About weigh-in-motion

Heavy vehicles can be weighed on static scales (JPG picture 91 Kb), on low-speed weigh-in-motion scales at weighing stations, which are driven over at a speed up to 15 km/h, or on portable weighing pads, which are placed under the tyres of the truck. While these weighing procedures are suitable for controlling and fining overloaded vehicles, they are less appropriate for traffic data collection. On static scales only a very small percentage of freight vehicles is weighed. Low-speed weighing stations are rather expensive to set-up and to maintain. They usually operate only few hours per day and are therefore easily avoided. A great part of the heaviest, most representative trucks is therefore not recorded. The same problem is even more emphasized with the portable weighing pads.

On the other hand, high-speed WIM systems provide continuous unbiased weighing of practically all vehicles passing the system. They are also imperceptible which means that the drivers are not aware of the weighing operation and do not try to avoid it.

Today there are approximately 1000 working WIM stations around the world of which approximately 450 in the United States, 300 in Europe (GIF picture 23 Kb, 1999) and 150 in Australia. They are also used in South Africa, South Korea, Israel and in some other countries.

WIM systems are generally divided into:

• permanent (sensors and the data acquisition systems collect data at the same location),

• semi-permanent (sensors are built into pavement while the data collection system is moved from site to site), and

• portable (sensors and equipment are moved from site to site).

According to the type of sensor, the weigh-in-motion systems are using:

• bending plates (JPG picture 91 Kb),

• bar sensors (JPG picture 111 Kb), such as piezo-ceramic, capacitive or quarz sensors,

• capacitive mats (JPG picture 112 Kb) or

• existing bridges - bridge weigh-in-motion systems.

Photo gallery

Last updated on 17^th of July, 2006, by A.Znidaric