Capital Projects:

The primary function of the weigh in motion system is to help establish a Bridge Specific Loading for the bridge. 

Under national technical standards, long span bridges such as Forth can use a Bridge Specific Loading rather than adopt the usually more onerous national assessment standard load.  However, its use is governed by the need to check the loading every two years.

The weigh in motion system works by dynamically weighing each and every vehicle that crosses the bridge in both directions.  The system can also used to classify and count vehicles to in order to provide traffic statistics

The existing system was installed in 2000 in the north rock cut, set within both northbound and southbound carriageways.  Similar systems were installed on the M74, Erskine Bridge, Tamar and Tay Road Bridges. 

All these systems were based on dynamic weigh pads installed in the carriageway.  Unfortunately, these plates have proved to have a short service life and have had to be replaced or reinstated in both carriageways.  The resulting downtime of the system has caused significant problems in both establishing the bridge specific loading and traffic counting.