The Road Ahead : April May 2007
relocated or reduced in severity. A MR spokesperson said decisions about barriers are made on site characteristics, such as road alignment, number of lanes, speed limit, 85th percentile speed (85 percent of traffic at or below a road speed), crash histor y, barrier deflection and safety per formance, vehicle types and installation/ maintenance costs. She said there could be different barriers on the same road due to changing safety standards, the emergence of new products and their per formance in different circumstances. "The decision on which type of barrier to use is not based on cost, but on the suitability of the barrier to the specific location where it is to be installed," the spokesperson said. About 37 percent of Queensland's national highways still have unsafe roadsides, according to the Australian Road Assessment Program (AusRAP). According to RACQ's executive manager traffic and safety John Wikman, barriers themselves posed risks. "Barriers are not the be all and end all, because they still pose a risk to road users," Mr Wikman said. "However, we'd encourage greater spending on all roadside improvements, including barriers with appropriate end treatments, given the tragic consequences of hitting an unprotected roadside hazard." Barriers are considered for all new roads, however existing roads only get attention when upgraded, or audited. Road specialist, QUT's Professor Rod Troutbeck, said engineers could not design roads without barriers. "Bridges need a barrier, for example, and another situation that we can't have is traffic heading into an oncoming lane. We are becoming more concerned about cross-median accidents," Prof. Troutbeck said. "You tr y to find the best site for it (a barrier) but at the same time you've got to realise a barrier is going to increase the risk of more crashes. "You may install a barrier to cover a hazard that may not be hit ver y often, and the barrier itself may be hit more often. "In a crash, unfor tunately a lot of energy has to be effectively managed. The stiffer a barrier, the more a car has to absorb." resort 'W' or thrie beam Semi-rigid barrier steel rail mounted on steel posts, resembles a 'w' turned on its side. Deforms, absorbs energy of an impact and redirects a vehicle when struck but retains its strength and should prevent a vehicle from passing through. Should be more than 20 m long to shield an object or redirect vehicles. End treatments need to be carefully managed for head-on impacts. Rigid barriers Fixed concrete barrier normally used on narrow median treatments. Should retain shape and position when struck. End treatments are critical. Essentially maintenance free but can cause higher indirect costs (up to 10 times more than wire rope) as impact is usually more severe. Can cause secondar y crashes as impacts may redirect vehicle back into traffic. Crash barrier costs All barriers are designed to last for 20 years. Typical installation costs are: wire rope $150 per metre, W-beam guardrail $250 per metre and concrete barrier $500 per metre. Each crash into W-beam costs around $6000 to repair, versus $4000 for wire rope and minimal cost for concrete. safety barriers APR/MAY 07 9 Gordon Hoole (left) and John Murphy, from Basic Construction Ser vices, measure a new barrier on Wynnum Road, Tingalpa.
June July 2007