WEIGH-IN-FREE-FLOW

The new standard level for high-speed weigh-in-motion.

For decades, Weigh-in-Motion systems have been some of the most powerful instruments to protect roads against overloaded vehicles - trucks especially. Many companies come to the market with different technologies for low-speed and even high-speed measurement with the accuracy floating from 20 per cent to the highest possible level of ±5 per cent. The systems enable many applications for statistical purposes, such as pre-selection with an active assistance of the police, and finally, some countries have even implemented legislation for direct enforcement. That all sounds great if …! If the systems could make valid measurements across the whole width of the roadway.

The limitations of current Weigh-in-Motion units

Despite their indisputable advantages, the current most widespread sensors used for dynamic weight measurement of vehicles in motion suffer from various limitations. The first examples of constraints consist of manoeuvres during dynamic weighing. In most cases, the sensors are arranged in two or more rows which allows repeating the measurements for higher accuracy. However, the sensors require the vehicle to move straight. As soon as the vehicle moves in a skewed direction, it is not possible to perform accurate measurements. Another limitation is the inaccuracy at the edges of the sensors. This limitation reflects the design and location of the sensor itself. The sensors are positioned horizontally in each lane. However, they are not equally distributed in the full width of the lane. While the measurement is the most accurate at the centre of the track, it is not sufficient on the ends of sensors. If the vehicle moves between two lanes or at a lane side, the measurement is not reliable. This, of course, creates an opportunity for dishonest drivers to avoid weighing and subsequent fines.

Weigh-in-Motion and the reduction of maintenance and repair costs with Toll-per-Tonne

With the aim to capture and to record the axle and gross weights of vehicles the Weigh-In-Motion units represent the most up to date solutions for traffic flow monitoring and regulation on the busiest communications. This automated system helps to detect the load violations, to save the human resources as well as the time needed for resolution, and of course, decrease the funds spent on the manual procedure and the road maintenance costs. One of its biggest contributions is the opportunity to create the system of paying tolls per weight. With the concept of Toll-per-Tonne, each vehicle would pay exactly per each tonne of its load, which would make current conditions much fairer, more transparent, and eventually, it might lead to the reduction of overloaded trucks.

Weigh-in-Motion and the reduction of maintenance and repair costs with Toll-per-Tonne

As the volume of transportation has been extending in recent years, all types of roads have been dealing with the never-ending influx of vehicles that tend to violate certain rules for the sake of saving resources. One of the most severe violations is exceeding the load's weight limit that leads to road impairment causing additional burdens for maintenance and, therefore, a constant increase in repair costs. From a huge part, the expenditures are covered by toll fees.

With the aim to assess and to record the axle and gross weight of vehicles, the Weigh-In-Motion units represent the most up to date solutions for traffic flow monitoring and regulation on the busiest roads. This automated system helps to detect the load violations, to save human resources as well as the time needed for resolution, and of course, decrease the funds spent on the manual procedure and the road maintenance costs. One of its biggest contributions is the opportunity to create the system of paying tolls per weight. With the concept of Toll-per-Tonne, each vehicle would pay exactly per each tonne of its load, which would make current conditions much fairer, more transparent, and eventually, it might lead to the reduction of overloaded trucks. But these visions have significant requirements – to be able to make the measurements in real free-flow of passing vehicles, and to increase the accuracy into A3 level according to WIM standards, which means ± 3 per cent of gross vehicle weight.

The requirements and possibilities of Toll-per-Tonne classification

Even though the most widespread Weigh-in-Motion systems on the market provide measurements with the emphasis on the highest accuracy possible, the tolerance of measurement in the most precise units is about 5 per cent. In order to prevent potential future court disputes, that would be based on inaccurate weigh assessment, and therefore unfair charge for the toll, the possible implementation of Toll-per-Tonne to the traffic would require settling specific classifications including various degrees of tolerance. The exact procedure of classification assessment is still under discussion, yet the need for resolution remains apparent.

The future challenges of Weigh-in-Motion development

To improve toll collection and establish the Toll-per-Tonne solutions as the major way of keeping the roads in the appropriate state with adequate resources, the Weigh-in-Motion units will have to resolve current imperfections. The main emphasis will have to be put on improving the accuracy of measurement. Five percent remains to be too high of a number to keep the toll recollection fair. For years, a number of countries have the A3 level - the high-speed weighing accuracy of ± 3 per cent - incorporated into their outlook plans. Also, the sensors need to cover the whole space between the lanes so that there is no option to violate the system. The last area that requires improvements is the issue of a lane coverage adjustment. The units should be able to assess the weight comparably no matter the vehicle’s location in the lane. Once all these deficiencies are overcome, there won’t be anything standing in the way to establish an efficient, time and money saving, and fair system of toll collection.

But it is not just about the accuracy of those ±+/- 3 per cent, there are far more criteria and parameters the modern WIM system must meet.

Maybe we would not even have to call it WEIGH-IN-MOTION but WEIGH-IN-FREE-FLOW.

Links

Weigh-in-motion association ISWIM - http://www.is-wim.org/

Traffic Technology WIM edition - http://viewer.zmags.com/publication/384220a2#/384220a2/1

Free-flow fibre optic WIM sensor OptiWIM - http://www.optiwim.com/

Wikipedia - https://en.wikipedia.org/wiki/Weigh_in_motion