But an interesting case happened at the end of last year in Slovenia, where police regularly use SiWIM bridge weigh-in-motion systems for preselection purposes. A driver of a 59-ton 5-axle articulated lorry without an exceptional transport permit tried to avoid detection by weigh-in-motion systems by driving towards his destination on the emergency lane of the motorway.

Despite not being calibrated for weighing vehicles on the emergency lane, the SiWIM system was able to detect the vehicle’s signal and also measure its gross weight with a 6 % percent accuracy. The B-WIM supervisor from the traffic information center forwarded the information on the vehicle to the police, who prevented the driver from continuing his journey. Since the B-WIM systems use the whole bridge as a weighing platform, their weighing sensors have no problems with weighing vehicles, which want to avoid detection by driving on the emergency lane.

These kinds of severely overweight vehicles do not only cause extreme road degradation, they are also dangerous from traffic safety point of view, which is why the coordination between traffic information center and the police is so important. The described real-life example showed the practicality of bridge weigh-in-motion systems when it comes to unusual driving patterns of drivers, who would like to avoid detection.

Increasingly, they are being incorporated into the traffic control centers, where they serve as an important part of comprehensive monitoring of road infrastructure.

Bridge weigh-in-motion systems (B-WIM) are a special type of weigh-in-motion systems, that are installed under a bridge, which is used as a weighing platform for the passing vehicles, measuring their gross weight and axle loads.

The set of data gathered by B-WIM systems is extremely valuable to the owners of the road network and the authorities as countries have strict legislation in place to govern the maximum permissible gross weight and axle loads of heavy goods vehicles. If overloaded, these vehicles cause the largest amount of damage to the pavement, so it is paramount to identify and eliminate them from the traffic as soon as possible.

In 2016, the Motorway Company in the Republic of Slovenia (DARS), which operates the motorway network of Slovenia, was the first in the world to incorporate B-WIM systems into its traffic control centers. Ulrich Zorin, director of Motorway Management at DARS: “We decided to implement the system because of safety and better traffic flow. In our main traffic management control center, we have a 24-hour traffic control team, that is closely linked to the police and the weighing teams. Concentration of information in one place ensures the flow of the main traffic artery through Slovenia.”

They currently use between five and ten SiWIM B-WIM systems, some are placed on permanent locations, while others are moved between different road sections. A traffic technician, who is present in the traffic information center, is monitoring systems via on-line application – when an automatic warning alerts the technician of an overloaded vehicle, the procedure of eliminating it from traffic can be initiated. Since the motorways are covered by cameras, the location of the overloaded vehicle is surveilled and relayed to the motorway police units, who can then eliminate it from the traffic. This same procedure is also used to monitor exceptional transports and check if the actual weight of the vehicle, axle loads and its speed matches the data on the permit.

The importance of continuous monitoring of traffic with weigh-in-motion systems was especially evident during the lockdown in the early months of the COVID-19 epidemics. With substantially fewer heavy goods vehicles on the roads, police presence was also reduced, which resulted in a sharp increase in the number of overloaded lorries and serious infringements. This was detected by DARS’s B-WIM systems and as a result police increased its presence on the roads. When weight controls were again implemented, it took over two months for the number of overloaded lorries to return to a lower pre-lockdown level.

By integrating B-WIM systems into traffic information centers, the owners of the infrastructure get valuable information on vehicles that have the biggest impact on road quality. In the EU, the monitoring of overloaded vehicles has become obligatory for the member states since May 2021. With the growth of road freight transportation projected all across the world, more countries will follow suit, as only systematic monitoring will enable owners of the infrastructure to reliably identify the problematic vehicles and help the authorities in preventing damage to the roads.

The aim of the operation is to upgrade our digital presence in the German and French speaking markets. The investment is co-financed by the Republic of Slovenia and the European Regional Development Fund.

Funding received: 30.000,00 EUR.

More information about cohesion policy in Slovenia: www.eu-skladi.si

SiWIM has been used all over the world for measuring the response of bridges under traffic load for many years. Sensors are installed on the bottom side of a bridge deck to gather relevant information and find hidden reserves, which can be considered in the reliability analysis of the structure.

Given the extreme weather phenomena and rising temperatures linked to global warming already present a considerable factor in infrastructure maintenance, using the data collected with the B-WIM system will become an even more critical part of bridge reliability assessment.

Besides the imminent threat that strong winds, hurricanes and extreme daily fluctuation of temperature pose to a damaged structure of a bridge, the long-term effects of changing climate will cause accelerated degradation of a material due to carbon induced corrosion, increased precipitation and humidity.

The gravity of the problem of deteriorating state of bridges in the era of global warming was illustrated in a paper written at Colorado State University, where authors speculated that 1 in 4 steel bridges in the USA is in danger of collapsing in the next 20 years (ref).
However, extreme weather patterns do not only affect the structures. They also have a significant effect on the equipment used for bridge assessments.

Cestel’s experience in setting up their system in different weather conditions, from tropical regions with extreme rainfall to subarctic climate in Finland, has shown many challenges in installing and operating a complex array of sensors and computers in such an environment.

Building on this experience, the emphasis behind the design principle of the new SiWIM generation was put on high reliability and remote access to the system without the reduced need for on-site intervention for system management.

Beside temperature compensation, which has for years been an essential part of SiWIM due to the effects of daily temperature fluctuations on the quality of results, sensors and computers can now also be reset remotely.

A failure of a bridge in a remote area can have especially detrimental consequences on the local population, as the damaged transportation network causes a cascading effect, where emergency services are unable to access the area.

With the heat waves and extremely low temperatures becoming more and more frequent, attention was also focused on increasing the temperature interval on which 4th SiWIM generation can operate.

As the infrastructure around the world is aging rapidly, the effects of global warming will put additional stress on the already deteriorated structures.
Reliable and autonomous bridge assessment will thus become an integral part of infrastructure maintenance.

Kickoff meeting with the client

The first step before the commencement of measurements is a kickoff meeting with the client.

The following topics need to be addressed:

• What is the purpose of the measurement (preselection, traffic analysis etc.)?
• A broad list of bridges on a given road section needs to be prepared by the client.
• Are there any special environmental factors concerning the proposed locations (is there a possibility of electrical supply from the grid, what is the mobile network coverage, how accessible are the bridges and the area under the bridges etc.)?

An exact timeline has to be agreed on.

After the general topics have been discussed, the bridge inspection can be done.

Bridge inspection

Proposed bridges are then inspected by Cestel’s technicians and engineers together with the representatives from the client.

They check the structure of the bridge, the state of the road surface, access under the bridge, they take the relevant measurements etc. Bridges are ranked according to their suitability and expected measurement accuracy.

After the inspection is completed, the client is given an Inspection report on the basis of which a decision is made on the bridges that will be used in the measurements.

Configuration setup

Using CAD software, Cestel’s technicians draw the configuration setup for each bridge where the position of sensors, cables and cabinets is precisely determined.

The configuration drawing is used by the field team during the installation phase.

Installation

Installation of the sensors and cabinets takes about 8 hours. The first installation is usually made by Cestel’s field technicians, but the long-term users of the SiWIM system are generally trained by Cestel for an independent use of the system.

It is discussed with the client before the start of installation if any special equipment, such us a bucket truck, is needed during the setup of the system.

Calibration

The system is calibrated using a truck with known weight supplied by a local subcontractor. The duration of the calibration process depends mostly on the distance that the calibration vehicle needs to travel before it can make a U-turn.

After the calibration is completed, an accuracy assessment of the installed system can be made. It is included in the Installation and calibration report.

Measurements

During the measurement, the system is supervised by Cestel’s technical support. The length of the measurement is determined in discussion with the client at the start of the project.

Measurements last anywhere between two weeks, which is long enough for a traffic analysis report, and a couple of years, such permanent installations are usually implemented when SiWIM is used to its fullest capacity – as a tool for preselection, traffic reports and bridge assessments.

Deinstallation

Deinstallation of the system is done very quickly – usually it takes less than 3 hours. All of the holes that were drilled to attach the sensors are filled with a concrete paste. After the deinstallation is completed, a report on the process is prepared.

Data processing, analysis and report

The gathered data is then analyzed by the traffic experts in Cestel’s analyses department. A report is prepared in line with the client’s topics of interest and is also accompanied by recommendations.

The owner of the road network, the Public enterprise roads of Serbia, was thus given a quick overview of the real traffic loads across the country, which is an important information for future road planning, maintenance and law enforcement authorities for whom the statistics on overloaded lorries is of crucial importance.

Due to the short time frame of the project, five SiWIM MkIV B-WIM systems were used simultaneously. They were installed by a two two-men team of Cestel’s field technicians, which on average took eight hours to install a B-WIM system. When a 14-day measurement on a particular bridge was finished, the system was de-installed, loaded into a van and transferred to a new location in the same day. Since the data gathered by SiWIM is accessible on-line, a traffic expert started preparing a traffic analysis report immediately after a measurement was completed.

The project in Serbia showcased practicality and cost-effectiveness of bridge weigh-in-motion systems when it comes to quickly mapping distribution of the traffic loading over large parts of the road network. This is especially important for countries, which are just beginning to invest in WIM technology, and can thus get a fast overview of hotspots where overloaded lorries have the largest impact on the road surface.

But these colossal structures are exceptional in this regard, since the structural health monitoring systems are way too expensive to be used on tens of thousands of other bridges, which are used by people every day.

Portable bridge weigh-in-motion (B-WIM) systems can fill in this information black hole which is currently hovering over arguably the most important part of a country’s infrastructure. They give structural engineers missing information on the true behavior of a bridge under traffic loading with the help of the true influence line, real load distribution and the information on dynamic amplification factor.

Such analyses, which can be done on the basis of short-term B-WIM measurements, have many practical applications for the owner of the structure. They can be used to either post a bridge for restrictive loads or reduce the existing posting limitations, which has enormous benefits for the population and economy in general. The data can also be used to adjust the inspection schedule of the structure and plan the future maintenance works. Real-life experience shows that most of the bridges are overdimensioned and B-WIM based bridge assessment thus often results in an increase in the lifespan of the bridge or serves as the first step in a more comprehensive monitoring of the structure.

While the infrastructure is rapidly aging, bridge owners have virtually no information on the state of bridges. Portable B-WIM technology offers a practical and economical solution to this information void and gives infrastructure owners the possibility of a methodical structural overview of bridges.

The most severe infractions of gross weight and axle load restrictions are usually found near certain sources of heavy goods vehicles (HGV), such as quarries, sawmills and construction sites. Portability of the SiWIM B-WIM system enables its users to install and move the system between these locations, accurately measure gross vehicle weight and axle loads of heavy vehicles and, with the help of an advanced vehicle classification system, determine the origin of overweight HGVs.

In Slovenia, the Ministry of Transportation devised a methodology for determining the division of costs of excessive traffic burden of cargo vehicles. In line with this methodology, Cestel’s traffic experts have been using data gathered by SiWIM to convert axle loads into a monetary assessment of damage. They use ESAL values to calculate the impact of overweight axles on the pavement and determine the proportional cost of damage caused by overweight vehicles from a particular quarry, construction site or other similar locations. Since 2012, between 35 and 85 such measurements have been performed each year in Slovenia.

This system is similar to weight-based tolling and is especially important for small municipalities with low budgets, as they can use it to claim damages and thus finance reconstruction of infrastructure. Road damage is thus paid for by legal entities which own the overweight vehicles and, at the same time, monitoring potentially problematic sources of overweight traffic also encourages adherence to weight and axle load regulations.