Heavy tow overdimension testing

The issue of overdimension vehicle towing is closer to being resolved, thanks to a day of tests in Auckland in September 2020.

The problem arises when very heavy and possibly lengthy vehicles – often fuel tankers or car carriers – break down or are damaged and require towing to a safe place. These tows are well outside the general access limits in the Vehicle Dimensions and Mass (VDAM) rule.

It was once normal practice to break down the heavy vehicle, perhaps by unhooking the trailer. But this is sometimes difficult or impossible with newer combinations and can mean the tow truck and the vehicle it is towing, with a combined length of up to 37 metres and weights approaching 80 tonnes, need to travel longer distances. Questions then arise over safety and legality.

There was discussion about heavy vehicle towage during Heavy Haulage forums organised by Waka Kotahi during COVID-19 lockdown. From those meetings a group was formed to investigate the issue and that led to the testing in Auckland involving industry, Waka Kotahi and Transport Engineering Research NZ (TERNZ).
Carr and Haslam Transport offered two trucks and the company’s yard for the day of testing. Bonney’s Transport provided two trucks and the heavy tow truck was supplied by Ace Towing. A day of rigorous testing was undertaken and filmed. Low-speed testing took place in the yard, and the trucks went on to the roads for higher speed testing.

TERNZ was commissioned to do a desktop exercise concerning heavy vehicles under tow and to look at how the rest of the world has approached this issue. This information would help Waka Kotahi finalise a permit policy for these tows.

Read the TERNZ report [PDF, 2 MB]