However, it has no plans for major road works to improve safety at the bridge, just south of Oamaru.
There have been two crashes at the bridge this month - on May 1 when a truck hit the concrete abutment, spilling part of its load, and on May 10 when a car struck a bank on the approach, then rear-ended the abutment.
Fourteen crashes - no fatalities or serious injuries and nine minor injuries - have been reported to police in the past 10 years.
That has led to calls for safety improvements.
But Transit NZ's acting regional manager in Dunedin, Bruce Richards, said there were no plans to carry out major work there.
"Doing that would be very expensive and it would not stack up in terms of the cost-benefit ratio."
However, Transit had listened to submissions by Oamaru police about limiting the speed at the bridge.
It agreed it was too fast at 100kmh and would be preparing a report which would go to the New Zealand Transport Agency Board in July, recommending speed be reduced to 80kmh.
In addition, next week it would be erecting new signs at the overbridge, two chevron arrow boards on the north side, one on the south side and large width markers on the abutments, including across the top.
Mr Richards did not know how far the new 80kmh would stretch along SH1.
That would depend on the findings of the report, which was also looking at a request for an 80kmh speed limit from the boundary of Oamaru to the southern end of the Alma straight, which included the overbridge.
Dunedin truck driver Nathan Anderson, who was driving his owner-operated unit on May 1 when it hit the bridge, does not believe the signs and a reduced speed limit goe far enough.
He plans to campaign to have major work carried out.
Yesterday, he maintained that was still the answer.
He is commissioning a report from a specialist crash investigator on the overbridge, which would be used in his campaign.
"People already slow down going under the bridge, but there are still accidents," he said.
Oamaru police highways patrol Sergeant Pete Muldrew had promoted the lower speed limit, but emphasised it was the individual driver's responsibility to drive safely.
The highway patrol had been targeting the bridge and people who failed to keep left and crossed the centre line.
Transit said the carriageway under the bridge was 7m wide. The distance between the abutments was no less than 7.4m.
The maximum width of a truck (excluding its mirrors) was 2.5m, leaving only 2m on the carriageway for trucks to pass under the bridge, or 2.4m between the abutments.
