Estimating the effect of run-out length on w-beam construction costs in Queensland

An investigation into various road safety barrier run-out length methods and the estimated cost differences due to resulting 'length of need' differences is presented. The study establishes an automatic calculation method for a large number of geometric scenarios and achieves this by developing regression algorithms for clear zone, shy line offset and run-out length. The algorithms are implemented into computer code to calculate 'length of need' for road safety barrier for straight roads and roads with horizontal curves from 100 m to 1000 m radius. Clear zones are calculated with variable fill slopes and also include a clear zone adjustment factor on the outside of horizontal curves. Hazards are located at various distances from the edge line for curved roads, and at the outer edge of the calculated clear zone for straight roads. Barrier offsets are set to 1 m for all roads, and also at the calculated shy line offset for straight roads. In total, 11 605 geometric scenarios and the differences in 'length of need' due to different recommended run-out lengths are calculated. Cost differences are estimated assuming a base cost of installing standard w-beam road safety barrier. Overall it is estimated that reducing recommended run-out lengths could reduce costs by approximately A$4000 for one-way road installations.