How "Sharp Turn" angles defined in HERE routing and map guidance?

How "Sharp Turns" classified in HERE routing and navigation?

Symptoms
--------

Customers may report one or more of the following:

A junction is classified as a medium sharp or very sharp turn and the reason is unclear.
Navigation guidance identifies a turn as sharp even though it appears to be a normal intersection.
Different sharp-turn classifications are observed for similar turn angles.
Questions about driver-side versus passenger-side turn thresholds.
Requests for the exact turn-angle ranges used by HERE routing and navigation.

Answer
------

HERE uses sharp-turn classifications to identify turns that may be difficult to navigate, especially for larger vehicles.

There are two sharp-turn categories:

Very Sharp Turn: A turn that is very difficult or may even be impractical for long trucks to perform safely.
Medium Sharp Turn: A turn that is generally feasible for long trucks but requires the driver to slow down considerably.

Sharp-turn thresholds are defined from a right-hand-side driving perspective. For left-hand-side driving countries, the thresholds are applied symmetrically by swapping the passenger side and driver side.



### Sharp Turn Angle Thresholds

| Threshold | Turn Angle Range when turning to FC5 | Turn Angle Range when turning to FC4 or greater |
| --- | --- | --- |
| Medium Sharp Passenger-Side Turn | N/A | >75° |
| Very Sharp Passenger-Side Turn | >80° | >95° |
| Medium Sharp Driver-Side Turn | >80° | >100° |
| Very Sharp Driver-Side Turn | >95° | >120° |
| Driver-Side U-Turn on Single Link | 180° | 180° |

### Important Note

The thresholds include an approximate 5° tolerance to compensate for limited precision in road geometry map data. This prevents common perpendicular junctions from being excluded due to minor geometry inaccuracies.

For example, a very sharp right turn is classified at approximately 95° rather than requiring an exact right-angle measurement.

Root Cause
----------

Turn classifications depend on several factors:

1. The angle between the incoming and outgoing road segments.
2. The Functional Class (FC) of the road being entered.
3. Whether the turn is on the driver side or passenger side.
4. The driving convention of the country (right-hand-side or left-hand-side driving).

As a result, similar-looking junctions may receive different classifications.

Impact
------

Understanding these thresholds helps customers:

Validate routing and navigation results.
Understand truck routing behaviour.
Interpret sharp-turn guidance correctly.
Differentiate expected routing behaviour from map-data or routing issues.

Expected vs. Unexpected Behaviour
---------------------------------

### Expected Behaviour

Turns are classified according to the documented angle thresholds.
Medium sharp turns indicate turns that remain feasible for long trucks but require significant speed reduction.
Very sharp turns indicate turns that are extremely difficult or potentially infeasible for long trucks.
Left-hand-side driving countries use the same model with driver-side and passenger-side directions mirrored.

### Unexpected Behaviour

Assuming the same driver-side and passenger-side interpretation in all countries.
Ignoring Functional Class (FC) differences when validating turn classifications.
Treating threshold-based sharp-turn classifications as routing defects when they match the documented model.

Recommended Actions
-------------------

1. Determine whether the road network uses right-hand-side or left-hand-side driving.
2. Identify the Functional Class (FC) of the road being entered.
3. Measure the turn angle relative to the incoming road segment.
4. Compare the result against the sharp-turn threshold table.
5. Validate whether the observed behaviour matches the applicable medium sharp or very sharp turn category.

Products / Platform
-------------------

HERE Routing
HERE Navigation
HERE Map Data
Truck Routing
* Junction Turn Classification Logic

Keywords / Tags
---------------

sharp turn, medium sharp turn, very sharp turn, turn angle threshold, driver-side turn, passenger-side turn, truck routing, navigation guidance, routing behaviour, FC4, FC5, functional class, junction angle, u-turn, turn classification, road geometry tolerance