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
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
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.
The table below provides the specifications for Culway II.
Table: Culway II specifications
|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|
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.