The weight limit was agreed following a series of meetings on Thursday involving Dunedin City Council staff, and would be in place once signs were installed next week.
The decision follows consultants' investigations into the structural integrity of the bridge, which rested on wooden piles as it crossed the Silver Stream near the Taieri Airfield.
The bridge was not in imminent danger of collapse, should one of the piles give way, but the three-tonne limit was deemed to be necessary to protect the bridge, council communications co-ordinator Rodney Bryant said.
Council transportation operations manager Graeme Hamilton said no decisions had been made about the bridge's future.
The matter would be discussed at an upcoming infrastructure services committee meeting on November 24, before being considered at the next full council meeting on December 15, he said.
Options still under consideration included repairing or replacing the bridge, or doing nothing, and cost estimates - which were not available yesterday - would be presented to councillors at the upcoming meetings, he said.
Council staff had earlier signalled their intention to down-grade the bridge to pedestrian use only.
A new bridge would be built over the Silver Stream when the planned Carncross St-Centre St extension was constructed as part of the transportation plan for Mos-giel's arterial routes.
