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The humps, in Forth St, Union St East and Harbour Tce, were installed in September to slow motorists and improve the safety of pedestrians and cyclists in the busy student area.
However, motorists have been driving around or between the humps.
Council transportation safety team leader Hjarne Poulsen said the council had been monitoring the speed humps since their installation, and while speed had reduced, changes needed to be made.
''We have noticed motorists avoiding the speed humps in a couple of locations and will be installing additional sections to widen them in these areas.''
Mr Poulsen said the extensions would be straightforward as the humps were only bolted to the ground and did not require any road excavation.
However, a gap would remain.
''There will still be a [1.2m] gap between them. We are keeping a gap to allow buses to drive over the speed humps with their wheels running on either side.
''A car will not be able to go through without hitting the speed humps,'' Mr Poulsen said.
Otago Polytechnic communications director Mike Waddell said the polytech supported the council's decision.
''Widening the speed humps makes good sense.
''After all, it is about people's safety, which is our No1 priority.''