turn-restrictions.md

How to work with Turn Restrictions

GraphHopper supports turn restrictions. Turn restrictions are crucial for correct vehicle navigation and help to avoid forbidden turns.

Without turn restrictions the route will look like:

With turn restrictions it is:

To enable turn restrictions for a profile set the turn_costs configuration like this:

profiles:
  - name: car
    turn_costs:
      restrictions: [motorcar, motor_vehicle]
    ...

When using the Java API you can create the encoding manager like:

DecimalEncodedValue speedEnc = VehicleSpeed.create("car", 5, 5, true);
DecimalEncodedValue turnCostEnc = TurnCost.create("car", maxTurnCosts);
EncodingManager encodingManager = new EncodingManager.Builder().add(speedEnc).addTurnCostEncodedValue(turnCostEnc).build();

Where maxTurnCosts=1 means the turn can either be legal or forbidden.

To enable turn restrictions when using the 'speed mode' additional graph preparation is required, because turn restrictions require edge-based (vs. node-based) traversal of the graph. You have to configure the profiles for which the graph preparation should be run using e.g. profiles_ch, just like when you use the 'speed mode' without turn restrictions.

You can also specify a time penalty for taking u-turns in the profile (turning from one road back to the same road at a junction). Note, that this time-penalty only works reasonably when your weighting is time-based (like "fastest"). To use u-turn costs with speed mode you need to specify the time penalty for each u-turn in the turn_costs configuration: u_turn_costs: 60. See config-example.yml for further details regarding these configurations.

To disable the 'speed mode' per request you can add ch.disable=true and choose the value of u_turn_costs freely in the request.

While OSM data only contains turn restrictions, the GraphHopper routing engine can also deal with turn costs, i.e. you can specify custom turn costs for each turn at each junction. See this experimental branch.

Conditional turn restriction are supported. For example, the following no left turn restriction concerns only bus:

type=restriction
restriction:bus=no_left_turn

Another example, using the except tag, means only bicycle are allowed to turn left:

type=restriction
restriction=no_left_turn
except=bicycle