Electric and double-decker buses damage roads more than diesel, report finds

By Phil Pennington of RNZ

Heavier double-decker and electric buses are damaging roads more than the usual diesel buses, requiring higher-strength repairs, according to NZ Transport Agency Waka Kotahi (NZTA).

While this might be the case on the state highways overseen by the transport agency, the situation was less clear on local roads, with two of the three biggest bus operators not looking into it.

“We have not investigated if, or been made aware of, whether the weight of our fleet is having an impact on the roads,” said ECan, which runs buses in Canterbury.

“Greater Wellington has not examined whether the weight of its fleet is damaging roads,” said Metlink, which runs the capital’s buses.

Auckland Transport said it was monitoring the issues, but would not say what it had found out about it.

The transport agency raised its internal warning flag earlier this year, saying an increase in loads on roads was forcing it to renew surfaces sooner and with tougher treatments.

“For local roads, heavier double-decker buses and electric buses are also causing more rapid decay on bus routes.”

Auckland Transport said electric buses were not necessarily heavier than diesel, although some of the early electrics needed overweight permits.

“We are continuing to monitor the impact of double-decker buses and electric buses, and other heavy vehicles on the road network,” it said.

“To prevent wear and tear on the road surface, we are now using a stronger and stiffer asphalt concrete using harder binder when making asphalt, concrete, and chip seal.”

NZTA has said something similar: “The increase in traffic loading... causes more rapid deterioration of infrastructure, bringing forward the need for renewals and increasing the robustness of the treatments we must use.”

It had been reporting back to funding decision-makers about the risks it faced from “high outgoings” on road maintenance.

Auckland Transport said it was monitoring the issues and an increase in loads on roads was forcing it to renew surfaces sooner and with tougher treatments. Photo / Sylvie Whinray

State highway maintenance was 48% over budget at $1.2 billion, and local road maintenance 23% over at $800 million, earlier this year.

The Government then ordered what it said was more than double the usual state highway repairs this summer.

Most bus routes are on local roads that councils looked after – although NZTA subsidised their repair – but many go down state highways.

Metlink said some localised damage had been noted around bus stops.

“But given the combination of a heavier Metlink fleet, road use by other heavy vehicles, adverse weather events and water damage and maintenance practices to Wellington’s roads, it is difficult to attribute a cause.”

It forecast more of the same problems, saying zero-emission buses were heavier than diesel and heaviest during peak hours.

“It is anticipated that over time, public transport fleets will get heavier as more high-capacity buses and zero-emission buses are added to fleets to maximise capacity and minimise transport emissions.”

Bus weights are dropping, as battery technology improves.

The maximum weight was when buses were fully loaded, said ECan.

“This typically only occurs at peak times and for short durations, given people are constantly boarding and disembarking.”

Auckland Transport said double-deckers and electric buses were both essential. “We are on a mission to electrify our bus network... we currently have more electric buses than any Australasian city.”

Electric buses will start paying road-user charges from the start of 2026.

Metlink said that, unlike NZTA, it could not directly access the road-user charges that help fund roadworks.

“Metlink’s fleet operates predominantly on roads controlled and funded by territorial authorities. However, territorial authorities do not access the funding via the RUC [road user charges] paid to NZTA directly.

“The solution to road maintenance is access to appropriate levels of funding for road controlling authorities,” it said.

The Bus and Coach Association industry group said an electric bus operating with the same design and footprint as a diesel could weigh three tonnes more.

There were other options, but cut-price contracts were getting in the way, chief executive Delaney Myers said.

“Lighter buses that cause less damage can be deployed but they come at a higher cost point,” Myers said.

“And the challenge with that is that the councils award contracts based primarily on the lowest price, which then of course impacts the purchasing decisions that the bus companies make.”

Contracts were not factoring in the road damage from heavier buses, even though that “is something NZTA and council roading staff have been well aware of since their introduction”.

“That’s not deemed as a priority by the councils who are contracting it.”

It was a “false efficiency”.

“If you factor in things like road damage, it’s highly likely that buying that cheap bus up-front is a far more expensive option than investing in better technology in the first place.”

Myers had been talking about this with councils and NZTA for well over a year, with no sign yet of lighter buses being bought, she said, adding the impetus had to come from the councils as purchasers of the services.

Bus contracts should also take into account emissions during construction and “ethical manufacture”, she said.

The public feedback to various transport consultations by government agencies has largely said that heavy vehicles should contribute more towards the costs of road maintenance and improvements.

– RNZ

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