Weighing in year 2004

Weighing on Slovenian highways in year 2004 was conducted with SiWIM bridge WIM systems. Duration of weighing was 14 days on five different locations. Number of heavy vehicles on overtaking lane was from 0,5% to 1,7%. Because of so small number calibration was not done on overtaking lane. Thoroughly data about locations and time of weighing are presented in lower table and are shown on picture.

Calibration on Slovenian Highway

For collecting data with WIM systems have to be calibrated.

On main roads the calibration is carried out with calibration - pre-weight vehicle. Vehicle is first weight on static scale then it drives several times over the bridge equipped with SiWIM system. Final results are calibration factors and with that procedure according to COSR 323 we can calculate also accuracy of the system.

But that was not a calibration procedure on highways. Because our highways are toll roads and distance between one exit point to another (vehicle must leave the highway and then again enter highway at the point of the root that passes specific bridge) it would be very time consuming and expensive to perform calibration as on main roads.

We decided to calibrate the system on free traffic flow. Vehicles were measured with static scales before of after they passed SiWIM system. We used from 40 to 50 different trucks to calibrate the system.

Compare between WIM data and TSC – Slovenian specifications

ESAL values measured with WIM system were compared with TSC (Slovenian Technical Road Specification) where data are collected from traffic counters. Diagram shows as differences between calculation with TSC (standards) and real measured data with SiWIM for different vehicle types.

Number of overloaded vehicles

Exceeds by the number of vehicles are pinpointing high level of overloaded vehicles except on Site 2 and
Site 4. On this section traffic was transferred from highways to local roads by the date from 2003. Percentage of overloaded vehicles on state roads was 15% in year 2003. All locations except highway section Site 3 are over the national average showing usage of state roads

Enforcement with WIM system

Existing fines policy in Slovenia is based on static controls with Police. On average there were 550 per month and 6.742 per year weight cargo vehicles in year 2003. Number of vehicles that were overloaded is 3.700. Analysis made by WIM measurements showed that, expressed as percentage this is less than 0.5% of all overloaded vehicles. It is estimated that income collected from penalties sums in 2 billions per year. Penalties are between 500.000 and 1.000.000 SIT.

WIM measurements in year 2004 are based on 5 different sites with each in average 30km long. That make in total approx. 150 km of highway which is 1/3 of national highways.  

Recommendations to cut overloads are based on presumptions:

-          main goal of penalties is not collecting money but decreasing traffic overloads

-          controls with static scales  and police should be on regular basis

-          penalties that are in use at the moment do not reflect damage made by overloads

With WIM system and appropriate legislation it would be possible to sanction violators by video capturing overloaded cargo vehicle.

This has happened despite the fact that several enforcement teams using static scales fined several thousands of overloaded trucks in 2003, which, however, corresponded to only 0,5% of all overloaded vehicles recorded with the WIM systems. Consequently, a high-speed WIM enforcement procedure is being discussed. It has been proposed to account for the real accuracy of the WIM systems and to calculate the corresponding measuring tolerances that would ensure 99, 9% confidence in the results of the overloading vehicles. Applying such tolerances to the 2003 WIM data reduced the number of ‘surely’ overloaded vehicles to only 45% of the original number. But even if all of them could be fined with amounts 10-times smaller than today, the sum of these fees would exceed 300 million Euros per year and it is approximately 30 times more than with present static control. Unfortunately, the present legislature in Slovenia does not allow yet using weigh-in-motion data for direct enforcement of the overloaded vehicles.

Furthermore:

Consequently, true life time of the pavements is much shorter then the designed one.

Graphs show a percentage of overloaded vehicles on individual site.