This story has been corrected to remove incorrect references to the tracks being laid too close together and some areas within a 16km section of track near South Featherston being laid on average 4mm narrower.
KiwiRail will begin work to resolve issues on the Wairarapa line at the end of this month, following the completion of an independent investigation.
The investigation into the Wairarapa vibration issues, undertaken by Beca, recommended rail grinding and reprofiling the wheels of the Wairarapa carriages as the key steps to resolve the vibration issues.
Greater Wellington Regional Council said work to fix the Wairarapa train line would not be able to done until a fire ban in the region was lifted.
Now it has been, KiwiRail general manager Jon Knight said grinding the tracks will be the first phase of work.
"I appreciate how frustrating it has been for Wairarapa locals since we put speed restrictions in place last year to manage these vibration issues, which resulted in longer journey times," he said.
"The vibration in the Wairarapa are caused by issues with how carriage wheels are interacting with the rail.
"Grinding the new rail with our specialist machine is our first step to fix the problem.
"We will have our grinder in Wellington to start work on 26 May.
"Grinding the 40km of track between Featherston and Masterton will be done at night, when passenger trains aren't running.
"We will start in the areas where there are vibration issues, and the total distance should take about eight weeks to complete."
Knight said grinding was a standard maintenance practice, and should help the track and carriage wheels fit better together.
"It's something we have been planning to do for months but, given the amount of sparks grinding generates, the summer fire ban in the Wairarapa made that impossible.
"With the ban lifted, we can now get our grinder down to Wellington and get the work done."
The report also found that the new Wairarapa track was installed correctly to KiwiRail’s national standard and was within its acceptable engineering tolerances.
It found that the tolerances on the new Wairarapa track were a significant improvement on the old track, which was many decades old. The tolerances were a lot more consistent and within the correct range, compared to the older track which varied widely between being too loose and too tight.
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