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93 The objective of this research was to determine best practices for the safe, cost-effective, and environmentally acceptable removal of work zone and permanent pavement markings with minimal damage to the underlying pavement or visible character of the surface course. The objective itself had many areas that needed to be evaluated in order to determine the best practices for pavement marking removal. The summation of the conclusions and recommendations from this research effort are described in this chapter. The conclusions address information gathered during the research and how that infor- mation addresses the research objectives. The recommenda- tions provide guidance to practitioners by using the results of the research and the conclusions to establish best practices for pavement marking removal. Conclusions To address the objectives, the research team used a multi- faceted approach. The literature review, survey, controlled test deck removal, field observations, and additional research areas all yielded information used in forming the conclusions and recommendations of the research. Appendix E contains a standalone table of pros and cons of the most common forms of pavement marking removal. This table highlights the advan- tages and disadvantages of each removal technique, which should aid in the selection of the most appropriate removal technique. The survey responses indicated that grinding was the most common form of pavement marking removal and that it was preferred by many, even though most noted the drawbacks of pavement scars that are often left behind. Water blasting was also commonly used and is becoming more common as more equipment makes its way to the field. Water blasting was the most common method that the survey respondents would like to try. Both sand and shot blasting were commonly used, but they also both received several responses that indicated they were no longer being used. Outside of those four removal tech- niques, the temporary masking of markings was the only other method regularly used in the field. Other removal methods, such as chemical, heat, laser, and other forms of blasting, such as soda, dry ice, or glass, are not commonly being used. Grinding removal is the most available removal technique and is also the least expensive type of marking removal. Water blasting systems are becoming more common, but availability is limited in some areas. Water blasting is more expensive than grinding; the survey responses and literature review indicated water blasting can be, on average, 10 to 40 percent more expen- sive than grinding. The cost of removal is highly dependent on the availability of equipment and size of the removal con- tract. Typically, only grinding and water blasting are used for long stretches of removal because they can remove marking at a greater rate than other techniques. Other removal tech- niques, such as shot and sand blasting, as well as grinding and water blasting, are used for shorter removal sections. The environmental impact of pavement marking removal is something that should be considered when selecting a removal method. Removal can generate dust, limiting visibility for nearby drivers, or produce waste that may require special containment and disposal. Sweeping and vacuuming as well as wet removal are methods used to combat dust and collect the removal debris. Wet removal may be limited in colder weather due to the chance of freezing. State specifications indicate that 19 states require equipment to contain dust and debris espe- cially when conducting removal within 10 ft of an occupied lane. An additional 14 states require the prompt removal of dust and debris as the work progresses. Grinding equipment may or may not have a vacuum system that can capture dust and smaller debris. Grinding removal will require an additional pass from a vacuum truck or sweeper to remove the remaining material from the road surface. The new water blasting equip- ment has a high-powered vacuum system that is able to capture most of the removal debris and water, which results in no dust or the need for additional cleaning of the removed material. Sand blasting results in large amounts of debris from the sand C H A P T E R 7 Conclusions, Recommendations, and Suggested Research
94 and the removed markings and requires a vacuum truck or sweeper to remove the material from the road surface. The survey responses and literature review indicated that there are chemical removal systems that are environmentally acceptable, but these systems are seeing limited use. The use is limited because of dissatisfaction with previous removal results and length of time and costs necessary to remove the marking. Another possible limitation is that only paint pave- ment markings can be removed with chemical systems. There were no chemical removal systems found that have been used to remove any pavement marking type other than paint. There are methods of applying durable coatings over the markings to blend into the appearance of the pavement. The problem is that these coatings and the surrounding pave- ment may change colors at different rates over time, and the covered area will no longer blend as well as it did originally. The surface texture of the painted areas and the surround- ing pavement will also be different and may be noticeable under certain driving conditions, such as the sun being low on the horizon or the pavement being wet. Simply covering the markings with a durable material also leaves the possibil- ity that the marking may later be exposed and need to be either removed or recovered with another durable material. Subsequently, the MUTCD only allows the markings to be covered for temporary conditions. Color-matching paint sys- tems may be better suited in a light application over removed areas in the short term to help blend in color differences after removal until the removed area has time to age and blend into the surrounding pavement. Any materials placed over a marking to mask it need to be maintained so that the mark- ing does not become exposed over time. The literature review yielded research that evaluated the use of a sand seal across the entire lane width to mask the mark- ings. This technique was found to be effective at masking the markings while maintaining adequate surface friction. The cost of the sand seal was also much cheaper than removable black masking tape. This type of masking could be useful in certain situations but would need to be monitored to ensure that the covered markings do not begin to show through the masking material. The survey responses indicated that after the removal of pavement markings, fog or slurry seals have been used to help blend the removed areas with the surrounding pavement sur- face. The use of a fog seal or slurry seal to help blend color changes, scarring, or surface texture changes to the surround- ing pavement will only be useful on asphalt road surfaces. The researchers propose that on concrete surfaces where a discoloration occurred after marking removal, a larger area could be washed or cleaned with a high-pressure water blast- ing system to help blend in the removed area to the surround- ing pavement. The field studies indicated that when the sun is behind the viewer, it makes the removal area more visible by lighting up the unremoved marking and reflecting off the textured surface. When looking toward the sun, there is glare off smooth surfaces, and textured surfaces look dull. Using a technique such as a fog seal or water blasting a larger area will reduce visibility issues associated with the sun because the area will be more uniform in appearance. The survey responses did not indicate any usage of a combi- nation of heat and mechanical processes to remove markings. Several state DOTs indicated they have used a combination of grinding and blasting techniques, but not heat. The combination method some respondents typically use is grinding to remove the marking above the road surface and then a blasting method to remove the marking below the road surface. The thought is that the grinding can quickly remove the bulk of the material without damaging the road surface, and then the blasting can remove the rest of the marking quicker than it normally could because there is less material to remove. This results in a tech- nique that can remove all of the marking relatively quickly with minimal scarring. The field testing showed that this method can be effective, but there is still the opportunity for pavement dam- age if the blasting technique is too aggressive. This technique is also only effective for pavement marking materials that are thick enough for the grinding technique to be able to remove them without damaging the road surface. The MUTCD calls for removing or obliterating markings until they are unidentifiable as markings. There are not stan- dards for acceptable levels or criteria for how to determine a marking is no longer identifiable. The level of removal needed to make a marking no longer identifiable will differ for each situation. White markings on lighter-color road surfaces will not require the same level of removal as white markings on a dark surface. Removing a marking to the point of making the marking itself no longer identifiable may result in dam- age to the road surface that could be confusing to drivers. The MUTCD indicates that the removal of the marking should minimize pavement scarring. Again, there are not standards for acceptable levels or criteria for how to determine scar- ring. The wording in the MUTCD regarding how to mini- mize scarring acknowledges that when removing pavement markings, some scarring may occur. It is the agenciesâ job to ensure that appropriate pavement marking removal practices are used to minimize the scarring while removing enough of the marking material to no longer be considered as guidance or be confusing to drivers. In general, the state DOT specifications call for the com- plete removal of the markings while limiting damage to the road surface. Several states did call for specific levels of required removal, ranging from 75 to 100 percent, with the majority indicating 90 or 95 percent removal. Several states also indicted maximum allowable depth of pavement scarring rang- ing from Â¹â16 to Â¼ inch, with the majority indicating Â¹â8 of an inch or less. The survey responses did acknowledge the need for a balance between the removal percentage and damage to the road surface. The thought is that to attain 100 percent
95 removal, excessive damage to the road will occur, whereas 90 or 95 percent removal may do minimal damage to the road surface. Leaving marking material on the road surface or damaging the road surface will both be visible to drivers, so an adequate balance needs to be sought for each individual situa- tion. The required level of pavement marking removal should vary depending on the reason for the removal and the roadway conditions where the removal takes place. Based on current practice, typical removal should be specified at 90â95 percent, with Â¹â8 of an inch or less of pavement damage. The majority of survey respondents indicated that only sub- jective visual assessments were used to determine if marking removal was acceptable or not. While these assessments may be deemed acceptable, supplementing the assessment with quan- titative measures may be beneficial to help promote consis- tency between inspectors. Retroreflectivity measurements, scar depth measurements, and estimated texture depth measure- ments were found to be quantitative measures that could help supplement subjective assessment when trying to determine the quality of pavement marking removal. Retroreflectivity measurements will give an indication of nighttime retroreflec- tive contrast that drivers will see between the removed area and the surrounding pavement. Minimizing the retroreflective dif- ference between the removed area and the surrounding pave- ment will reduce confusion of the removed area at night. Scar depth and estimated texture depth measurements will provide a measure of damage to the road surface. Minimizing the scar depth reduces road surface damage and the likelihood the removed area will be confused as a marking, especially in wet conditions. Estimated texture depth measurements should be as close to the measurements on the surrounding road surface as possible, or in any lighting situation, the removed area and surrounding road surface will appear different. The controlled field test deck removal and field observations found many good and some bad pavement marking removal results. High-pressure water blasting provided good removal on the PCC surfaces with little damage to the road surface and good removal of the marking materials. On asphalt surfaces, the results were mixed. The system typically removed all of the marking, but in some test areas, the high-pressure water blasting system removed some of the surface asphalt and fines. The flailing truck had mixed results on both the PCC and asphalt surfaces. To achieve a high level of removal, the flailing truck typically left a scar on the road surface. Minimal scarring may be okay in some areas, but in critical areas such as lane-shift areas, scarring needs to be minimized as much as possible. The speed of removal depended on the marking type and the quality of the removal. The water blasting was as fast as or faster than the flailing for many of the tests. The orbital flailing system was not as aggressive as the full- size truck drum flailing system, and so it left minimal scarring on the road surface. The orbital flailing system did not dig into the road surface like the standard flailing systems did, result- ing in minimal changes to the surface texture and minimal scar depth. The drawback to this was the system seemed to have difficulty removing paint and preformed thermoplastic markings that found their way into voids below the pavement surface. The orbital flailing system was not a full-size system, which resulted in much slower removal than the other full-size removal methods tested. The combination removal had mixed results. On PCC, the removal was good, with removal results similar to those of the high-pressure water blasting alone, but at a higher rate of removal. On the asphalt surface, there was quite a bit of scarring of the road surface that was slightly worse than the removal using the high-pressure water blasting by itself. Care needs to be taken when doing the initial grinding of the marking above the road surface to not damage the road surface and to remove the marking as evenly as possible so that the water blasting can remove an even layer of the remaining material. Temporary tape is often used on final surfaces so that the material can be pulled up, unlike other materials that have to be removed by other removal techniques that are more likely to damage the road surface. Temporary tape is still not a perfect solution, as its removal may leave behind residue that may appear to look like a marking especially on PCC or light- colored surfaces. Further exploration of the NTPEP tempo- rary tape database would allow for more specific information to be evaluated that may be beneficial to a particular set of conditions. Users should evaluate the temporary tapes they want to use to select the most durable, the least discernible when removed, or a material that is the best combination of the two. In addition, other factors such as cost, color, and removability need to be taken into consideration. Recommendations The recommendations include factors to consider that relate to pavement marking removal and a set of best practices to assist in improving pavement marking removal quality. The standalone table of pros and cons of the most common forms of pavement marking removal in Appendix E should be used to help determine which type of pavement marking removal may be best suited for a given situation. The selection of a removal system needs to take into account many factors, each of which may be more or less influential on some projects. The proper consideration of each of these factors is the best way to achieve acceptable pavement mark- ing removal results. These factors include the following: â¢ What marking material is being removed? â¢ What road surface is the material on? â¢ How much of the material needs to be removed (what is the purpose of the removal)? â¢ Is speed of removal important?
96 â¢ What removal techniques are available and at what cost? â¢ Are there special environmental conditions that need to be considered? â¢ How long will the removed area be viewed by drivers (will a new surface be installed or markings restriped in the future)? â¢ Will the removed area be in a location where confusion could lead to an accident? â¢ Are there other measures that can be taken to minimize confusion to the driver? Best Practices Pavement marking removal should be specified as a percent- age of material removed based on the purpose of the removal. The percentage of material removed equates to the percent- age of the road surface made visible where the marking was removed. The purpose of the removal should also play a role in the removal method selected and other measures selected to pro- vide a roadway with delineation that is not confusing to drivers. Table 58 provides suggested percentage levels of pavement marking removal based on the purpose of the marking removal. These suggested percentages are based on the results of the sur- vey, literature review, and field evaluations. Based on current practice, damage to the road surface should be Â¹â8 of an inch or less while changing the road surface texture as little as possible. Changing pavement marking patterns is the most critical pavement marking removal because the old markings are no longer conveying the travel path to the drivers. Any errors in removal can lead to drivers being confused by the old mark- ings or the removed areas. A high percentage of the material needs to be removed, but damage to the road surface also needs to be considered. Open-graded or tined surfaces may require the material below the pavement surface to be removed with a blasting technique to minimize scarring. Depending on the road surface type and the road conditions, additional mea- sures may need to be taken to reduce driver confusion with the removed markings. These additional measures can include fog or slurry seals over the removed area or the entire lane width on asphalt surfaces. The friction of the road surface needs to be considered, but these techniques will help blend the removed areas with the surrounding pavement. On PCC surfaces, addi- tional light removal around the removed area or across the entire lane width can be conducted with a blasting technique such as water blasting to help blend in the removed area. Remove and replace is the process of removing the current pavement marking material and restriping in the same location where removal occurred. This type of removal is conducted to remove a poorly bonded material so the new material can form a good bond, to reduce the overall thickness of restriped markings, or to remove an aged marking that is incompatible with the new marking that is being applied. For remove and replace with compatible markings, the whole marking does not always need to be removed, so removal can be limited to at or above the road surface. This can help limit scarring to the road surface. Removal by grinding may be the best option, but if full removal or removal of material below the surface is needed, then water blasting or another blasting technique may be a better option to minimize scarring. When installing a new surface treatment or new surface overlay, it is advisable and sometimes required to remove the existing pavement markings. Pavement markings under a surface treatment or thin overlay may eventually become exposed as the new surface wears. Therefore, the majority of the material should be removed to ensure that the new sur- face does not eventually become exposed, and so that the new surface can bond well with the surface below it. The buildup of pavement markings under surface treatments may also be detrimental to the drainage of the road. Practitioners need to consider the work phasing and the final road surface. If markings are to be removed for a short duration prior to a new surface, then damage to the road sur- face is not as critical compared to a removed area that will be visible for a longer duration. Any removal on the final road surface needs to be accomplished with minimal damage to the road surface. It may be best to use temporary pavement markings on the final road surface until the final marking configuration so that removal will do as little damage to the road surface as possible. Purpose of Pavement Marking Removal Suggested Percentage of Material Removed Change marking patterns 90â95 (100 percent may be necessary in some instances) Remove and replace compatible materials 70â90 Follow new marking material manufacturer guidelines Remove and replace incompatible materials 80â100 Follow new marking material manufacturer guidelines Apply surface treatment or new surface overlay Follow state guidelines Table 58. Suggested percentage of pavement marking removal based on purpose of removal.
97 The selection of the most appropriate pavement marking removal system needs to consider the amount of removal that is required and the length of time available to complete the removal. If the removal quantity is large, full-size removal trucks should be used. If the removal quantity is small, hand units and the slower removal methods can be considered. The removal of symbols and text should be removed in a square or rectangular pattern so that the previous shape is not left as a scar or discoloration. This requires removal of the marking and the necessary removal/cleaning around the mark- ing to help blend in the area with the surrounding pavement by creating a larger removal area that is no longer recognized as a symbol or text. Older road surfaces that are experiencing cracking or sur- faces with joints may need special consideration when removal occurs. The use of high-pressure water blasting on these surfaces can lead to road damage if the water is allowed to penetrate into the cracks or joints. Grinding may also pose a threat to cracks and joints. Removal around these areas should be conducted carefully, such that the joints are not disturbed and the cracks are not made worse by the removal. Initially, any pavement marking removal project should begin with testing the removal equipment in a non-critical area to evaluate the removal. This initial testing will show how well the operators can use the equipment to remove the marking material and how much damage is done to the road surface. The test area can be used to adjust the equipment to find the ideal setup for the work required. If the operator and equip- ment cannot provide satisfactory results, another removal system should be considered. The quality of removal needs to be evaluated during the day, at night, and during wet conditions. Surface color changes and scarring will have a greater impact during the day than at night, whereas retroreflectivity from remaining marking material or retroreflectivity differences because of surface texture changes will be more noticeable at night. The direction of travel and the position of the sun also need to be considered. Wet conditions may fill pavement scarring, resulting in an area that looks like a wet marking and thus creating confusing delineation. Any areas with color, texture, or retroreflectivity issues should be corrected to reduce or eliminate driver confusion. Pavement marking specifications for areas where removal has occurred should consider post-removal conditions. Wider markings and continuous markings in transition areas will provide better guidance to drivers and may reduce confusion of the removed marking areas by enhancing the new mark- ings. Markings with high retroreflectivity levels should also be maintained in areas where previous removal could lead to confusion by drivers at night. The high retroreflectivity of the new markings will be more noticeable to drivers than removed areas of markings with lower retroreflectivity levels. Implementation This research report will serve as the primary means of trans- ferring the research results to practitioners. The report will be distributed directly to the survey respondents, as they have already shown interest in the research by participating in the survey and thus are the most likely candidates to be interested in implementing the results of the research. The report will also be distributed through the TRB E-Newsletter. In addition to this research report, the researchers intend to develop a paper to be submitted for presentation at the TRBâs Annual Meeting and for publication in the Transportation Research Record. A webi- nar on this research project, or pavement marking removal in general, may also be a good means of transferring these research results to those who can best implement them. Suggested Research The research described in this report used several quantita- tive and qualitative measures to evaluate the quality of pave- ment marking removal. What was not conducted was a human factor study to evaluate driversâ responses to visibility issues associated with pavement marking removal. A human factor study could evaluate the areas of pavement marking removal that are viewed as the most confusing by drivers and/or pro- vide additional information on developing required removal levels or how much change to the road surface is acceptable from a driverâs perspective. The survey of the current state of the practice indicated that chemical removal systems are not being used very often. Sev- eral possible reasons for this are dissatisfaction with removal results, length of time and costs necessary to remove the mark- ing, health and environmental concerns, and the limited mark- ing types that can be removed with current chemical removers. Near the conclusion of this research project, the research team was made aware of a new chemical removal system that claimed to be able to remove paint, epoxy, and urethane mark- ings while doing no damage to asphalt or PCC road surfaces and being environmentally safe. There was no time to evaluate this removal system, but if the claims are true, the chemical system may prove viable for the removal of applicable mark- ing systems in certain circumstances, such as lane-shift areas. The researchers suggest further research into recently devel- oped chemical removal systems to evaluate their claims and to determine if their use in the field by transportation agencies is feasible.