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Global Positioning System (GPS)

Last Updated: Nov 12, 2015

What New Drivers Need To Know About How GPS Works:

GPS (Global Positioning System) is a constellation of 24 or more satellites flying 20,350 km above the surface of the Earth. Each one circles the planet twice a day in one of six orbits to provide continuous, worldwide coverage, in order to tell you exactly where you are. By "where you are", it means as in a spot on a map. GPS generally will not tell you if you are "at your Mom's house", "up a creek without a paddle", or "in la-la land".

And here is a TOTALLY sweet GPS educational poster (PDF format).

What Is GPS?

The GPS Master Control Station tracks the satellites via a global monitoring network and manages their health on a daily basis. Ground antennas around the world send data updates and operational commands to the satellites. The Air Force launches new satellites to replace aging ones when needed. The new satellites offer upgraded accuracy and reliability. If you are using GPS in your truck for navigation, (and we know you are. It's the 21st Century), and it guides you into a river, or a swamp, or a Twinkie factory, you are NOT allowed to blame the GPS. You still have to plan your trip properly and be aware of your surroundings.

Advice On Choosing and Using A GPS Device For Trucking:

It is recommended that you choose a GPS unit specifically designed for commercial drivers. Generally, they will provide you with information not normally available on "pedestrian" units". It should include little things like route restrictions, low over-passes, missing bridges, etc.

Plan ahead: CMV-specific GPS's allow you to enter all relevant information not only about your destination, but also your vehicle, ie: vehicle size, axle weights, any hazardous materials you are transporting, etc.

Again, a good GPS is not necessarily going to account for EVERY condition that you might encounter on the road. You still have to pay attention to traffic signs and advisories. You know how tall your truck is. 11' 8" means 11' 8", not "Looks fine. It'll probably make it."

Technical, Jargony GPS Details:

1. GPS satellites broadcast radio signals providing their locations, status, and precise time from on-board atomic clocks.

2. The GPS radio signals travel through space at the speed of light (c), more than 299,792 km/second.

3. A GPS device receives the radio signals, noting their exact time of arrival , and uses these to calculate its distance from each satellite in view.

To calculate its distance from a satellite, a GPS device applies this formula to the satellite's signal: distance = rate x time, where rate is (c) and time is how long the signal traveled through space.

The signal's travel time is the difference between the time broadcast by the satellite and the time the signal is received (t2).

4. Once a GPS device knows its distance from at least four satellites, it can use geometry to determine its location on Earth in three dimensions.


Commercial Motor Vehicle

A CMV is a vehicle that is used as part of a business, is involved in interstate commerce, and may fit any of these descriptions:

  • Weighs 10,001 pounds or more
  • Has a gross vehicle weight rating or gross combination weight rating of 10,001 pounds or more
  • Is designed or used to transport 16 or more passengers (including the driver) not for compensation
  • Is designed or used to transport 9 or more passengers (including the driver) for compensation
  • Is transporting hazardous materials in a quantity requiring placards


Transportation Worker Identification Credential

Truck drivers who regularly pick up from or deliver to the shipping ports will often be required to carry a TWIC card.

Your TWIC is a tamper-resistant biometric card which acts as both your identification in secure areas, as well as an indicator of you having passed the necessary security clearance. TWIC cards are valid for five years. The issuance of TWIC cards is overseen by the Transportation Security Administration and the Department of Homeland Security.


Driving While Intoxicated


When a violation by either a driver or company is confirmed, an out-of-service order removes either the driver or the vehicle from the roadway until the violation is corrected.

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