Five years after the danger posed by ageing bus and coach tyres was highlighted horrifically by a fatal coach crash on the A3 trunk road in Surrey and subsequent inquest and coroner’s report, controversy continues to rage.

This month, following a welter of criticism of repeated Tory blocks on proposed tyre-age legislation, transport minister Jesse Norman commissioned Berkshire-based TRL (formerly the Transport Research Laboratory) to carry out a £250,000, twelve-month research project designed to “provide a fuller picture on the safety of tyres as they get older.”

Frances Molloy is unimpressed, describing the move on the BBC’s Victoria Derbyshire programme as a government delaying tactic which “doesn’t go far enough”. Molloy is the mother of Michael, the 18-year-old coach passenger who was killed in the 2012 crash, together with 23-year-old Kerry Ogden and the 63-year-old driver Colin Daulby. The inquest in 2013 heard evidence from a distinguished accident investigator that the sole cause of the crash was a tyre blowout on the steering axle. The tyre was 19.5 years old, 2.5 years older than the coach itself.

Molloy met Jesse Norman last summer, shortly after he became transport minister. Since then her local Member of Parliament, Labour’s Maria Eagle, introduced a bill that would have made it unlawful for tyres over ten years old to be used on buses and coaches. The bill’s passage through the House of Commons was blocked by Conservatives. An earlier bill put forward by Steve Rotheram, now mayor of Liverpool City Region, had suffered a similar fate.

Molloy sees the latest government-commissioned research as “an expensive delaying tactic.”

Can age be solely responsible for tyre failures?

It certainly is clear already that commercial vehicle tyres can fail suddenly and sometimes catastrophically for a host of reasons other than age, including punctures, botched puncture repairs, severe impacts and chronic overheating caused by under-inflation. So how could the Surrey coroner and his expert adviser be sure that the sole cause in this case was tyre age?

We put that question to the expert, David Price of Bristol-based Forensic Accident Investigation Services (FAIS), about five years ago, shortly after the inquest.

“I can’t say 100% definitely that age was the cause of the tyre failure,” he conceded candidly, before going on to explain that he nevertheless concluded that it must be after ruling out all other possible causes through a process of elimination.

There was no doubt that the tyre had been delaminating before the crash. Price found no evidence of impact damage, of any kind of puncture repair, or of any manufacturing defect. There was also no doubt about the tyre’s age, revealed by the sidewall code demanded by the US Department of Transportation (DOT).

Price explains that this coding format changed in the year 2000. Before then a mixture of symbols and digits was used. Since then a simpler four-digit code has taken over, with the first two digits denoting the week of manufacture and the last two the year. So “1902” on a tyre sidewall means it was manufactured in week 19 of the year 2002.

The coach tyre that blew out on the A3 in 2012 had been manufactured in 1993, yet its tread was only half-worn and it had been neither regrooved nor retreaded. So the tyre had either been a spare or in storage for years.

There is no doubt that all tyres deteriorate with age, but the rate of that deterioration varies enormously with exactly how the tyre is used or stored. Price describes the Merseypride Travel coach tyre that failed with such catastrophic consequences as “abnormally old” and he certainly would advise strongly against use of a tyre of this age on any commercial vehicle, especially on steer axles.

But he stops short of agreeing with calls for the introduction of specific legal limits on tyre age, pointing to independent tests in the US which sought to quantify the effect of ageing on risk of tyre failure. Price would like to see similar tests conducted in the UK, together with research into the age profile of tyres currently in use on various types of vehicles.

Legal liability issues complicating matters

Graham Willson, managing director of the British Tyre Manufacturers’ Association, described the question of tyre age limits five years ago as “a bit of a Loch Ness Monster that keeps rearing its head from time to time.” Ozone and ultra-violet light are the main enemies of tyres as they age, he reckoned.

“European manufacturers tend to agree on a ten-year age limit, but our legal friends don’t make it easy,” he said. “In North America, they avoid any numbers altogether because of the risk of endless product liability claims.”

The BTMA’s technical committee published recommendations on tyre service life in June 2010, and updated them in May 2012 (six months before the A3 coach crash). The recommendation is for car, 4×4, van and commercial vehicle tyres, including spares. It says: “The serviceability of a tyre over time is a function of the storage conditions (temperature, humidity, position etc) and service operating conditions (load, speed, inflation pressure, road hazard damage, climatic conditions, terrain, etc) to which a tyre is subjected throughout its life.

“Since these conditions vary widely, accurately predicting the serviceable life of a tyre in advance is not possible. The longer the tyre has been in service, the greater the chance that it will need to be replaced, due to service-related deterioration, or other conditions found upon inspection or detected during use.”

A Michelin technical bulletin on truck and bus tyre age and condition agrees, unsurprisingly, with the BTMA, but is a little more specific.

“Tyres in service, including spare tyres, for five years or more should continue to be inspected by a specialist at least annually,” it says. “Operators are strongly encouraged to be aware not only of their tyres’ visual condition and inflation pressure, but also of any change in dynamic performance such as increased air loss, noise or vibration, which could be an indication that the tyres need to be removed from service.”

Derek Godden is managing director of Lasalign, a long-established Leicestershire-based company specialising in commercial vehicle wheel, axle and chassis alignment. His observation surely should be heeded by every fleet manager and transport engineer making decisions about which tyres to fit and where.

“Every tyre tells a story,” he says. “Just think of the consequences of its sudden failure when deciding whether or not any tyre is too old to use.”