Chapter 4: Unique Data Applications
Real-time WIM data are used most often for preselection during mobile enforcement operations and, to a lesser extent, for scheduling the best days, times, and locations for optimum enforcement. The use of these data to support planning, historical trend analysis, policy and pricing decisions, design, structure analysis, permitting, etc., was observed to be more limited. Data quality was reported to be largely sufficient for each of the various applications (i.e., preselection, planning). The most common shortcoming noted was geographic coverage.
Data exchange and sharing within the countries visited vary, and limited data are exchanged and shared with the European Union under special efforts such as the European Control Route (ECR), an international review panel dedicated to improving commercial motor vehicle size and weight enforcement. Implementation of a European WIM database, as envisioned in the COST 323 and WAVE Projects, has not been fully realized.
CMV Size and Weight Data Collection and Use
Over the last 3 years and with the advent of the SiWIM system, a network of 30 data collection sites has been established to cover all major routes of the state road network in Slovenia with portable bridge WIM systems. Five SiWIM systems are used to collect data at these sites twice per year for 1 week (the same approach is used Sweden and Croatia). This network coverage has allowed Slovenia to better monitor traffic and apply this knowledge to improve roadway planning and maintenance activities.(30)
More specifically, SiWIM data—including axle loads, gross vehicle weights, axle spacing, speed, vehicle class, lane of travel, and time and date of passage—have been or are now being used to support the following activities:
- Bridge structural assessments
- Bridge safety assessments
- Aggregate and site-specific traffic loading
- Dynamic loading
- Load testing
- Road planning
- Special transport applications
Bridge structural assessments. For bridge structural assessment, three questions are of interest:
- What is the carrying capacity of the bridge (i.e., age, condition)?
- How does the bridge really behave (i.e., influence lines, traffic load distribution)?
- What is the real loading (i.e., dynamic amplifications)?
Using traditional procedures, new bridges are designed very conservatively because of uncertainties about future traffic loading conditions and the expense of adding capacity after construction (i.e., adding capacity during the initial construction process is relatively inexpensive). Proper assessment and monitoring can prove that many existing bridges are safe in their current condition for their current loading, justify optimal rehabilitation measures, and save significant money on unnecessary or premature rehabilitation.
For existing bridges, capacity and loading can be measured and monitored directly using bridge WIM to avoid unnecessary or premature rehabilitations. Bridge WIM can provide both improved traffic loading data and improved structural data (to support the determination of influence lines, load distribution factors, and dynamic amplification factors). The use of SiWIM systems is being investigated as a tool for optimized assessment in a larger project, Sustainable and Advanced Materials for Road Infrastructure (SAMARIS), involving 23 partners and 16 countries.
Bridge safety assessments. Bridge safety assessments verify that a structure has adequate capacity to safely carry or resist specific loading. SiWIM system data have been used to determine current bridge capacity and safety under specific loading conditions.
Aggregate and site-specific traffic loading. SiWIM has been used to demonstrate different aggregate traffic loading patterns in various countries in Europe.
Dynamic loading. Historically, the dynamic amplification factor (DAF)—the ratio between maximum dynamic and static loadings—has been conservatively assumed in bridge structural design. The use of models to improve the accuracy of these factors is time consuming and difficult because of many unknowns. Bridge WIM can be used to improve the estimation of DAFs. In initial investigations, the DAFs using SiWIM data for extreme load cases are considerably lower than those specified in the design codes.
Load testing. Load testing of bridges is required when:
- Seemingly sufficient bridges fail to pass assessment calculations
- Bridge models do not adequately match the behavior of the real bridge (i.e., optimization of the structural model)
- Data about the bridge structure are insufficient.
Load testing can optimize bridge assessment by finding reserves in load-carrying capacity, often resulting in less severe rehabilitation measures, fewer traffic delays, and significant cost savings. Traditional load testing, using preloaded vehicles, is costly to perform and may result in damage to the structure. SiWIM systems can support "soft" load testing using normal traffic data and the observable structural behavior of the bridge.
Road planning. Traffic loading calculations to support road planning typically rely on the use of expansion factors applied to finite traffic count samples. These factors are often obsolete and do not account for overloading. In Slovenia, traffic loading estimates using SiWIM system data compared to estimates using traditional traffic loading calculation methods differ in the range of minus 10 percent to plus 278 percent (e.g., in the worst case, the pavement carried almost three time heavier traffic loading than was planned during its design).
Special transport applications. SiWIM systems are being used to calculate the safety of a particular bridge or bridges under special transport loading using the exact axle loading and axle spacing. In addition, these systems are being used to field verify OS/OW movements remotely.
In Switzerland, commercial motor vehicle weight and size data are collected at the national level and compiled in FEDRO's Road Traffic Management Information System (MISTRA) database. The WIM-system data include axle configuration, vehicle type, individual axle load, and gross vehicle weight. Only vehicles weighing in excess of 3.0 metric tons are stored (calibration is limited to vehicles over 3.5 metric tons). These data are voluntarily shared with internal customers, research institutes, contracted engineer offices, and domestic and international customers. There are no regulation-based data-sharing obligations.
Historically, these data have been used to support the following:
- Preselecting overweight vehicles during enforcement activities
- Determining the need for enforcement of overloaded vehicles
- Determining damage factors and road usage for dimensioning roads and bridges, with a particular focus on trans-Alpine goods traffic
- Renovating engineering structures
- Attaining the Swiss Transitioning Policy (i.e., Goods from Road to Rail)
- Related research efforts
The sufficiency of data quantity (i.e., geographic coverage, sample sizes) and level of detail are the topics of investigations as part of WIM Concept Switzerland. With these investigations still underway, no formal guidance or standards exist on commercial motor vehicle size and weight enforcement data collection and quality.
WIM system data, available from 40 sites in Germany, are largely used to support statistical reporting and special scientific investigations. Aggregate data include axle and gross vehicle weight frequencies in several load classes and the number of overloaded vehicles, in addition to more routine traffic data.
Data collected from the Toll Collect system in Germany are largely underused. This newly introduced system has significant potential to provide systemwide, route-specific, or segment-level commercial motor vehicle data. When asked if the data were being used for any purpose other than administering tolls, Toll Collect representatives indicated that the government owned and would determine the future of the data. Data are being captured and stored, however, with the understanding that there may be a potential future application outside of toll collection.
In the Netherlands, commercial motor vehicle size and weight data from six sites are collected in a central database maintained by the Ministry of Transport. These data are provided, by request, in a variety of formats Microsoft®, Excel®, Adobe® PDF, XML, HTML) and unfiltered or filtered according to vehicle size, vehicle weight, vehicle status (e.g., overweight), vehicle class, etc., depending on need.
At least weekly, the quality of the data is reviewed. A data quality statement is issued each week to police officials, who use the data to schedule their mobile enforcement efforts. These quality statements include the number of axles measured and compared to static weights, the period of measure, and the inaccuracy for every weigh point. If any unusual change in data quality is observed, the problem can be quickly remedied. In general, vehicle classification data have error rates ranging from 2 to 4 percent. Error rates for the WIM system cannot exceed plus or minus 2 percent for speed and plus or minus 15 percent for axle load for 95 percent of the vehicles measured (in aggregate).
While the data quality is carefully monitored, the limited geographic coverage precludes a wider application of the data. Example applications, should more WIM systems be installed nationally, include monitoring of the following:
- Overloaded heavy freight vehicles on the national level
- Goods traffic on the national level (not just overloaded vehicles)
- Transportation of dangerous goods on the national level (WIM can be used to identify hazardous material transporters and pull them in for either further inspection or identification)
The Dutch recently used the data from the WIM/VID systems to monitor special transports via desk research. Nearly 40 percent of the special transports observed did not, in fact, possess the appropriate paperwork. In this application, these observations were viewed as an educational opportunity.
Recently, Rijkswaterstaat (part of the Ministry of Transport, Public Works, and Water Management) started to more actively monitor the effectiveness of commercial motor vehicle size and weight enforcement efforts, identify any related problems and needs, and work with partner agencies to resolve issues. This effort, entitled the Business Intelligence Monitoring WIM (MoWIM) Project, provides a mechanism for assimilating, monitoring, and mining WIM data and generating guiding reports to help achieve the project's objectives of reducing overloads by 20 percent per year on the national highway network (in the proximity of WIM systems only).
As part of this project, monthly reports from the National Police Agency, the Transport Inspectorate, and the Ministry of Transport are entered into the MoWIM database. Reports include the following:
- Total GVW and axle overloads by month, WIM site, and type of vehicle (used to direct officer-based selection procedures)
- Number of static measurements per employee per week, month, and location (used more to evaluate enforcement site functionality (i.e., how far do trucks have to travel to reach the site?) than officer performance).
A reduction over time in the amount and frequency of weight overages suggests benefits from enforcement efforts.
In the Walloon Region, the Ministry of Infrastructure and Transport has developed a long-term policy for collecting detailed traffic data on roadways under its jurisdiction. This data collection activity is being largely accomplished by the six WIM systems now in operation. These systems provide reliable statistics on heavy goods vehicle traffic and the weights transported, supporting roadway design and maintenance efforts in the region.
France has an extensive national traffic monitoring system, SIREDO (Système Informatisé de REcueil de DOnnées), that collects data to support both real-time traffic monitoring and non real-time transportation planning. SIREDO includes a national network of 1,830 data collection stations, 170 of which include WIM systems for weight capture. Loops and pressure cells are used to count vehicles and axles and to record speed, vehicle length, headway, and mean speed. Some stations also collect weather information and axle weights. The geographic coverage and the level of data available from SIREDO are unparalleled in the other countries visited.
For statistical planning purposes, the Ministry of Transport receives summary reports annually or more frequently by request. Other data applications require more frequent reports, and data are transmitted to traffic management centers every 6 minutes for near real-time display. France has also explored alternative uses of WIM data. Jacob explored the use of WIM data to:
- Support the calculation of fatigue damage and bridge lifetimes(31)
- Calibrate the conventional fatigue load models in the codes (and Eurocodes)(32)
- Check existing bridge reliability.(33)
Altogether, most of the motorway concessionary companies installed about 50 WIM systems on the network to collect weight data throughout the year. The data are used to assess heavy vehicle traffic intensity and loads and to plan pavement maintenance or replacement operations. Moreover, these data provide useful tools for the motorway operation.
Comparison/Contrast with the United States
Similar to the United States, European countries use real-time WIM data most often for preselection during enforcement operations. With few exceptions, however, the United States has not fully realized the potential of using WIM data to schedule the best days, times, and locations for optimum mobile enforcement. One concern in the United States is that widespread use of WIM data for enforcement could disturb the integrity of the planning data (because truckers will bypass). This application was widespread in the countries visited, and this practice has only been experimentally studied in a limited fashion in the United States.
The accuracy and portability of bridge WIM systems have the potential to cost effectively generate significantly more field-based weight and load data for pavement, bridge, and asset management than is now generated in the United States. In addition, the unique data applications (i.e., special transport certification and verification) demonstrated in Europe may have merit.
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