Multilevel road networks such as flyovers and overpasses are built in large cities to solve traffic congestion.

Vehicle drivers relying on GPS navigation who accidentally drive onto a flyover with intention only to proceed on the ground level will face this problem: the GPS navigation system does not realise the vehicle has entered a wrong level and continues to give instructions as if it were on the ground level.

Only after quite a while will the system notice the wrong road level and begin to redirect to a new route.

Present vehicle navigation system that uses GPS with positioning error of 10-30 meters has a long existing problem in determining which road level a vehicle has entered, especially for flyovers parallel to the ground level.

Professor Anthony Yeh Gar-On's research team at the Department of Urban Planning and Design of the University of Hong Kong (HKU) offers a novel solution to this long existing vehicle navigation problem since GPS was used over 20 years ago by instantly identifying whether a vehicle has entered a flyover or is still on the ground level.

The Angle Difference Method developed by the team compares the inclination angle of a vehicle and angles of different road levels stored in a Transport GIS to determine whether a vehicle has entered the ramp of a flyover or still on the ground level.

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