Vehicle Classification - The Road To Fair Tolling
Toll roads, bridges and tunnels, which motorists must pay a fee to use
, bypass busy areas to ease traffic congestion, generate funds for road upkeep and repair, and often provide substantial revenues for governments and private companies. Highly beneficial in the main, toll roads present a unique set of problems associated with the collection of the correct tolls from users.
Toll collection techniques
Toll collection techniques fall into two categories, free flowing where traffic flow is not affected and non-free flowing where vehicles stop or slow to pay the toll. The choice of toll collection technology will have a significant impact on the efficiency of the toll collection process.
Efficient toll collection
Toll collection efficiency compares the amount of toll revenue collected to the cost of collection. The toll road operator wants to ensure that the maximum revenue is collected. Their customers, the motorists, want free flowing traffic and no delays. For the operator these sometimes-conflicting needs have been resolved by favouring toll collection over traffic flow. This is particularly true with non-free flowing systems.
As traffic density increases the balance changes. Toll collection lanes and booths may struggle to handle peak volumes resulting in reduced revenues and frustrated customers. Automating the toll collection process, so it becomes free flowing, can often be the most cost effective solution. However, free flowing toll collection requires systems that will perform checks an operator finds easy but that present significant technological challenges.
Toll charges based on vehicle type
Most toll charges vary according to vehicle type; the bigger it is the more the driver gets charged. Visually checking the vehicle an operator knows which category a vehicle falls into, whether it has a trailer and which weight band it is likely to fall into. Two vehicles arriving together can be easily distinguished from a single vehicle with a trailer, and a car with a roof box will not be mistaken for a commercial vehicle.
Automated toll collection depends upon systems that accurately and reliably perform these checks and classifications at high speed. They must perform at night, in poor weather conditions, and must work together with other systems that identify the vehicle so that the correct toll can be collected from the vehicle operator.
Laser-based classification systems
Advances in laser technology and reliability have led to systems that use lasers to generate a 3-dimensional model of each vehicle entering the tolling area. Three lasers mounted as a single unit on a pole at the roadside scan a vehicle as it enters the tolling area at speeds up to 40km/hr. Mounted ten metres from the toll barrier the system has enough time to scan and classify the vehicle before it arrives at the barrier.
Classifies over 99% of vehicles correctly
Smart computer systems enable the system to filter out inaccuracies caused by vehicles varying their speed and even reversing in the classification area. Vehicle separation can be as little as 0.2 metres and the system will determine the vehicle's height, width and number of axles. It is possible to set height, width and axle limits to prevent vehicles large or heavy vehicles accessing the toll way.
Capable of working with cars and trucks from one to thirty metres long the system can even determine the vehicle's classification before the whole vehicle has passed by its lasers. For road operators, the systems' freestanding construction means no in-road loops or sensors, reducing installation costs and disruption.
Laser systems can achieve a classification accuracy of better than 99% in all weather conditions and classify more than one million vehicles daily in a free flowing traffic situation.
ANPR systems
To maximise the benefits of automatic vehicle classification during toll road charging, a system of vehicle recognition is required. Reading vehicle number plates is of course the accepted method. Again, such systems must be reliable, able to differentiate number plates in poor weather conditions and with very high levels of accuracy. Free flowing traffic systems will want systems that can work across multiple lanes and deal with the problems of tailgaters and toll evaders.
Good ANPR systems use high-resolution cameras, triggered by a special laser detection sensor (LIDAR), to capture images of passing vehicles' number plates. They interpret these images using computer algorithms and optical character recognition (OCR) techniques. ANPR systems like these reliably identify national and international license plates on multiple parallel lanes, irrespective of the speed or the position of vehicles. Even during poor weather, strong sunlight or snow, they read most license plates correctly.
Good ANPR systems operate with only one gantry per location and require no roadside installations, meaning they can be constructed in a short time and without significantly disturbing traffic flow. Having classified the vehicle using the 3D laser-dimensioning device, and captured its number plate and an image of the driver, the toll road operator now has the means of charging for the road's use without necessarily stopping the vehicle to collect payment. ANPR systems will work with on board dedicated short-range communication (DSRC) units, which confirm that the vehicle details are valid
A complete freeflow toll collection system
Combining systems such as these gives the toll road operator a means of introducing a freeflow toll collection system that will enable them to meet the demands of their customers: Free flowing traffic that is not delayed by the toll collection, thereby loosing one of the key benefits of the toll system.
by: Malcolm Smith
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