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## WHAT IS IT?

In this model a number of car drivers move around over crossing streets and find their way from their homes to their working places and back. In the beginning they use the right or left lane of the streets in an arbitrary manner. When they meet an upcoming car on the same lane they do not crash but try to find a way to avoid a crash by changing the lane.

## HOW IT WORKS

At every crossroads the car drivers try to use the turn-off which brings them fastest to their destination. When they encounter an upcoming car, i.e. a conflict between right-hand drivers and left-hand drivers, they find out which lane of the street is used by the majority within their vision-range and decide to switch to driving on the other side of the street and continue their way. If this is not possible they turn on the same patch and continue their way in the opposite direction, deciding at the next crossroad which turn-off brings them fastest to their destination.

## HOW TO USE IT

Currently one can only change the number of cars (traffic density) and the range of vision of the car-drivers.

Moreover it is possible to switch between four decision modes:

* ISING: the probability of solving a conflict by changing the preferred lane is a function of the current overall majority.
* LOCAL MAJORITY: in case of a conflict both cars decide to use the lane which is used by the local majority.
* NORM: the conflicting cars issue norm invocations which are stored in the memories of the conflicting parties and in the memories of car drivers in the local neighbourhood; the memories store up to 30 items, older messages are deleted; they use their memories to decide about a change of their preferred lane in two different modes
* NORM EQ: they just count the norm invocations in favour or right or left or
* NORM HI: they weight the norm invocations in favour of right or left with the strength of the norm invocations, the latter depending on how strong the majority perceptions of the invocators were when they were memorised.

With `randomise?' switched on, each run starts with a random configuration.

## THINGS TO NOTICE

In most cases all car drivers arrive at their destination and find back home, perhaps several times. After some time a majority of drivers use the same lane, either driving on the left or on the right. How big the majority is and how long it takes all cars to arrive at their destinations depends on the traffic density and the range of vision. The simulation stops 20 time steps after the last conflict.

## THINGS TO TRY

In a large number of simulation runs with different combinations of traffic density and range of vision the dependence of the time until all cars arrived at their destinations and the majority on traffic density and range of vision can be determined.

## EXTENDING THE MODEL

It might be interesting how much the behaviour changes when the road network becomes more complicated.

## NETLOGO FEATURES

## RELATED MODELS

Model 3476 by Carl Edwards is about lane changing for overtaking, not about the emergence of left-hand traffic or right-hand traffic as a legal norm.

## CREDITS AND REFERENCES

The model is mentioned in Klaus G. Troitzsch: Can lawlike rules emerge without the intervention of legislators? (submitted to Frontiers in Evolutionary Sociology
and Biosociology).

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