The purpose of this article is to examine the various technologies used for vehicle tracking as applied to fleet management. Andy Harris, Technical Director of datatrakSA, takes us through the key issues.
To facilitate management of a fleet of vehicles, some or all of the following information is required:
1. Vehicle position.
2. Current speed.
3. Trips made.
4. Distance travelled.
5. Maximum speed.
6. Start time.
7. Stop time
8. Route followed.
9. Route deviation
10. Entry and exit from go/no-go areas.
11. Entry and exit from predefined areas.
12. Activation of vehicle sensors (doors open/ closed etc)
13. Fuel consumed.
14. Engine revs applied.
15. Acceleration
16. Deceleration.
17. Driver
Items 1-12 can be provided by a vehicle tracking system associated with a resource management system, whilst items 13-17 can be provided by a vehicle on-board computer or tacograph system.
In simple terms vehicle tracking systems have two distinct parts, one is the technology used by the vehicle to locate itself and the second is the technology used to pass that information back to the point where the data is to be used.
Location systems
Satellite GPS - The vehicle carries a small antenna that receives signals from constellations of satellites originally put in place by the American military for their own use. The vehicle can calculate its position if it can 'see' at least three satellites. This can be done anywhere on the earth's surface.
The position calculated can, however, be compromised by the vehicles' inability to 'see' enough satellites due to buildings or other physical objects obscuring the view of the sky.
The position calculated will have an inherent error described as 100 m RMS meaning a peak error of 141 m. This is due to a deliberate 'wobble' put on the data from the satellites by the American military. There are techniques available to 'calculate out' the error using fixed stations generating differential data, this however is rarely applied to vehicle tracking systems.
Terrestrial systems - Terrestrial positioning systems use a number of fixed transmitters covering an area with signals. The effect is to lay down a coordinate grid over an area which can be many thousands of kilometres in size. The vehicle system receives the signals from the transmitters and, by means of time and phase evaluation, can calculate its position.
The advantages of a terrestrial positioning system are:
q Accuracy - a position can be calculated to within one metre.
q The system is unaffected by building and will still position accurately in 'concrete canyons'.
q The system is not affected by the politically expedient movement of satellites.
Beacon or cellular-based positioning systems - These systems have an inherent inaccuracy of many kilometres and are therefore not considered as suitable for fleet management purposes.
Data feed systems
The vehicle when it knows its position must communicate with the user of the data. Systems used include:
Satellite-based systems - The vehicle will send its position by means of a data message through a communication satellite. This is the only method that is truly nationwide and indeed worldwide.
Cellphone-based systems - The vehicle will send its position either by an SMS message or by a data signal through the cellular network and this method can be used wherever there is a cellular network available.
There are two main disadvantages to this method, each message has a cost associated with it making the running costs of fleet management potentially high. The network can also become congested leading to delays or loss of data.
Trunking radio-based systems - The vehicle will send its position by means of a radio data message sharing the resources with the voice network, a method which can be used wherever there is a trunked radio network available. The main disadvantage of this method is the potential for congestion in the trunking network leading to delays or lost data.
Dedicated tracking system radio data network - The vehicle is allocated a time slot in the network and sends its data at predetermined times or on demand using free time slots. Because the network is dedicated to vehicle tracking only, the system can be managed to remove any possibility of congestion. The costs of passing data is fixed and can be budgeted for by the user.
Fleet management interface - The last part of the fleet management system is the computer that sits on the manager's desk and facilitates the management of the fleet. This computer should be able to carry out at least the following functions:
q Realtime display of vehicle position.
q Display positions on maps at various scales.
q Display positions in latitude, longitude and street/suburb/town basis.
q Display current speed of the vehicle together with the status of various sensors on the vehicle.
q Display the temperature of refrigerated loads.
q Alert the manager to entry into or exit from defined areas (no-go or should-go).
q Alert the manager to deviations from prescribed routes.
q Alert the manager to stops longer than a set limit.
q Alert the manager to speed in excess of a set limit.
q Alert the manager to sensor input in 'not allowed' area (doors opened by side of road etc).
q Be able to set parameters that can be managed by exception.
q Record all communications from the vehicles.
q Be able to replay data from specified vehicles for a specified time in realtime and fasttime.
q Be able to generate reports with a flexible user defined structure.
Conclusion
Vehicle tracking-based fleet management is a powerful tool able to enhance the cost effective use of transport in any business. There are however many technical issues underlying effective solutions and potential users would be well advised to do their homework well.
For details contact datatrakSA on tel: (011) 444 1111 fax: (011) 444 2277 e-mail: datatrak@compuserve.com
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