I-90 traverses the Cascade Mountains over Snoqualmie Pass, a harsh winter weather environment. I-90 also is the major truck transportation link to the Eastern U.S. These aggressive conditions make pavement marking problematic and successful performance scarce.
Recognizing recent improvements to pavement marking technology, the Washington State Department of Transportation (WSDOT) in cooperation with material manufacturers selected a variety of state-of-the-art materials and installation schemes to be evaluated under different weather and winter-maintenance conditions. Materials and methods that prove successful may be added to the WSDOT Standard Specifications and Standard Plans for future use in WSDOT contracts. Successful products also may be considered for future maintenance of I-90 as well as other state mountain passes.
Marked for work
Five sections of roadway were selected as listed in Table 1. Only white materials applied at a 4-in. width were tested. Manufacturers selected material application thickness and inset depth. The requested inset depth dimensions were subject to standardization by WSDOT.
Test Sections 1 and 5
These sections were primarily for spray-applied paint-like durable materials in a surface application. Each material was applied in a 0.2-mile section to one skip-lane line and to the right edge line.
Test Sections 2, 3 and 4
Durable material: Each durable material was applied in 5- to 10-ft skips in each section. The test skip-lane line was the one closest to the white edge line. The manufacturer also was invited to surface apply their material to the right edge line adjacent to their skip-lane line.
Paint-like durables: Each material was applied in a 0.2-mile length to one skip-lane line and the right edge line in each of the three test sections.
All Test Sections
Each paint-like durable was applied in all five test sections for a total application length of 1 mile of edge line and 1 mile of skip-lane line.
Waterborne paint applied by state crews was monitored as a control. The paint was surface applied. The crew retraced the lines during the time that the test material was being installed.
Into the groove
Because of the harsh environment it is unlikely that a surface-applied material will retain presence (durability) and retroreflectivity for several years. Paint-like durables were included to verify that they can provide one year of service. WSDOT plans to obtain several years of service from the inset grooves. The price of a 100-mil grind is incrementally more than a 60-mil grind, which several manufacturers requested and WSDOT considered as a minimum depth. Snowplowing and studded tires will wear the pavement surface down over several years, reducing the depth of the inset groove. WSDOT believes that it can refresh the lines for several more years in the deeper grooves (100 mil) for little extra cost.
Placing materials in a deeper groove should not significantly reduce retroreflectivity. The grade and super elevation of the road will provide drainage for the inset. Chains and studded tires will break up a thin layer of ice on the marking and sand in the groove. The wind generated by trucks also will help to blow out water and dry sand.
Products were generally placed in deeper insets as a result of the standardization. It is the opinion of WSDOT that the deeper inset will protect the marking better, benefiting the manufacturer and the motorist.
WSDOT chose to standardize on three inset depths and two widths:
- Liquid materials were applied in a 100 mil, 200 mil or 300 mil x 4-in.-wide insets dependent on material thickness. The groove depth was selected to place the top of the material below the pavement surface.
- Tapes were applied in a 100-mil-deep x 4.75-in.-wide inset. This width allowed for ease of straight tape application within the inset groove and improved tamping of the edges.
A summary of materials included in this project is listed in Table 2. All manufacturers used a double-drop bead system except as noted. State waterborne paint with a single drop of beads was tested as a control material. Material installation was accomplished during late September and early October 2004. Initial pavement marking retroreflectivity measurements were taken with a Delta LTL-X. Readings were taken on a representative sample of each marking material. Not all materials were measured at every section. Retroreflectivity results of the test sections were as follows:
Section 1: The retroreflectivity of most markings was in the 240-325 mcd-lx/m2 range with a high of 324 for the Polyurea C on the edge line, followed by readings of 323 for both the Methacrylate B and H lane line. The Methacrylate F lane line had the lowest reading with a 134.
Section 2: The retroreflectivity for most markings was over 200. Tape K had the highest reading at 874. Thermoplastic O had the highest reading for a site-manufactured marking at 347. Polyurea C edge line had the highest reading for the paint-like durables at 319. Tape J had the lowest reading of 95.
Section 3: All the materials showed wear. The paint-like durables were in the 100 to 150 range with a high of 156 for Polyurea C on the lane line. Most of the inlaid durables on the lane line were below 100. Two durables on the lane line were in the 100 to 150 range, the Thermoplastic N at 125 and the Thermoplastic P at 141. The Methacrylate H had the highest readings for the inlaid durable lane line materials at 221 and the highest reading of any edge line at 220 even though it was not inlaid.
Section 4: Most materials in this section were in the 150 to 250 range. The highest reading was 486 for the Tape K. The Methacrylate H obtained the highest reading for the site-manufactured marking at 276. The highest reading for the paint-like durables was 268 for the Polyurea C on the edge line. Section 5: The highest reading in Section 5 was for the Methacrylate H on the lane line at 356 and 270 for the Polyurea D. Polyurea D was installed with the air and pavement temperature at 32°F.
Table 3 is a section-by-section tally of the markings that meet three criteria: The failure number selected for this test, 100; the proposed minimum maintained retroreflectivity value of 125+/-; and the WSDOT Standard Specification acceptance level for new markings at 250.
As shown, 85% of the markings remain over the proposed minimum maintained retroreflectivity value of 125+/-. Over 40% of the markings retained the 250 value required for a WSDOT new pavement marking.
Durability ratings (10 high, 1 low) were based on ASTM Test Method D 913. This procedure compares the representative areas of the marking with a photographic reference standard to estimate the percent remaining. This test is done on a limited test area of 9 in. on either side of the center of the wheel track for a 4-in. transverse line in a test deck. It did present a challenge when evaluating a 0.2-mile section or five skips over 200 ft in which it was not possible to view the entire marking at once.
Sections 1, 2 and 4: Most of the materials showed wear but remained intact with a 10 rating. Polyurea C and D chipped on the inside of a corner in Section 2 where rumble strips were filled in and vehicles were “cutting the curve.”
Section 3: The paint-like durables had a rating of 7 to 9. Three durables had a rating of 10 (Methacrylate F, G and Thermoplastic P). Tape J was caught by snowplows and delaminated. Tape M received a rating of 5, with material worn and gray.
Section 5: Most of the materials were rated 9 or 10. The Methacrylate H on the edge line was scraped off by plows due to a shoulder drop-off. Even so, the retroreflectivity reading was much higher than state waterborne paint. The Polyurea D on the edge line experienced adherence problems and was rated a 5.
The following actions will be taken by WSDOT:
Methacrylate A, B: Pursue writing a specification to use this material application method on the surface and inlaid.
Polyurea C, D: Pursue writing a specification to use this material on the surface and inlaid. Add Polyurea D to Qualified Products List (QPL).
Modified Urethane E: WSDOT does not feel it needs two similar products, modified urethane and polyurea. The polyurea seems to perform better. The modified urethane will not be pursued.
Methacrylate F: This material had low retroreflectivity readings when new and throughout the test. It will require additional evaluation to ensure that the specified initial retroreflectivity requirement in the Standard Specifications is met. Methacrylate G: No action will be taken on this material.
Methacrylate H: Pursue writing a specification for this material application method on the surface and inlaid.
Tape I: This 60-mil-thick product is expected to meet the WSDOT long-line specification for Type C2 Plastic. This product had retroreflectivity readings of 163 and 157 in Sections 2 and 4, respectively, on April 20. It failed in Section 3 at the Dec. 16 reading.
Tape J: This 90-mil-thick product is currently on the QPL for transverse and symbol markings (only) statewide. The WSDOT long-line specification is for a 60-mil-thick material. This material did not perform well in the test as a long-line marking. The authors feel that if it were in a deeper inlay it may have performed similarly to Tape I with respect to retroreflectivity. There does not appear to be an advantage to installing a thicker material (more expensive) in a deeper inlay (more expensive) for the same performance. Tape J will remain on the QPL as a transverse and symbol marking (only) statewide. We will recommend that its status be changed from GFI to QPL status.
Tape K: This product, with standard adhesive, is currently on the QPL as a GFI product. The test tape has an improved pressure-sensitive adhesive. We will recommend that it be added to the QPL and that the status for the tape with standard adhesive be changed from GFI to QPL. The QPL will be rewritten to not allow this material in “ice chisel bit snow removal areas.” The vendor will not warrant the product in “mountainous, heavy snowfall areas above 5,000 ft.”
Tapes L, M: These tapes performed satisfactorily (retroreflectivity greater than 100) in Sections 2 and 4 and failed in Section 3. These materials are on the QPL as a “Removable Wet Reflective Preformed Tape.” They do not appear to be durable enough for long-term permanent applications. No change will be made for these products.
Thermoplastic N, O, P: These materials are currently on the QPL as GFI products. We will recommend that their status be changed from GFI to QPL status.
The products that have not failed will continue to be evaluated in March until failure. A project to improve the striping on I-90 over Snoqualmie Pass will be proposed based on the results of this test. The project will be subject to funding and the construction season.