Self-Inertial Navigation Limitations

The limitations of the self-inertial portion of the navigation system (the gyro and the vehicle speed signal) can cause discrepancies between the vehicle's actual position and the indicated vehicle's position (GPS vehicle position).

The following circumstances may cause vehicle positioning errors:

• Moving the vehicle with the engine stopped and the vehicle stopped, such as by ferry or tow truck, or if the vehicle is spun on a turn table.
• Tire slippage, changes in tire rolling diameters, and some driving situations may cause discrepancies in travel distances. Examples of this include:
  • Continuous tire slippage on a slippery surface
  • Driving with snow chains mounted
  • Abnormal tire pressure
  • Incorrect tire size
  • Frequent lane changes across a wide highway
  • Very bumpy roads
• Tolerances in the system and map inaccuracies sometimes limit how precisely the vehicle's position is indicated. Examples of this include:
  • Driving on roads not shown on the map (map matching is not possible)
  • Driving on a road that winds in one direction, such as a loop bridge, an interchange, or a spiral parking garage
  • Driving on a road with a series of sharp hair-pin turns
  • Driving near a gradual highway exit or transition
  • Driving on one of two close parallel roads
  • Making many 90 degree turns