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 Austroads 2004 — 6 — Best Practices in Road Use Data Collection, Analysis and Reporting Figure 3 - Typical response of a loop detector crossed by a passenger car Two types of loop designs are commonly used by road authorities for vehicle counting on a lane of traffic flow. A loop for counting at mid-block is often a square loop of 2 m × 2 m, and a pair of these loops at a known distance (4 - 5 m) apart is usually used for speed measurement and vehicle classification. A second loop design is the SCATS loop for signal operation and traffic counting. The SCATS loop has a width of 2 m and an overall length of about 4.5 m and is located near the stopline of an approach. It provides reasonably accurate counts over a measurement period of, say, 15 minutes but the counting accuracy is less over the length of a signal cycle of one to two minutes due to the loop location and length. For accurate counting, care needs to be taken in selecting the size, shape and positioning of the loop within the traffic lanes. Over-counting can occur when loops in adjacent lanes are too close and the same vehicle is detected in both lanes. On the other hand, motor cycles or small vehicles, straddling both lanes may be missed by loops placed too far apart. The ability of the loop detection circuit to hold the change in inductance (or electric charges) allows a loop sensor to be a presence detector. This property allows a loop sensor to measure volume and speed at very low speed and is therefore suitable for congested urban traffic conditions. However, speed measurement using loops is not as accurate as axle sensors due to more uncertainty in the actuation timings. This also affects the accuracy of vehicle classification using a pair of loops. The classification has to be by vehicle lengths and in a smaller number of classes or bins (see Section 3.3). Also, inductive loop detectors are not suitable for unsealed roads in general. 3.3 Vehicle Classification System Vehicle classification data is important for all transport engineering applications. Comprehensive classification data is now possible using new technologies. Vehicle classification surveys are concerned with the distribution of traffic data into different types of vehicles. Classified data can be used for design and performance of road pavements and bridges, traffic capacity and operations analysis, vehicle categories for traffic legislation and regulation, road safety studies, and economic studies.
Accessed by AR - ARRB TRANSPORT RESEARCH on 04 Feb 2005 Austroads 2004 — 7 — Best Practices in Road Use Data Collection, Analysis and Reporting A number of classification systems are currently in use. These systems include the 1994 Austroads system (Table 2) and a few other systems mainly for urban traffic, which are also shown in Table 3. Table 2 - Current Austroads vehicle classification systems (updated in 1994) Level 1 Level 2 Level 3 Length (indicative) Axles and Axle Groups Vehicle Type Austroads Classification Type Axle Groups Description LIGHT VEHICLES Class Parameters Short Up to 5.5m 2 1 or 2 Medium 5.5m to 14.5m Long 11.5m to 19.0m 3, 4 or 5 3 Short Sedan, Wagon, 4WD, Utility, Light Van, Bicycle, Motorcycle, etc. Short – Towing Trailer, Caravan, Boat, etc. 1 2 d1 ≤ 3.2m and Axles = 2 Groups = 3, 2.1 m ≤ d1 ≤ 3.2m d2 ≥ 2.1m, and Axles = 3, 4 or 5 2 2 HEAVY VEHICLES Two Axle Truck or Bus 3 d1 > 3.2m and Axles = 2 3 2 Three Axle Truck or Bus 4 Axles = 3 and Groups = 2 > 3 2 Four Axle Truck 5 Axles > 3 and Groups = 2 3 3 4 > 2 5 > 2 6 > 6 > 2 3 Medium Combination > 6 4 17.5m to 36.5m > 6 5 or 6 Long Combination Over 33 m > 6 > 6 Three Axle Articulated or Rigid vehicle & trailer Four Axle Articulated or Rigid vehicle & trailer Five Axle Articulated or Rigid vehicle & trailer Six Axle (or more) Articulated or Rigid vehicle & trailer 'B' Double or Heavy truck trailer Double Road Train or Heavy truck and trailers Triple Road Train or Heavy truck and three trailers Definitions: Group: (axle group) - where adjacent axles are less than 2.1m apart Groups: number of axle groups Axles: number of axles (maximum axle spacing of 10 m) d1: distance between first and second axle d2: distance between second and third axle 6 7 8 9 d1 > 3.2m, Axles = 3 and Groups = 3 d2 ≤ 2.1m, 2.1 m ≤ d1 ≤ 3.2 m Axles = 4 and Groups > 2 d2 ≤ 2.1m, 2.1 m ≤ d1 ≤ 3.2 m Axles = 5 and Groups > 2 Axle = 6 and Groups > 2 or Axles > 6 and Groups = 3 10 Groups = 4 and Axles > 6 11 Groups = 5 or 6 and Axles > 6 12 Groups > 6 and Axles > 6
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AP-G84/04 Best practice in road use data collection, analysis ... - WIM

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