Lighting

Restrictions In Road Sign Detection (Speed Limit Information)

Additional symbols on signs for speed limits
The system can only recognize and interpret the additional symbols for wet roads, rain, snow and trucks. Other additional symbols are not detected. The speed limit is displayed without taking account of additional symbols. The additional symbol for wet roads is only taken into account if wiper operation is active. Speed limits that only apply at certain times of day are taken from the navigation data.

Parallel, branching roads or junctions
In the case of signs on roads that are close to the road on which the vehicle is moving, it can occur that the system reacts to speed limits on the adjacent road.

Signs on trucks
Signs attached to trucks can lead to incorrect recognition by the system. This fault occurs in particular with stationary trucks, on overtaking and when driving behind a truck.

Entering / exiting towns
The speed limits on driving through towns are taken from the navigation data. If these data are not up to date, false alarms can occur.

Partially concealed or soiled road signs
If the sign is partially covered by trees, dirt, snow or by trucks, it might not be recognized. Problems can also occur during heavy rain, fog and if the sun is low.

Signs that do not comply with standards
The road signs to be identified must correspond to the standard. General signposts can lead to misinterpretations. The system is unable to distinguish between general signposts and speed limit signs. For example:
- Information panels at border crossings
- Signs for recommended speed
- Military signposts
- Numbering on exit signs
- Maximum weights for bridges
- End of a no-overtaking zone

Speed and distance
If there is a great distance to the sign to be identified and if the vehicle is moving at high speed, it can occasionally occur that a sign is not recognized. The greater these two variables, the more likely that a sign is not recognized. This effect is stronger when driving at night.