The Introduction and Implementation of Mobile Retroreflectivity Measurement of Pavement Markings in Ireland

Retroreflectivity describes the ability of a road/pavement marking to reflect light back to its source and is critical in ensuring the safety of road users, especially in low-light conditions and at night. It is assessed by... [ view full abstract ]

Retroreflectivity describes the ability of a road/pavement marking to reflect light back to its source and is critical in ensuring the safety of road users, especially in low-light conditions and at night. It is assessed by measuring the coefficient of retroreflected luminance (RL), which is a measurement of reflection under vehicle headlamp illumination. In other words, RL is a measurement of the brightness of the pavement marking, as seen by drivers of motorised vehicles in vehicle headlamp illumination at night time.

Research was undertaken to investigate the suitability of mobile retroreflectivity equipment for the evaluation of pavement markings in Ireland and to identify a suitable system which would best cope with the unique challenges posed by Irish road and climate conditions. Equipment from various worldwide manufacturers were investigated and following this research, the LTL-M Retroreflectometer was identified as a suitable system and was acquired for a trial period. The LTL-M Retroreflectometer is mounted on a vehicle (in this case a van), allowing surveys of line markings to be undertaken at normal traffic speeds. A suitable control/test site was identified and extensive data was collected through a wide range of conditions. Two different methods were examined, using the LTL-M and using a handheld retroreflectometer. One of the requirements from the research trials was to establish a good correlation between the LTL-M and the handheld monitor. Also, the repeatability of the LTL-M system from multiple runs on the same day and reproducibility over time (multiple runs over different days) were established. With a bank of control site data established during the trial period, data was subsequently collected on approximately 7500 km of line markings on different sites spread throughout Ireland using the LTL-M. This included repeat runs in different climatic conditions and along pavement marking laid in opposite directions onto the road surface.

This paper describes the research carried out into mobile retroreflectivity equipment, in particular, outlining the findings of the research study undertaken using the LTL-M. This includes an analysis of the range of data collected using the LTL-M, establishing its correlation with the handheld retroreflectometer and the repeatability and reproducibility of the LTL-M. In addition, the paper will outline the research into the effect that climatic conditions, in particular moisture, can have on the RL results of line markings and the effect that the direction in which the pavement marking is laid onto the road surface has on the RL results.