What’s two tonnes? The 48T question


NZ Transport Agency Freight Portfolio Director Harry Wilson addresses the request for a 48MAX truck configuration.

Harry Wilson

We received great feedback at the recent Road Transport Forum (RTF) conference on the work we are doing to remove the road blocks to greater use of high productivity motor vehicles (HPMVs). Most of the main barriers to the greater use of HPMVs are being addressed, both in terms of infrastructure access and regulatory barriers.

One curly request raised by a few road freight operators at the conference, and in discussions since, was the possibility of a 48-tonne version of 50MAX using the large number of 8 axle combinations already in the national fleet. Like 50MAX the request is that these 8-axled combinations have near network-wide access at 48 tonnes.

While this sounds great for productivity and road safety, unfortunately it is a non-starter for value for money due to the infrastructure impacts.

In permitting HPMVs the Transport Agency and local councils are required to consider the durability of roads and bridges on which the vehicle may operate. This is to ensure that the economic value of freight productivity gains is not offset, or even overshadowed, by additional infrastructure costs.

In this case a 48-tonne eight axle combination will have a much greater pavement impact than a 50MAX. This is down to simple maths with the pavement impacts from 48 tonnes spread across eight axles, against 50 tonnes being spread across nine.

Due to the disproportionately greater pavement impact from heavier axles, 48 tonnes on eight axles is a non-starter for much of the network as it would create significant road maintenance costs that are likely to outweigh the economic benefits. An increase in weight per axle of around 8%, for example, would result in around a 36% increase in pavement wear. This impact would be greater on local roads. 50MAX, on the other hand, does not increase pavement wear due to having an additional ninth axle.

Because of this the Transport Agency is not looking at allowing 48-tonne area-wide permits for heavy vehicle combinations with 8 axles. Instead freight operators can apply for 48-tonne HPMV route-specific permits where the infrastructure is suitable to allow access to heavier vehicles. HPMVs with 8 axles will also be able to travel at higher mass on the High Productivity Freight Network – which is being delivered through the current National Land Transport Programme. This network will provide near continuous HPMV access across 4,500 of New Zealand’s busiest freight routes on roads suitable for these heavier trucks up to 58 tonnes.

Harry Wilson
Freight Portfolio Director
NZ Transport Agency