle insertion will use depart method "free" (anywhere on the lane with the least traffic) and attempt to insert the vehicle with it's maximum allowed speed. The insertion space must allow for all necessary safety gaps of the vehicle itself and it's follower vehicle, though the speed may be reduced if it helps with insertion.

If the vehicle cannot be inserted immediately,it will be held outside the road network in a special 'teleporting-buffer' and (virtually) traverse the next edge with the average speed of that edge (minimum m/s). After this virtual travel time has passed, the next attempt at re-inserting the vehicle into the network is made one edge further along it's route. This procedure repeats until the vehicle has been re-inserted or the end of the route is reached. In the latter case, the vehicle is removed from the simulation. While the vehicle is in the teleporting buffer it remains invisible.

The threshold value can be configure using the option --time-to-teleport <INT> which sets the time in seconds.

Note

Setting --time-to-teleport to a negative value, disables teleporting due to gridlock.

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.

Related options are

- --time-to-teleport.highways: teleport earlier when stuck on the wrong lane of a road with speed above 19.167 m/s
- --time-to-teleport.highways.min-speed: configure threshold for above option
- --time-to-teleport.disconnected: teleport earlier when the route is disconnected

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. There are two common causes of this:

- Motorway weaving sections (combined on- and off-ramps). This can be solved with additional connections
- Vehicles inserted on the wrong lane close to an intersection with turning lanes. This is best solved by setting the vehicle attribute `departLane="best"` to ensure that vehicles are inserted on the correct lane for following their route.

## Collisions

By default, SUMO uses a collision-free model. However, due to bugs, network problems or deliberate configuration, collisions may occur. The default behavior of SUMO is to immediately teleport the rear vehicle onto the next edge of it's route (or remove it, when already on it's final edge). This behavior can be configured to avoid or delay teleporting.

To avoid collisions, observe the simulation sumo-gui at the location and time of the collision. Check if some of the that may cause a collision are present in your network.

# 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. Consequently a vehicle may teleport multiple times within one simulation.

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