MRWA developed a bridge based strain gauge system called AXWAY in the 1980s.

Experience with AXWAY led MRWA, in conjunction with ARRB, to develop Culway (Austroads 2000).

With Culway, strain gauges were mounted onto a culvert rather than a bridge (as shown in the figure below).

Figure: Culway site and Culway II data logger

Fig 5.1

Source: ARRB

Culway has been installed in many culvert sites in most states and territories. In 2000 Austroads reported that amongst the 170 WIM sites in Australia, 140 were Culway sites.

The figure below shows a schematic layout of a Culway installation with the following main components:

  • Strain sensors: these are attached to the roof section of an appropriately sized box culvert.
  • Two axle detectors: piezoelectric cables are embedded in the road surface. These are placed at a set distance apart, one over the centre of the culvert in which the strain sensors are placed and the other at a known distance (10 m in Western Australia) upstream. The axle detectors provide data for vehicle classification and speed and are also used to trigger the recording of strain data as each axle passes over the culvert.
  • Data logger: this is either battery or mains powered. The logger stores information on each vehicle such as strain measurements, axle count, speed, and axle spacing. From these can be calculated information such as vehicle class, ESAs, axle configuration, gross vehicle masses and axle masses.
  • Portable computer: is typically used to set up the data acquisition system while on site. It may also be used to carry out some processing and reporting functions.
Figure: Elements of a Culway vehicle weighing system

Fig 5.2

Source: Adapted from Austroads 2013.

The Culway system generally operates unattended with data being periodically retrieved when the recording capacity of the unit is reaching its limit. This is generally about 10 000 vehicles or about two weeks' duration, depending on battery life and other factors.

The data is typically retrieved by appropriate telemetry using data modems, avoiding the need for regular site visits.

Some Culway systems now operate with solar power and are particularly useful at remote locations.

ARRB Culway has been improved and upgraded continuously.  The currently available product is named Culway II.  Culway II is a two-lane, high speed WIM system that uses sensors installed within a box culvert to unobtrusively monitor traffic.  It can accurately collect volume, speed, classification and mass data.  Culway II measures and records up to two lanes of data and the Culway II can directly replace the old single lane Culway units. 

ARRB is currently working with SRAs to increase logger memory capacity and to provide a new download, processing and QA software package.

The table below provides the specifications for Culway II.

Table: Culway II specifications
Item Specification Comments
Number of lanes 2 Enable upgrade of existing sites to 2-lane operation
Storage Approx. 10 000 vehicle records per lane  
Outputs Data in Culway raw data (CRD) format Fully compatible with original Culway format
Primary WIM sensors Up to 8 Culway mechanical strain amplifiers ( MSAs) 4 MSAs per lane attached to the culvert to provide vehicle mass measurements
Auxiliary detectors Up to four auxiliary traffic detectors (two per lane) Installed in the road surface to provide accurate vehicle classification data
Weight measurement error < ±10% of the static gross vehicle weight with 95% confidence  
Conformity Conforms to ASTM E1318-02 Type I requirement  
Communications 2XRS232 serial ports – (modem or laptop) Upgrades for additional ports if required
Power source Nominal 12V DC, 0.5 amp  
Operating temperature 0 °C– 60 °C  
Enclosure Environmental protection –IP65  

Source: ARRB.

 Further Reading

Austroads 2013, Guide to Traffic Management Part 3: Traffic Studies and Analysis, Appendix G, AGTM03-13, Austroads, Sydney, NSW.

Austroads 2000, Weigh-in-motion technology, AP-R168-00, Austroads, Sydney, NSW.

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