Loops or lasers for classifying vehicles - Texas Turnpike going for laser profilers now

The Turnpike division of TxDOT is doing something unusual in the US at least - classifying vehicles entirely with overhead equipment using volumetric laser profilers. No loops. So far the fully-overhead classification system from Raytheon is only in use on three pikes of moderate to slight traffic volumes:

- SH45 South East a new 12km (7.5 miles) long pike linking SH130 tollroad to I-35 at Creedmore on the southern fringe of the Austin metro area

- the first segments of Loop 49 an eventual 2x2 lane 51km (32 mile) pike off I-20 wrapping around the northeast Texas city of Tyler, so far open with only an isolated southern portion of 2 lanes

- Camino Colombia Toll Road TX255, a 35km (22 mile) 2 laner north of Laredo built privately but bought by TxDOT at bankruptcy, connecting I-35 to Colombia Solidarity International Bridge over the Rio Grande into Mexico

Profilers pulled out in Dallas area

TxDOT was planning the same Raytheon system on SH121 when this north Dallas pike was being concessioned to Cintra. A laser based toll tracking and classification system was ready to operate.

However when NTTA took over SH121, since renamed Sam Rayburn Tollway, they pulled out the Raytheon gear and had their regular toll systems contractor ETC put in loop-based classification to keep it consistent with their systems on the Geo Bush Turnpike and Dallas North Tollway.

TxDOT itself has a loop-based classification system on its three major Austin area tollroads Loop 1, SH45 North and SH130 segments 1 to 4. These were built prior to TxDOT's master toll systems contract with "loopless" Raytheon. On these Austin area tollroads they have the more usual axle-counting toll system, this one supplied by United Toll Systems (UTS).

UTS have a patented smart loops system embedded in the pavement at all toll points. Named IVIS for Intelligent Vehicle Identification System, it analyze the electromagnetic characteristics of the iron mass of engine, axles and underbody components of the vehicles passing over.

see http://unitedtoll.com/IVIS.html

Also in the Austin area Central Texas RMA's 183A tollroad out to the northwest corner of the metro area, vehicles are classified by axle-counting loops - these ones Idris loops installed by Telvent Caseta - from 2-axles through 6-axles.

Compatibility of two classification systems?

So how does a loop-based axle-counting classification system coexist with a profiler and a shape-based classification system?

We asked the toll operations specialist at TxDOT's Turnpike Division, Linda Sexton.

She told us that so far the combination of axle-count and shape-based classes hasn't generated major problems. It adds a bit to the complexity of toll rate charts. Others say the two approaches to classification generate a few problems in the middle range of classes such as delivery vans, but at each end - cars and tractor-trailers - there is no difference.

Sexton said any equipment in pavement has problems with maintenance when there's ground movement. TxDOT has had some of those typical problems in the Austin area, but otherwise they are happy with them.

The loop-based system on the first three tollroads goes back to a pre-Raytheon procurement and it is giving good service, Sexton says. There are no immediate plans to convert the loop-based UTS-installed system to profiling.

All new TxDOT pikes to go loopless

For the time being it is TxDOT policy to equip all new tollroads under its control with the laser profiler for vehicle classification.

Sexton says the laser profiler system performs well and a major attraction is the simplicity of maintenance.

Adjustment of equipment can usually be done on the overhead gantry without the need to close a lane.

Neither profilers nor smart loops are quite as accurate in stop and go traffic or even in slow traffic as in fast traffic. They work best with traffic moving through at steady highway speeds of 40 to 80mph (65 to 130km/hr).

Two manufacturers compete in smart loops:

- Diamond Consulting of UK are the market leaders

- IVIS from United Toll Systems, Alabama

And there are two major established laser profiler suppliers:

- Autosense from OSI LaserScan of Hawthorne CA

- SICK AG headquartered in Waldkirch in the southwest corner of Germany operating worldwide with US offices in Minneapolis

Overhead lasers, especially those from SICK are often used in conjunction with loops and not as a substitute for them. In many places they are used more to detect, delineate and track vehicles rather than to really profile or characterize the shape for vehicle classification - still done in such cases with loops.

Officials at other system integrators - TRMI, Telvent Caseta, and ETC told us they can supply and support both laser profilers and loops, saying each has strengths and weaknesses, and that the choice depends on the requirements of the customer and the locale.

An ACS guy told us the best performance can usually be gained with both lasers and loops. Redundancy, he acknowledged is a cost but there are major benefits, he said, in accuracy and consistent accuracy, when always able to look at the underside profile with smart loops and the shape from above with a laser.

Geography and weather are a consideration.

Loop advocates say heavy rain, fog and puffs of truck exhaust can blind lasers or otherwise cause their readings to go askew. Snow doesn't seem to trouble them and reportedly the lasers do fine without loop backup on 407ETR in Toronto where they get decent snows. Florida might be more problematic for lasers alone because of torrential downpours and morning mists. California, Texas and other dry states are probably the closest you get to perfect laser country.

Outside the US apparently smart loops face more skepticism than in the US, while laser profilers are used more. Major greenfields all-electronic tollroads do vehicle classification based on three or four simple shapes, well suited for detection by a video or laser profiler. On 407ETR in Toronto laser profilers are used to classify vehicles into three classes: light vehicles (5t and under), heavy single unit or straight-bodies (over 5t) and heavy multiple unit or trailered vehicles (over 5t). (They aren't actually weighing the vehicles of course but referring to a database of vehicle types by gross registered weight.)

Melbourne CityLink goes: cars, light commercial vehicles (to 4.5t gross vehicle mass with 2 axles), heavy commercial (over 4.5t). Israel's H6 and all-electronic pikes in Santiago Chile have similar vehicle classing.

In the US most vehicle classes are based on axle numbers.

Pennsylvania and Ohio Turnpikes have relied for more than 20 years on a unique weight-based classification for everything beyond cars. This goes back to early days of IBM doing toll systems.

Weight based classification

Their weight based systems are on the way out.

Ohio Turnpike recently got rid of the last of its old IBM truck scales.

The Penn Pike maintain their existing system but they don't install them at any new toll points and plan to eventually go to the common axle based classes, using loops assisted by lasers.

The IBM scales are wearing out. Also they were designed for stop-to-pay toll plaza speeds - 5 to 15mph (8 to 25km/hr) and they seriously lose accuracy when traversed at open road speeds.

The move to highspeed tolling means the day of weigh-to-class are numbered. A pity in some ways because there was always an appeal to the thought that it's the weight that damages the pavement, so weight should pay.

TOLLROADSnews 2009-10-25 ADDITIONS EDITING 2009-10-26 12:00