Transmission Gully

PHOTO: Transmission Gully. Photo: Supplied / Waka Kotahi / Mark Coote

Road surfacing reports released by the Transport Agency show attempted repairs to Transmission Gully actually made the highway worse.

Two reports undertaken by the engineering consultancy firm Stantec on behalf of Waka Kotahi showed extensive stretches of flushing on the southbound lanes, and some flushing on the northbound lanes.

Flushing is a pavement surface defect which results in a smooth surface texture.

In hot weather, the binder in a flush surface can become sticky and soft and in wet weather the area can be very slippery.

The report identified that in an effort to rectify the issue loose chip had been spread over the affected areas.

“It is understood the intention is for some of the Grade 5 chips to stick and for a few to pick up and remove a small portion of the excess bitumen. The intention is agreed with, but while the flushing is generally in the wheel tracks in many places few of the loose chips were in the wheel tracks,” the report said.

An observation was made that an attempt to roll the loose chip with steel drum rollers was not effective.

“Close inspection of the chip seal after rolling by steel drum showed some chips had been crushed while other chips had their tops broken off. Bonding of the loose Grade 5 chips to the excess bitumen was not apparent. Breaking the tops off the chips in the chip seal would reduce the texture depth of the seal.


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