Abstract
Drivers rely on the visibility of pavement markings to maintain a safe road path especially during nighttime and challenging weather conditions. With the growing demand for pavement marking materials, durability and long-term weatherability of these products is critical. Current performance evaluation methodology using field test-deck protocols requires significant time and resources, and under these protocols the performance of a pavement marking can be monitored for a period of up to three years. In addition, safety-related issues such as exposing technical staff to road hazards while applying the marking materials and collecting measurements, along with road closure consequences, are of concern. The primary objectives of this research were to develop an accelerated laboratory-based procedure that could evaluate the performance of pavement markings, overcome the shortcomings of current evaluation practice, and investigate the safety performance of pavement markings based on existing crash data and results from a driver simulation study.
For the laboratory-based procedure, a three-wheel polisher device (TWPD) and xenon arc chamber (XAC) were employed to replicate varying traffic, snowplowing, and weather conditions. The deterioration of the physical measurements (i.e., dry and wet retroreflectivity, color change, and durability) of waterborne and thermoplastic markings was modeled. All of the performance measures logarithmically deteriorated under different TWPD loadings, except for the durability of the thermoplastic markings which followed a linear degradation function. A significant reduction in percent retroreflectivity was observed in the initial part of the TWPD testing but leveled out as the number of cycles increased. This deterioration pattern is similar to what occurs in the field, as retroreflectivity dramatically decreases after the first few months of installation and then stabilizes before the end of its service life. On the other hand, a linear increase in retroreflectivity and color change occurred during the artificial weathering exposure time (i.e. 2,000 hours) due to the change in surface physical properties. The color analysis revealed an important relationship between pavement marking retroreflectivity and color change. After traffic loading, all colors darkened due to the exposure of the black asphaltic color or the abrasion of the upper layer of marking, and in turn retroreflected less light while different color change patterns were experienced under the artificial weathering.
The color analysis results showed that when a color closely resembles white, the sample retroreflected more light. The TWPD and weatherometer effectively simulated and accelerated the operational and environmental effects (e.g., traffic, snowplowing, sunlight, moisture, and temperature) so that assessment of pavement marking performance could be completed in an abbreviated time frame. The results yielded a significant relationship between all performance measures assessed in both the laboratory and field. Evaluating the performance of pavement marking products using an accelerated laboratory-based procedure provides a department of transportation (DOT) with a flexible tool to cope with the rapidly evolving industry through the establishment of guidelines that might be used for the selection and maintenance of the pavement markings. This procedure can be used to compare different marking materials and assess marking materials whether they bear severe traffic operating conditions or harsh climates before implementation.
To assess the safety performance of pavement markings, specifically on two-way, two-lane rural roads which are common in the state of Idaho, two separate approaches were adopted. First, a crash analysis study over eight years (2010-2017) on rural roads in Idaho was conducted to understand the relationship between retroreflectivity deterioration of edgelines and crash occurrence. Field retroreflectivity data for waterborne edgeline markings from thirty-eight sites were collected and modeled over twelve months across six districts with different environmental conditions. The results yielded a logarithmic relationship between retroreflectivity and age, and pavement markings in districts subjected to higher ground snow loads deteriorated faster than those with lower ground snow loads. This faster deterioration trend in northern districts was attributed to winter maintenance activities and harsh weather. Even though, a clear statistical pattern was determined for District 1, which was subjected to the higher ground snow loads among all districts, the methodology used in this study could not definitively conclude that crash rate increased with lower edgeline retroreflectivity.
Second, a study using the University of Idaho’s driving simulator was implemented to evaluate the safety effects of different edgeline pavement marking widths (e.g., 4-inch and 6-inch) and deteriorations (e.g., 0%, 25%, 50%, and 75% deterioration) on driver behavior. The results indicated that statistically significant differences were observed during nighttime conditions when comparing the driver’s lane deviation (vehicle’s lateral position) between the wider 6-inch longitudinal edgeline pavement markings and standard 4-inch edgeline marking. Drivers consistently maintained a lane position that slightly favored the edgeline side when exposed to a 4-inch marking and increasingly shifted away from the centerline as edgeline deterioration worsened. The results of the statistical analysis implied that 4-inch markings and severely deteriorated pavement markings cause higher variation values in driver lateral position which in turn could affect overall driver safety.
This research benefits transportation agencies, particularly those sited in cold-weather regions, by enabling them to predict the deterioration of marking materials and assist in the scheduling of maintenance marking projects to maximize the operational and safety benefits of the existing material. This research also make recommendations with regard to a minimum retroreflectivity threshold that should be maintained for pavement markings of two-way, two-lane rural roads and the use of wide pavement markings.