Idris loops going deeper - vehicle classification for open road tolling CORRECTION

Idris loops, now a mainstay of highspeed automatic vehicle classification on US tollroads can now be placed deeper in the pavement, the licensing company says. At the previously specified depth of 20mm (under an inch) this has meant that pavement milling operations, undertaken every eight or ten years, are likely to chew up the loops.

Diamond Consulting Services Ltd which developed and licenses the Idris loops say that improvements they have made to the sensitivity of their systems allow them to certify them as accurate to >95% accuracy (their established standard) down to 50mm (2 inches) depth in pavement.

This should allow milling operations without endangering the loops.

Milling is really only an issue in asphalt and most installations are in sections of special concrete. Concrete is not regularly milled.

Idris inductive loops like other inductive electromagnetic loops generate an electrical current signal when the iron mass of vehicles travels over them. 'Smart loops' so-called consist of methodologies for arranging the shape and placement of loops and application highly researched and often patented algorithms to the signals - often called digital signal processing - to enable axles to be counted and hitches detected.

Idris' major competitor in the US is United Toll Systems (UTS) which has an electro-magnetic in-pavement sensor system called IVIS (Intelligent Vehicle Identification System). IVIS is placed at a depth of 32mm (1.25 inches) and the company reports accuracies of over 99.9% (though we haven't established that the comparisons are tests on an equal basis.)

As all-electronic toll collection spreads the companies see an increasing demand for vehicle classification systems that could be placed in a stretch of pavement made of asphalt - the most common pavement.

In any case the slightly deep placement helps protect the sensor arrays and assure a longer life.

Vehicle classification is needed to assign the correct toll rate where toll rates vary by the size of vehicle, or as is most common in the US by number of axles. Piezo and fiber optic sensors are other less favored new technologies for axle counting. But in single lane applications including in electronic toll lanes the mainstay is still the long established but refined electro-mechanical treadle, that many toll people still swear by (and a few swear at) in combination witha light curtain to establish vehicle separation.

Overhead vehicle profilers using lasers, infra-red or optical imaging and analysis to get a measure on the size and volume of passing vehicles can assess the bulk of vehicles and are often preferred where there is no axle count tradition of classification as in completely new tollroads.

On the two electromagnetic classification systems most commonly used in the US

see http://www.idris-technology.co.uk

and http://www.unitedtoll.com/ivis.html

TOLLROADSnews 2008-04-11

CORRECTION: Idris is not yet being recommended for tolling placed at depth, says Teri England of Diamond Consulting, the developer and licensee, because it doesn't get the accuracies usually demanded at 50mm (2 inches) yet. The company is working toward that goal. Deep placement is now only recommended for traffic data collection. see http://www.tollroadsnews.com/node/3494

TOLLROADSnews 2008-04-16