2Presentation Outline Applications of WIM WIM classification WIM detector technologiesBending Plate WIMPiezo-Electric WIMSources of error in WIM dataSummary
3WIM Definition“The process of measuring the dynamic tire forces of a moving vehicle and estimating the corresponding tire loads of the static vehicle”American Society for Testing and Materials (ASTM) Standard Specifications E
4WIM ApplicationsProvides reliable and accurate data on the weight and types of vehicle using roadsWIM data can be used for:Weight enforcementData collection ►Industrial / military
5Data Collection“Understanding "why" some pavements perform better than others is key to building and maintaining a cost-effective highway system.”Long Term Pavement Performance (LTPP) program — a comprehensive 20-year study of in-service pavements.
6Broad Classification of WIM Low speed systems (<15 km/h)Provide the high level of accuracy needed for enforcement or toll collectionHigh speed systems (>15 km/h)Minimize or eliminate vehicle disruption while permitting data of sufficient accuracy for planning and screening
7Classification of WIM (According to Installation Type) PermanentSensors and the data acquisition systems collect data at the same locationSemi-permanentSensors are built into pavement while the data collection system is moved from site to sitePortableSensors and equipment are moved from site to site
8WIM Components Accurate weighing device - weighpads or axlepads Very high speed A/D converter to change the voltage signal into required dataSoftware package for data collection and analysis
10Bending Plate WIM Steel rubber plates w/ strain gauges Generated signal proportional to the deflection of the plate under a vehicle axleSignal is amplified and processed to produce the vehicle axle mass
11Bending Plate WIMTypically consists of two in-road weigh platforms in a travel laneInductive loop vehicle detectors before and after bending plate scales
16Bending Plate WIM Other Information CostIn-ground: $15K to $85K Portable: $18K to $22KExpected Lifetime: 8 to 12 yearsAccuracy (individual axles and GVW)In-ground: 0 to12% ±1SD Portable: 0 to 6% ±1SDVendorsIn-ground: International Road Dynamics, International Traffic Corp., Pat America, Inc. Portable: Pat America, Inc.
17Piezo-Electric WIMPiezoelectric materials convert mechanical stress or strain into proportionate electrical energythese materials mechanically expand or contract when voltages of opposite polarities are appliedPiezoelectric polymer films are also piezoelectric, converting heat into electrical charge
18Piezo-Electric WIMPermanent or temporary installation into or onto the road surfaceCan be installed directly into the road in a flexible formatCan conform to the profile of the roadFlat construction, small cut
20Piezo-Electric WIM Other Information Cost$3K to $60K AccuracyIn-ground: 3 to 30% ±1 SD Portable: 3 to 30% ±1 SD VendorsIn-ground: Cardinal Scale Manufacturing Co., ECM, Inc., International Road Dynamics, International Traffic Corp., Kistler Instrument Corp, Pat America, Inc., Peek Traffic, TDC Systems Portable: ECM, Inc., International Road Dynamics, International Traffic Corp., Peek Traffic
22SummaryWIM detectors are becoming increasingly popular for collecting traffic data at highway speedsSeveral technologies of WIM detectors exist to collect accurate and quick traffic dataSelection of WIM depends on applicationGood installation and calibration of WIM required for accurate and reliable data