Official papers show more than 150 State Highway bridges have been earthquake-strengthened in the past decade.
Since seismic strengthening began about 10 years ago, bridge linkage upgrades and retrofits have been undertaken on 156 bridges.
Transport Agency spokesperson Andy Knackstedt says the work has cost $27 million.
He says inspections on the 20 retrofitted bridges in Canterbury following the powerful September earthquake showed the work contributed to their lack of damage.
Mr Knackstedt says it's estimated about $30 million will be available for seismic strengthening nationwide in the next five years.