Project Summary Report 0-4150-S Project 0-4150: Evaluation of Pavement Marking Effectiveness Authors: H. Gene Hawkins, Jr., Timothy J. Gates, Elisabeth R. Rose Pavement Marking Effectiveness and the Pavement Marking Handbook Pavement markings provide one of the primary means of communicating information to road users. Unlike traffic signs and signals, pavement markings are continuous and provide road users with valuable information that helps them properly position the vehicle within the travel way. Pavement markings are different from signs in another way: pavement markings are typically manufactured at the location where they are applied instead of being manufactured in a factory and sent to the installation site. As a result, there is the opportunity for greater variability in the performance characteristics of pavement markings. Pavement markings are a primary means of communicating with road users. What We Did … This project evaluated several Pavement Marking all who wished to attend. The key characteristics associated with Conferences many individuals who attended (139) heard presentations from the retroreflective performance of During the first year of the marking experts with other state pavement markings. There were project, The Texas Transportation transportation agencies, the five major activities associated Institute (TTI) hosted two Federal Highway Administration, with this project: pavement marking conferences and industry. Primary issues that to identify and discuss important • conduct of two conferences issues associated with pavement were discussed at the conferences on pavement marking markings in Texas. Key pavement included: thermoplastic application performance, marking stakeholders in Texas, on sealcoat surfaces, striping • evaluation of pavement including many Texas Department inspection, performance and marking retroreflectivity on of Transportation (TxDOT) warranty pavement marking flexible pavements (hot-mix representatives, attended these specifications, and de-bonding of asphalt and surface treatments), conferences. The first conference thermoplastic from concrete. was an invitation-only meeting • identification of pavement Markings for Flexible marking use on rigid held in College Station with a pavements (concrete), limited number of individuals Pavements (35) that was intended to identify Providing long-lasting • evaluation of the measurement what the major pavement marking of marking thickness, and thermoplastic pavement markings challenges are. on surface treatment (sealcoat) • development of the Pavement surfaces has become a challenge Marking Handbook. The second conference was held in Austin and was open to for some TxDOT districts. The Project Summary Report 0-4150-S – 1 – researchers performed a number of agencies. This information was used contribute to the development of tasks to identify effective pavement to develop recommendations for the the handbook. The handbook was marking practices for sealcoat and selection of marking materials on developed to provide a single source hot-mix asphalt concrete (HMAC) concrete pavements. of information for anyone involved roadways in Texas. The researchers with pavement markings in Texas. reviewed literature, identified current Measuring Pavement TxDOT and alternative pavement Marking Thickness marking practices, and evaluated What We Found … various pavement marking treatments Pavement marking thickness is The researchers identified numerous in the field. The pavement marking one of the two primary inspection findings that can have an impact on field evaluations were performed measurements made with pavement the quality of pavement markings and on surface treatment and HMAC markings, the other being the resulting effectiveness of those roadways. In most of these field retroreflectivity. Researchers compared markings. evaluations, researchers measured the relative accuracies of thermoplastic thickness measurement with caliper the retroreflectivity of newly applied Pavement Marking Conferences pavement markings and monitored the (common field practice) versus The findings from these conferences performance of the markings over time. needlepoint micrometer (recommended provided the researchers and TxDOT In total, researchers made more than field practice). The main difference staff with much useful information. 9000 retroreflectivity measurements between the two measurement devices Research report 0-4150-3, A at 18 different sites. Figure 1 presents is that the needlepoint micrometer is Summary of Two Pavement Marking a comparison of white edgeline capable of measurement between the Conferences for the Texas Department retroreflectivity over time for various beads, while the caliper is capable of of Transportation, summarizes the marking thicknesses. measuring only to the top-of-bead. The difference between the two activities and findings from the devices is significant because TxDOT conferences. Significant suggestions Markings for Concrete Pavements specifications require contractors to resulting from the conferences include: Several TxDOT districts have achieve minimum thermoplastic binder • Use 100 mil thermoplastic for all experienced difficulties getting the thickness, not including drop-on beads. standard TxDOT thermoplastic marking longlines on new sealcoat. material to provide adequate durability Pavement Marking Handbook • Experiment with concrete-specific on concrete pavements. In some thermoplastic materials and two- districts, thermoplastic markings have Developing the TxDOT Pavement component materials (e.g., epoxy) an expected life span of a year or less Marking Handbook was the major on concrete pavements. due to de-bonding between the marking implementation effort of the project. Using the information gained from the • Establish consistent statewide and pavement surface. To address these striping inspection practices. items, the researchers synthesized other four activities, TTI researchers information from a number of sources, developed the handbook and refined the • Establish a single statewide including National Transportation content based on input from a panel of retroreflectivity performance Product Evaluation Program (NTPEP) TxDOT staff and selected contractors specification. data and other state transportation that met on several occasions to Figure 1. Average Retroreflectivity for White Edgeline. Project Summary Report 0-4150-S – 2 – • Warranty specifications should Measuring Pavement be limited to use only on selected Marking Thickness contracts at the local level. Forty-seven thermoplastic • Monitor marking retroreflectivity pavement marking samples of on a number of different roadway varying thickness and beads were types to determine reasonable taken from striping jobsites statewide retroreflectivity values and and used in the analysis. Research performance periods. report 4150-1, Analysis of TxDOT • Until more experience is obtained, Thickness Measurement Procedures use 250 mcd/m2/lux white and Figure 2. Locations for Measuring for Thermoplastic Pavement Markings, 175 mcd/m2/lux yellow for Marking Thickness. summarizes the findings from the minimum retroreflectivity analysis. The results show that the performance of new markings. • To obtain a more accurate caliper measured an average of representation of long-term 20.5 mil and 16.7 mil thicker than Markings for Flexible Pavements pavement marking performance, the needlepoint micrometer for large The researchers identified few measure retroreflectivity at least one (Type III) and small (Type II) bead shortcomings related to pavement month after striping. samples, respectively. Based on marking practices on HMAC pavement the research findings, the following • To ensure adequate retroreflectivity recommendations were made: surfaces. However, for surface for both directions of traffic, treatments, numerous opportunities for measure retroreflectivity for • Thickness measurements should be improving pavement marking quality centerlines of undivided two-way made with a needlenose micrometer were identified. Research report roadways in both directions. to the top of the thermoplastic. 0-4150-4, Effective Pavement Marking • The use of a caliper to measure Practices for Sealcoat and Hot-Mix Markings for Concrete Pavements thermoplastic thickness is Asphalt Pavements, summarizes discouraged. the results of the evaluations. Based The researchers gathered much on the research findings, numerous useful information regarding pavement • A minimum of three measurements recommendations were developed, marking practices for concrete should be taken. pavements. Research report 4150-2, which include: • The most accurate measurement Effective Pavement Marking Materials method is to measure diagonally • Apply thermoplastic at a minimum and Applications for Portland Cement across the sample (taking at least thickness of 100 mil for all Concrete Roadways, summarizes three measurements per sample). longitudinal pavement markings the findings and recommendations Figure 2 illustrates where the on new surface treatments when no associated with this effort. Based on measurements should be made other durable marking exists. findings, the researchers generated on the sample. • Apply thermoplastic at a maximum a number of recommendations for thickness of 90 mil for all pavement markings on concrete longitudinal pavement markings roadways in Texas, which include: The Researchers on HMAC when no other durable • Use epoxy materials for long-term marking exists. Recommend … applications under the