Structural monitoring installed at the truss end links of the bridge reveals the structure can now allow around 600 northbound HGVs to cross between 11pm and 4am, subject to weather conditions.
However, the phased re-introduction means the full reopening of the FRB has been delayed by a month.
The structure was closed to all vehicles over Christmas after damaged steel work was discovered on 23 December.
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The structural monitoring systems installed on the FRB provide live data on the behaviour of the bridge to inform decision making and modelling.
While 90% of traffic has been crossing successfully, the systems have shown phase two of the strengthening repair works needs to be completed on the main span locations before the bridge can fully reopen to HGVs.
Due to adverse weather conditions and preventative works required at two other key locations, the bridge is now scheduled to reopen by mid-March.
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.
"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."
(LM)
