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Weigh-In-Motion
Learning from Experience
David Cornu, Kistler Instrumente AGWinterthur, Switzerland
Special Print from Traffic Technology International, August/September 2008
Special Print920-367e-06.13
TECHNOLOGYPROFILE
Learning from experience
orming part of the program to reduce the overloading of heavy trucks, a network of WIM systems
has been deployed by the Dutch Ministry of Transport on a number of highways in the western part of the Netherlands. The first sites were installed in 2001 and another two completely new WIM systems have recently become operational. In total, eight WIM sites are up and running, all of which are connected to a central system. A great deal of practical experience has been gained since the program started, which has helped generate a realistic picture of the possibilities of WIM systems in general.
Three separate organizations are using the WIM systems for different needs. The National Traffic Police Agency employs them as a preselection tool to increase the efficiency of their static roadside overload controls. The Transport Inspectorate uses the recorded images of the overloaded vehicles for company profiling and overload prevention, while the DVS (Centre for Transport and Navigation) utilizes pavement load data for pavement design and road maintenance, as well as for statistics and traffic analysis.
THE wim-NL sYsTEmA standard WIM-NL system covers all lanes of the highway. Where trucks are permitted, lanes are instrumented with two induction
owner of the vehicle. If a certain company has been recorded several times, preventive actions are taken against that company.
The system is used by traffic police in the Netherlands as a preselection tool for the static weight controls. The static weighing sites are situated 2-4km downstream and are connected via the WIM-NL network with the corresponding WIM site. For the preselection process, a WIM monitor is used. For each passing vehicle, the display shows the image, license plate detail, classification and weighing data. Preselected vehicles are taken through the static weighing process to determine the actual violation, which is legally required by Dutch regulations, because only static measurements can be used for prosecution.
dECisiON-makiNG prOCEssRonald Henny was the former head of Pavement Loading and Winter Maintenance at the Road and Hydraulic Engineering Institute (now known as DVS – Centre for Transport and Navigation) of the Dutch
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loops, two rows of Lineas quartz WIM sensors provided by Kistler, and a license plate recognition camera. The remaining lanes are equipped with loops and cameras to record the trucks that illegally pass over the lanes. All vehicles driving through the WIM site (developed and tailored to the customer’s specific needs by Technolution and TEC Traffic Systems in the Netherlands) are measured with relevant truck information stored, such as vehicle classification, speed, axle weight, etc. The legal weight limits are determined based on the results of the classification – if a violation is detected, the measurement record will be combined with an image of the license plate and also an overview picture of the side of the truck.
The measurement data of all trucks passing by the system is recorded 24 hours a day, seven days a week, and stored in a central database, to which many organizations are given access in order to use the data for their own individual purposes.
The Transport Inspectorate uses the images of the overloaded vehicles to trace the
TECHNOLOGYPROFILEby David Cornu, Kistler Instrumente AG, Switzerland
TRAFFIC TECHNOLOGY INTERNATIONAL AUGUST/SEPTEMBER 2008 101
The WIM-NL system with Lineas quartz WIM sensors, as installed by TEC Traffic Systems
Kistler’s installed Lineas quartz sensor
A network of WIM systems used on highways in the Netherlands are providing the perfect platform for advancing technologies to prevent truck overloading, while generating valuable data for a whole host of agencies
Load bearing (can be ground)
Elastic material (foam)
Quartz (sensing element)
Special alloy profile
Sand-epoxy grouting
TECHNOLOGYPROFILE
Ministry of Transport. Over the past decade, he has been a key figure in the introduction, development and use of WIM systems in the Netherlands. In addition to these national projects, he was also involved in several European projects, such as COST 323, WAVE, TOP-TRIAL and REMOVE.
Kistler’s quartz WIM sensors were selected as standard technology for the WIM-NL network, mainly as a result of promising results achieved on several European projects, but also due to the great potential in terms of performance and accuracy. The use of weighing plates on the Dutch highway network led to certain installation problems, while alternative piezoelectric strip sensors were not able to meet the accuracy and reliability requirements. Subsequently, the Lineas sensor was selected.
GrEaTEr durabiLiTY One particular strong point of Lineas is the high quality of the sensor – a consequence of unique measuring technology, design, and fabrication process – which results in high accuracy and long-term stability. Durability, however, was initially a weak point. Measurements showed that the axle loads as well as the frequency (number of heavy vehicles/axles) were extremely high on the Dutch WIM sites, which resulted in an increased wear and tear of the sensors. However, after a change in the design and production process, designers were able to notably improve durability.
The installation of any WIM sensor is a critical process and the specific ZOAB pavement (drain asphalt) on the Dutch highways required even more careful
treatment. Due to the rainy climate in combination with the ZOAB pavement (which contains water over longer periods after rainfall), and the severe restrictions for road closures (allowed only during certain periods at night), the installation posed several challenges.
CaLCuLaTEd TO pErFOrmHenny is convinced that Lineas quartz sensors can measure an actual (dynamic) axle load very accurately with an error rate below 3%. The problem, however, is always the reference. A statically weighed axle is generally used as reference, but a WIM measurement is dynamic, so the axle load of the vehicle is not constant. As a result of this, the calculated accuracy will also depend on pavement quality and vehicle
suspension performance. Over the past few years, accuracy levels of ±10% have been achieved for 95% of the axle load measurements. A better accuracy can only be achieved through the use of multiple-sensor systems in combination with dynamic calibration and intelligent processing.
In Henny’s opinion, developments for future applications will include the direct enforcement of overloading, which is a technical as well as a juridical challenge, and tolling based on weight will also advance.
To assess the technical possibilities to build a WIM system that can be used in the future for the direct (automatic) enforcement of overloaded heavy vehicles, a large project (called WIM-Hand) was started in 2000. Here, a multiple-sensor WIM system with 16 rows of Lineas sensors was designed and tested together with an instrumented vehicle for the dynamic calibration of each individual sensor within a total array of 32 wheel-load sensors. To prove the required high accuracy and reliability of the system, extensive tests were performed. These tests involved the weighing of more than 1,000 trucks, both dynamic and static. However, the results of the project still have to be officially published by the DVS. n
To find out more, please contact Kistler Instrumente AG by telephoning +41 52 224 11 11, or emailing [email protected]. Alternatively, you can log on to www.kistler.com
Vehicle data on the WIM system monitor, by Technolution. Both license plate and vehicle are shown
The Lineas sensor was selected for the Netherlands WIM project as it met all the criteria needed in terms of accuracy and reliability
TRAFFIC TECHNOLOGY INTERNATIONAL AUGUST/SEPTEMBER 2008102
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