Structural monitoring installed at the truss end links of the structure show the bridge can now allow a limited number of HGVs to cross – up to around 600 northbound between 11 pm and 4 am nightly, starting February 4, 2016 subject to weather conditions.

The structural monitoring systems installed on the bridge provide live data on the behaviour of the bridge to inform decision making and modelling while 90 per cent of traffic has been crossing successfully since the reopening. The information from the monitoring systems has shown that phase two of the repair work to strengthen the bridge needs to be completed in full to the main span locations before the bridge can fully reopen to HGVs.

The impact of high wind and wet weather has limited the opportunities to carry out this sensitive phase of the repairs. Preventative works are also required at two other pin locations. Consequently, the bridge is now scheduled to be fully reopened to HGVs with no restrictions by mid-March, instead of mid-February as initially planned.

A dedicated HGV lane and stacking area will be in operation to help manage the traffic flow across the bridge. Traffic signals will release HGVs on to the bridge at a rate of one every 30 seconds. The release rate has been calculated by engineers as the optimum rate to maximise the number of vehicles able to cross whilst minimising the impact on the structure.

Subject to weather disruption, the trial will monitor the behaviour of the structure throughout the process, the outcome of which will determine whether the number of HGVs being allowed to cross the bridge can be increased.

Transport minister Derek Mackay said: “This is a phased reintroduction of HGVs to the Forth Road Bridge which aims to provide access to the bridge at the earliest available opportunity. Allowing limited access to the bridge when traffic is lighter will hopefully provide some relief to local hauliers while repair work continues.

“90 per cent of traffic returned to the Forth Road Bridge in December and while we recognise that around 600 HGVs crossing the bridge each night does not get us to 100 per cent, it is a step in the right direction – with full reopening expected in mid-March. We will of course continue to explore every option to see if we can increase access as the trial develops.

“The information from the monitoring equipment is providing a detailed picture of how the bridge is behaving to inform our decision making and modelling. We will not take any decision which could risk damaging the bridge or compromising safety, so we have taken the decision to push back the reopening of the bridge to HGVs to allow time for phase two of the repair work to be complete, with additional time added as contingency due to the effects of the weather.

“The expert engineering advice we have received, indicates that with phase two of the works complete, the bridge will have sufficient strength to cope with normal loading of HGVs alongside other traffic.

“Every effort is being made to carry out the repair work as quickly as is possible. When the phase two strengthening works are complete the bridge will re-open to HGVs with no restrictions.”

Chartered engineer and Amey’s account director for the Forth Road Bridge, Mark Arndt, added: “During the recent storms, the bridge has been closed to traffic, at times, because wind speeds have been so high and it wouldn’t be safe to have people out working in those conditions. Our teams are working flat out to complete the work necessary to fully reopen the bridge but our timetable is highly dependent on the weather and our priority has to be on safety.”