"We set ourselves high standards with our contracting processes and the public can have confidence in our activities.
"We have a good record in this area and will always take any allegations of issues seriously and investigate them thoroughly."
It was immediately clear in this instance that some of the allegations were factually incorrect, while others required deeper investigation, Mr Quinn said.
However that investigation also found there were no issues to answer, he said.
"We are pleased that the PwC report and SFO decision not to investigate further confirm that our processes are robust and that organisations we work with can have confidence in any arrangements with KiwiRail."
All the people involved were open and forthcoming throughout the investigation and handled the process with professionalism, Mr Quinn said.
"We will not be releasing the report or commenting further to protect the reputation of these people from these unfounded allegations.
"We are now hopeful that these unfounded rumours will cease."
A KiwiRail spokeswoman declined to comment on the exact nature of the corruption allegations.