The Transport Department is working to repair a section of the O-Bahn track amid concerns that the 27-year-old piece of infrastructure is nearing the end of its expected lifespan.

In late 2012, the Transport Department permanently reduced maximum speeds on the entire O-Bahn from 100 km/h to 85 km/h.

While the department insists the speed cut related to safety concerns, transport insiders believe wear and tear on the track means slower running is necessary.

A former transport department chief says it’s amazing the concrete track has lasted this long.

The Transport Department is currently working to re-level a small section of the O-Bahn to fix the issue.

A spokesperson for the Transport Department told InDaily linked the slower speed limit to safety concerns.

“A risk review after the most recent accident on the O-Bahn track recommended a reduction in the maximum speed,” the spokesperson said. “As a result, all buses on the O-Bahn have been speed limited to 85 km/h.

“A risk review was undertaken in November 2011 after an incident on the O-Bahn in April 2011. The permanent speed reduction of 85 km/h was recommended to lessen the impact of any accident that may occur and consequential damage and to also improve the chances of a bus driver being able to recover control of a vehicle should circumstances necessitate.

“It was implemented in late 2012 and has only added less than 20 seconds to the average run.”

However, at least one bus contractor has linked the vibration issue to lowered speed limits, InDaily understands.

According to one source briefed on the issue, the head of one bus contractor has pointed the finger at Adelaide Metro’s former fleet of Mercedes articulated buses.

Mercedes buses were first used on the O-Bahn when it was opened. These buses were later replaced with a new fleet of Scania and MAN buses.

According to the source, bus operators have complained that the Mercedes buses left a significant groove on the O-Bahn’s concrete track through repeated wear.

The new buses have a slightly different wheelbase, meaning they are not “in sync” with the groove – causing “significant” vibrations, according to InDaily’s source.

There has been internal debate on whether the issue is a design flaw in the track or in the buses, InDaily understands.

Former South Australian Transport Department head Derek Scrafton, now an academic at the University of South Australia, estimated the track – built in 1986 – had a working life of about 30 years.

Scrafton said the track had so far exceeded expectations, but was now getting towards its use-by date.

“In all fairness, we’re talking now about 27 years since the first stretch was opened,” he said.

“You’d normally think about a track like that having a 30 year life, like a railway.

“It is amazing that is has lived up to what the developers, the German engineers said it would.”