The hidden persuaders

Heard and felt rather than seen, rumble strips are being used increasingly to deter drivers from running off the road or crossing the centre line.   BY GAVIN RILEY

Rumble.jpgEfforts to lower the road toll in New Zealand tend to focus on the numbers killed each year and to publicise punitive measures taken against two of the main perpetrators: speeding and intoxicated drivers.

Much less publicity is given to the number of injury accidents and another worrying group of road users, fatigued or inattentive drivers who run off the road or cross the centre line.

Yet on the state-highway system alone, which constitutes a mere 11 percent of the nation’s 90,000 kilometre roading network, there were nearly 4000 loss-of-control or head-on crashes in 2005 – an alarming statistic given the Ministry of Transport says $461,000 is the average social cost of a fatal or injury accident in a rural environment. 

Fortunately, a simple strategy is being employed to help keep drivers on the straight and narrow; to deter them from careering off the road into culverts, ditches and power poles, or across the centre-line into the path of oncoming vehicles.

The strategy is the use of audio tactile profiled markings – known to the motoring public simply as rumble strips because of the noise heard and sensation felt by drivers when their vehicles encounter one.

Rumble strips were first used in Britain as a safer-motoring device in 1985 and appeared in New Zealand before the end of that decade in a trial on Mt Eden Road in Auckland.

Their use in this country, mainly as edge-line warnings on motorways, remained relatively minor until 2004, since when Transit New Zealand has implemented a major safety initiative that includes spending about $4 million annually on rumble strips. Other road-controlling authorities are also funding installation of the strips following the realisation they can be employed effectively on no-overtaking centre-lines of two-lane rural roads.

This more extensive use gathered momentum after Transit’s published summary just over two years ago of research findings showing the strips helped reduce crash rates. The research included a ‘Review of Lane Delineation’ report in 2004 by a Transport Engineering Research New Zealand (TERNZ) team, which stated that:

• Reports of rumble strips’ effectiveness had shown a  two to 44 percent reduction across all types of crashes, with an average reduction of 27 percent.

• Shoulder rumble strips had reduced “run off road” crashes by 20 to 80 percent, with an average of 32 percent (42 percent for fatal crashes).

• Centre-line rumble strips had lowered reported head-on and sideswipe crashes by 21 to 37 percent.

• Centre-line rumble strips produced movement of vehicles away from the centre-line.

• Rumble strips appeared to retain their effectiveness, unlike other road-safety measures, which declined in value as their novelty wore off.

The report also said wider edge-lines and centre-lines produced consistent improvements in drivers staying within marked lanes, particularly young, elderly and intoxicated drivers.

Following these findings, Transit undertook further research into rumble strips as part of its South Waikato and Taupo State Highway 1 road safety corridor improvement project.

This 200 kilometre section of State Highway 1 had an unacceptable crash problem with 54 fatal and 84 serious injury crashes in the five years to 2004.

“The line marking did not stand out and the edge of the road was not easily identifiable. The driving task was demanding,” reported Transit national safety engineer Colin Brodie, who led the research team and whose work earned him last year’s 3M traffic-engineer-of-the-year award for safety innovation from the Institute of Professional Engineers.

Addressing the TERNZ recommendation that edge and centre lines be widened, Brodie proposed widening rumble strips from 100mm to 150mm, placing them on double yellow centre lines with 100mm between the lines to create a 400mm-wide painted ‘barrier’, and laying them immediately outside edge-lines to form a 300mm-wide strip. Such measures also produced increased visibility in adverse driving conditions – a significant benefit given that 63 percent of the near 4000 loss-of-control or head-on crashes on state highways in 2005 occurred during poor weather.

Brodie reported that the system his team had devised had been laid as a trial on 94 kilometres of the South Waikato and Taupo section of State Highway 1 and on 92 kilometres along State Highway 2 between Katikati and Tauranga. Preliminary and anecdotal evidence indicated the system was proving effective in reducing high-severity crashes, and thus it was being extended along the State Highway 1 section.

“There is a growing acknowledgement that fatigue and inattention are a greater safety concern than previously recognised,” Brodie said.

Despite this, extensive use of rumble strips on the nation’s roads is not quite a foregone conclusion.

A Land Transport New Zealand research report, released in July and prepared by TERNZ, said profiling of edge-lines and no-overtaking centre-lines tended to be applied where there was an obvious history of injury accidents, and there might be the potential to treat a larger proportion of the country’s rural roads.

“However, the cost-effectiveness of these safety improvements needs to be calculated before their more widespread use,” the report cautioned.

It pointed out that the materials used in applying rumble strips, ATP thermoplastic and cold-applied plastic, were more expensive than those used in laying conventional flat lines, leading to a trade-off between cost and safety.

Placing the cost of rumble strips at $7500 a kilometre, TERNZ considered they provided significant safety benefits which outweighed the treatment costs even at relatively low traffic volumes. Accordingly, TERNZ recommended that the profiled markings be applied on a much more widespread basis where road conditions allowed “and policy changes should reflect this”.

Not surprisingly, the implications of a major increase in the use of rumble strips were discussed at this year’s New Zealand Roadmarkers’ Federation annual conference.

“A number of points were raised: how much is going to be put down; where is it going to be put down; and if you’re going to buy, what scale of plant will you need – a small walk-behind machine, a large unit, or do you go for super low-tech?” says federation executive director Alister Harlow. 

He says five of his organisation’s members (based in Whangarei, Auckland, Rotorua and Dunedin) were currently applying rumble strips – but at least another four were in the process of commissioning plant.

Machines applying ATP thermoplastic are made in UK and the United States, however one Auckland company is making its own machinery. Machines delivering cold-applied plastic are European-made. The materials themselves are supplied by two New Zealand and two Australian manufacturers.

Harlow says the use of rumble strips could be described cynically as creating a poor man’s highway.

“We can’t afford to build the [appropriate] carriageways, yet this offers opportunities round that. It offers safety benefits because effectively you’re creating semi-fences in terms of both the edge and the centre of the carriageway.”

There are three powerful pointers to rumble strips playing an increasingly important role in creating a safer roading network.

One, Land Transport’s TERNZ research report estimates that currently no more than three to five percent (300-500 kilometres) of the state highway network has had rumble strips applied. But it says even if a benefit-cost ratio of 4.0 were used as a minimum criterion for application, 70 percent of the network would qualify for some degree of treatment.

Two, Transit says its South Waikato and Taupo State Highway 1 safety-improvement project (which incorporates the use of rumble strips) is part of the Government’s nationwide initiative to reduce annual road deaths to fewer than 300 by 2010.

Three, the motorist’s champion, the Automobile Association, intends promoting greater use of rumble strips in its safer-roads campaign.

The AA’s general manager for motoring affairs, Mike Noon, described Land Transport’s TERNZ research findings as “sensational” and added: “The benefit-cost ratios are extraordinarily high, and extremely high in areas like narrow bridges. It [the report] starts to address a real problem we have, so that now if you do fall asleep or you do lose attention, rumble strips are the silent policeman.

“It [rumble strips] is not the only answer. But it looks on the basis of that study that it is a valuable contribution to road safety that hasn’t been fully exploited.”

Contractor Vol.31 No.9  October 2007
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