AP-G84/04 Best practice in road use data collection, analysis ... - WIM

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Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005 Input raw data Add calendar information Fit linear model Run Hidden Markov Model 7+ days block of bad data found? Remove these bad periods from data Refit linear model Austroads 2004 — 44 — Best Practices in Road Use Data Collection, Analysis and Reporting Run outlier method Predict missing counts If hourly aggregate to daily Output Figure 13 – Flow diagram of the CSIRO method for detection of corrupt traffic data 6.4 Calibration of a WIM System Table 18 shows the range of (high-speed) WIM technologies employed in Australia (Koniditsiotis 2000). These technologies include plate-in-ground, load cell, piezo-cable and strain gauge. The supplier/manufacturer of a WIM system will provide detailed instructions for calibration. In view of the fact that most of the WIM sites in Australia employ CULWAY, with 142 in operation in year 2000, this section therefore uses CULWAY as an example to illustrate some aspects of good practices in WIM calibration. Again, each RA has its own operational guidelines on CULWAY installation and operation and it is unnecessary to repeat the full procedures in this report. CULWAY weighs and classifies traffic by using mechanical strain gauges deployed in a box culvert. Vehicles passing over the culvert cause the roof to deflect producing strain forces that can be converted to axle loads. The CULWAY system employs two piezoelectric sensors, placed 10 m apart in each instrumented lane to detect vehicle passage and synchronise the strain measurement at each axle. The accuracy of CULWAY relative to other WIM systems currently in use is also shown in Table 18. CULWAY and all other WIM sites should be carefully calibrated to achieve optimal use of the system.
Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005 Austroads 2004 — 45 — Best Practices in Road Use Data Collection, Analysis and Reporting This section highlights one general aspect and one specific aspect in the use of CULWAY: General guidelines on site selection; and Corrections for the time-dependent drift between calibrations. Table18 – High-speed Weigh-in-Motion Systems Used and available in Australia (source: Koniditsiotis 2000) Mass sensor type Bending plate Load cell Piezoelectric cable WIM system name PAT DAW100 ARRB TR HSEMU ARRB TR Expressweigh Installation mode Semi-permanent flush mounted Semi-permanent flush mounted Permanent flush mounted Strain gauge ARRB TR CULWAY Semi-permanent within pavement culvert installed Max. no. of lanes 4 User-defined 2 1 to 4 Axles weighed Weighing capacity for axle load (tonnes) All All All All 20 80 - 50 Temperature (°C) -40 to +75 -20 to +70 -50 to +80 -10 to +70 Sensor life span (years) Accuracy Vendor 3 rd party Installations in Australia (as reported in year 2000) − 15 − 10 *GVM (± 10% at 95%) − 10 (another 6 using other bending plates) GVM (± 5% at 95%) GVM (± 3% at 66%) GVM (± 10% at 95%) − GVM (± 10% at 95%) GVM (± 7% at 95%) 2 1 140 (another 2 for multilane operation) * GVM (±10% at 95%) means that the accuracy of measuring gross vehicle mass is ±10% for 95% of vehicles weighed. 6.4.1 Site Location The selection of a suitable location for a CULWAY installation is critical to the accuracy of the information collected. The following criteria (from Main Roads WA) are recommended when assessing the suitability of a site for CULWAY: (a) Alignment and overtaking opportunities - a minimum of 120 m of straight and level roadway should be on each side of the CULWAY. Sight distance should not be so good as to make it an attractive overtaking opportunity for motorists. This encourages poor lane discipline resulting in poor detection rates and low levels of data confidence. Avoid placing CULWAY too close to curves since vehicles travelling at speed may swing wide taking the curve and consequently affect the CULWAY results by invalid vehicle actuations. (b) Longitudinal grade - ideally the longitudinal gradient shall be less than 1%. However, the gradient may exceed this where considered appropriate but gradients of more than 2% are not suitable.
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AP-G84/04 Best practice in road use data collection, analysis ... - WIM

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