High Speed Weighing
The Griffith Elder Highway Weigh-In-Motion system uses three rows of very high accuracy Quartz Sensors to detect and weigh each axle of every vehicle. The axle weights are automatically added together to give axle group weights and gross vehicle weights.
A dual wheel sensor detects the width of the tyres and whether there is a dual wheel on an axle. An inductive loop ensures that each vehicle is recognised separately from the next vehicle. An automatic camera records the license plate which is held together with the weight information of the vehicle so that the classification of the vehicle can be determined automatically. The camera can have software for European, Arabic, Chinese or other language license plates.
If required, variable message signs can be used to tell vehicles what to do after being weighed.
The Quartz Sensors are the heart of the High Speed Weigh-In-Motion system. Manufactured from the highest quality natural quartz, the sensors detect the weight of each wheel as it crosses them in the road. Three rows of sensors are used in each lane of the highway to give the most accurate weight of each axle as it passes. Times between sensors give the speed of the vehicle and distances between axles.
High Speed Weighing - Features
3 rows of Quartz Sensors for high accuracy
Maximum axle weight 30 tonnes
Sensor overload capacity 45 tonnes per axle
Gross weight accuracy + - 5%
Vehicle Speed 3 to 130 km/hr
License plate recognition camera
Automatic vehicle classification
Speed accuracy + - 1 km/hr
Dual wheel sensor
Induction Loop to recognise new vehicle
Database to store results
High speed weigh in motion operates between speeds of 3 and 130 kilometres per hour. Traffic traveling between these speeds will automatically be caught by the HSWIM system.
Sensors in the road are Quartz and compliment the inductive loop sensors, which recognise vehicle separation, to detect axle weights as a vehicle drives over them. Typically the Quartz Chrystal Piezoelectric sensors are accurate to within 10% on a single axle and within 5% on the gross vehicle weight, and are generally acceptable for deciding which vehicles should be directed off the road to a weigh-station. However, in some countries they are accepted as being suitable to prosecute overweight vehicles because the tolerance is such that the 5% discrepancy works in favour of the vehicle owners.
Sensors are usually arranged in sets of six in each lane of the highway to give maximum accuracy. In order to work with highest accuracy the road surface needs to be within certain tolerances which are detailed within the EU document COST 323. It should be noted that local installation conditions will influence accuracies.
A single Dual Wheel Sensor is normally also installed with the HSWIM sensors so that classification can be correctly determined, including double wheeled axles.
One of the major uses of High-Speed Weigh-in-Motion is to decide which vehicles should be pulled off the highway to be further examined. Normally this is due to infringement in weights allowable, however in recent times more interest has also been shown in taxation and insurance infringements and vehicle size (height and width) discrepancies. All these aspects of vehicles can be determined using In-Highway equipment to detect the vehicles fully. Each vehicle can be looked up in a national database and former infringements of the regulations can be noted in real time, so the personnel at the weigh-station will know, in advance of when a vehicle arrives, what they are looking for.
CCTV surveillance systems are often used in conjunction with the in-highway monitoring systems to give detailed video evidence of the presence and defects of a vehicle. This is usually stored separately from the national database of vehicles due the large size of files created at each weighing site. However, with appropriate software both systems can be viewed in synchronised time so that the video reinforces the data collected for each vehicle which is being investigated.
Information on the Single-Axle Low-Speed Weigh-in-Motion system can be found in the document named Single Axle Overload Detection.
Vehicle Counting Function
Apart from weighing vehicles, the induction loop and the dual wheel sensor together can be used as a reasonably priced vehicle counting, vehicle speed, and classification system, with vehicle density and road use statistics easily developed from the data collected. The data is stored in a database at the road station and can be retrieved either at site using a laptop to plug into the data logger, or via Ethernet using a remote connection.
Data Transfer to Central Database
The Industrial Computer program sends all records to a central database, in real time, as they are completed from each WIM station. The data transfer program runs in the background and automatically tries to send a record as it is completed. In the event of no communication with the central database it will keep trying until a connection is made. It will then send all records that have been completed since the last good connection.
The normal method of data transfer is across the internet. To ensure the data cannot be intercepted or corrupted all data is encrypted between head office and the outlying stations.
The Central Database collates all the results from the individual roadside stations so that reports from the central database can include vehicles that have visited more than one station. For instance it is possible to report on a particular vehicle to see how often it is in contravention of the weight limit rules. Or, a report could be run to detect a particular company to check on what has been delivered.