Could Your GPS Lead You Wrong?

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Harm’s Way

Apparently, even a high-tech GPS device can be misleading. In Victoria, Australia, a South Wales man was pulled over driving the wrong way down a highway, telling police that he was following his GPS instructions. An Ohio woman “turned right” as directed and found herself driving on train tracks, one minute away from an oncoming train. A Senegalese man’s GPS took him on a long drive down a short pier into a lake in Spain.


Not-So-Smooth Operator

Then again, you can never underestimate the power of inaccurate programming. A Belgian woman drove 900 miles out of her way and landed in Croatia instead of her intended destination: the train station in Brussels, a mere 90 miles from her home. She reported that she just kept following her GPS instructions, but it is inconclusive as to whether she entered the correct address.


Technical Difficulty

Aside from a driver’s programming errors, other factors can cause a navigation device to deliver inaccurate route instructions. The principal error pertains to the GPS receiver’s inaccurate time keeping. The on-board computer receives information traveling (theoretically) at light speed from three or more satellites which calculates speed, position and altitude in GPS time, which does not always synchronize with the device’s clock. The result is that calculated distances can drift. The solution? Well, there are two: one is to install an atomic clock in each receiver at a cost of $100,000. But since this option is rather cost-prohibitive, manufacturers have chosen to use some clever mathematics to determine how a GPS detects satellite signals, which in turn, allows the device’s clock to reset.


Time Warp

GPS errors can also be caused by differences in information transmission/receiving speeds or actual signal distortions. The speed of microwave signals from satellites is specific and slightly different from the rate at which a receiver detects those signals, thus allowing for a distance error rate of up to about 9 feet. Atmospheric conditions can distort a signal before it reaches the receiver, as can reflections from large, solid objects or structures. A satellite’s time keeping may also be a little off-kilter, which is why a GPS seeks to use data from at least three satellites to get more consistent updates.



Right On

Consumer-grade navigation device accuracy will likely be improved over time; military use GPS models are already at least ten times as accurate. But while you wait to get your hands on something better, it’s best to read the road signs: if they are written in a foreign language or if they indicate one-way oncoming traffic or trains, follow your nose instead of your GPS navigation system.

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Katherine Stephens

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