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| The American Way - Inductive Loops for Road User Charging. Article prepared for Diamond Consulting Services Ltd.
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4/5/2005 |
| Uncomfortable decisions have to be made - and quickly. The continuing explosion in car ownership throughout the world and the consequent strain on national road networks increasingly points to the need for improved systems of demand management. In the United States, discussions are already under way at the political level to allow the introduction of road pricing systems on freeways. In Europe, there is a resigned acceptance of the fact that universal road user charging is almost certain to be introduced some time after 2012 and work is well underway in the search for a fully interoperable system of payment. In China, most if not all, highway construction programmes are geared towards the principle that the user pays. But difficult though the political decisions relating to the introduction of systems of demand management may be, there is another, more pragmatic hurdle that will need to be crossed.
In the United States, as in other parts of the globe, the vast majority of tolling facilities still rely on manual and automatic stop-go systems of payment that on busy routes will often result in unacceptable delays to traffic. In the years ahead, it is expected that the problems associated with the need for tolling plazas will be resolved through the deployment of GNSS (Global Navigation Satellite Systems) technology allowing for tolling fees to be collected remotely. In the meantime there are a range of other solutions for dealing with the conflicting demands for free flowing traffic and the imposition of some system of demand management that are only now being seriously considered. High on the list is inductive loop technology.
The problem, as is so often the case in any commercial undertaking, is one of cost. The infrastructure necessary to produce an efficient tolling operation is hugely expensive and, once built, is expected to produce a return on investment that will satisfy the share holders. This applies no less to the technology involved as to the bricks and mortar of the facility and will be reflected in the long-term strategy of the individual tolling service providers.
At an increasing number of plazas in the United States, a policy of flexibility designed to meet the needs of the road user has manifested itself in the provision of both automatic and ORT (Open Road Tolling) lanes capable of dealing with a range of vehicle classifications. In a handful of locations, the authorities have also begun to look at the question of pre-classification tolling as a means of further improving the throughput of traffic. One such example is in Florida where the FDOT is currently in the process of evaluating the principles of pre-class tolling for its 750 toll lanes. The RFI (Request For Information) document was issued in October last year and the result is expected to be made public shortly. One of the stumbling blocks is the relative difficulty of installing classification arrays in the congested environment of the pre-payment area. As a result, the FDOT has indicated that it will only consider in-pavement detection and classification systems such as inductive loops.
"The technology required to operate a pre-class system is exactly the same as that needed in a post-class array," explained Bob Lees, Managing Partner of the Buckinghamshire-based Diamond Consulting Services. "The problem is that above-ground equipment is always vulnerable to accidental damage from passing traffic and has to be protected by expensive barriers. This is especially true of the classification arrays which need to be at least 25 metres in front of the payment booth so as to accommodate large lorries."
Elsewhere in the US, other tolling authorities continue to concentrate their efforts on the less controversial and better established principles of post-class tolling. But as with Florida, many have opted for in-pavement systems, particularly inductive loops, to provide the high quality of service that is now universally expected.
And the reasons are not difficult to find. While there are a number of technologies supporting in-pavement systems, including treadles and piezos, the mechanical nature of the devices makes them prone to break-down over time (typically, one million overpasses) and the gradual deterioration of performance in the period leading up to complete break-down. By contrast, loops deploy no moving parts and rely on a magnetic field created by the presence of an overhead vehicle. The signals generated by this magnetic field pass to a CPU within the lane controller. A further, significant advantage of these in-pavement loops is that they are able to perform under all weather conditions without loss of performance.
Pre-eminent in this field of endeavour is Diamond Consulting Services (DCS), a British R&D company based a few miles outside London. Over the past eight or nine years, DCS has succeeded in developing its Idris® loop technology product into a precision instrument producing accuracy levels in the order of 99.8% in the detection, classification and identification of individual vehicles.
Behind the astonishing reductions in the error rates typically experienced in the early part of the last decade, is the development of a series of advanced and highly complex algorithms that for the first time provided transportation engineers with precise data on the classification of vehicles passing overhead. A few years later, at about the turn of the century, AVI (Automatic Vehicle Identification) was added to the range of functions able to be performed by the new system. Error rates which had previously stood at around 1:100 now tumbled to an impressive 1:10,000.
Generated in real-time, the data is made instantly available to the CPU in the lane controller for cross matching with the vehicle's OBU (On-Board Unit). At this stage, the system deducts the appropriate fee or triggers the enforcement cameras.
For the first time, tolling operators from Chicago to Miami were able to offer genuine open road tolling, facilitated by the ability to lay the loops end-to-end across the width of an entire carriageway. Amongst the first to take advantage of this opportunity were the Delaware DOT and the North Texas Tollway Authority (NTTA) who each saw the huge advantages in terms of improved throughput of traffic and customer satisfaction.
In 1996, the Delaware DOT awarded the contract for the creation of an Open Road Tolling facility at Biddles Corner on SR1, to Peek Traffic (now part of the Quixote Corporation). Four express ETC running lanes and their associated hard shoulders were created in the centre of the carriageway with the remainder of the outer lanes being retained as a manual/automatic operation.
"Peek got the contract because DelDOT were satisfied that we were able to deliver a high quality product that met all their requirements," said Vance Williams, Director of Product Support for Data, Detection and Tolling at Peek Traffic. "An important element in the DOT's decision was the knowledge that they would be getting Idris and they wanted the accuracy that Idris could provide."
Nearly five years later, in April 2004, the Delaware DOT demonstrated their satisfaction with loop technology by again approached Peek Traffic and asked them to design and build a new express tolling facility on the same SR1 highway at Dover. As with the development at Biddles Corner, the Dover plaza had to cope with a mix of commercial, multi-axle trucks and private vehicles using the four express lanes.
"The SR1 is a busy road," said Williams. "We could not have managed to handle the volume of traffic without serious congestion problems had we not designed the plaza with an ORT facility. The attraction of the Idris loops is that they are highly robust as well as being accurate to an extent that can't be matched by treadle or light curtain technology."
By 1999, in Dallas, Texas, the North Texas Tolling Authority (NTTA) had grown increasingly dissatisfied with the level of performance of its tolling facilities on the 47 mile Dallas North Tollway and the President George Bush Turnpike. High maintenance costs combined with lane closures, mis-classifications and phantom transactions arising out of the use of conventional treadle and light curtain technologies had persuaded them to look for a more reliable alternative. The contract for the upgrade was won by ETCC (Electronic Tolling Collection Corporation), and Idris loops were used to replace the multiple, and ultimately inefficient, technologies that had preceded them.
The reputation of the loops has now spread rapidly. On the massively busy New Jersey Turnpike, the Idris system controls the Exit 1 plaza and allows free flowing traffic at a bottleneck which used to see 13 mile queues at peak holiday periods. At the Pleasantville Toll Plaza on the nearby Atlantic City Expressway, a similar operation has been carried out on the directions of the South Jersey Transportation Authority. On the 47 mile E470 route, south of Denver, Colorado, problematic treadles and light curtains unable to cope with the severe weather patterns, have been replaced by inductive loops.
And so it goes on.
Whether dealing with truck express lanes in Chicago, Illinois or the mixed traffic in Miami and the rest of Florida, US tolling authorities have signalled that they are no longer prepared to put up with the loss of revenue that comes from inaccurate ETC systems or those that compel the closing of fee-generating lanes for the purposes of routine maintenance. Based on sound economic arguments, they have opted for change and are they are turning instead to systems that can guarantee accurate, year-round performance under all weather conditions. In almost every case, this has meant a switch to Idris.
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