Low-Cost Traffic-Calming Road Markings on Sharp Downhill Curves: A Driving-Simulator Comparison of Perceptual Treatments

Perceptual road markings are widely used to manage approach speed at curves, but the supporting evidence comes largely from moderate radii and their behaviour on sharp descending curves remains untested. This study evaluated three low-cost treatments, a checkerboard pattern, red peripheral transverse bars and red-coloured transverse bands, on two real hairpin curves of radii 22.7 and 26.0 m on a Spanish mountain road, reproduced in a fixed-base driving simulator. Twenty-four drivers completed four fully counterbalanced scenarios; speed, lateral position, and longitudinal acceleration were recorded at eleven stations from 250 m upstream to 50 m beyond each curve. The treatments reshaped the spatial profile of speed but did not improve lateral control. The coloured bands advanced deceleration: after adjustment for upstream baseline speed, drivers were 4.8 km/h slower where the first band began, achieved entirely over the preceding 50 m, before the band was crossed. After the same adjustment no treatment differed from the base scenario within the curve, and peripheral transverse bars produced no measurable effect at any station. On sharp descending curves a full-lane coloured band acts as a visual gate that brings braking forward, whereas peripheral optical treatments effective on moderate curves do not transfer to this geometry.