August 18th, 2011
BLING FOR ROADSPreserve Infrastructure, by Catherine Higgins.
UDOT is looking for ways to improve the visibility of pavement markings at night during rain storms.
Small glass beads applied to paint make pavement markings shine at night. As vehicle headlights illuminate the road, each bead acts as a tiny retro-reflector that bounces light back to the source. Collectively, the beads make pavement markings highly visible for drivers. That is, until rain covers the road, creating a shiny surface that interferes with the retro-reflective quality of the beads.
Maintenance Planning Engineer Ken Berg and Region 2 Pavement Marking Coordinator Dan Betts are testing three different wet-night beads to see which one is the best retro-reflector. The test is a follow-up to work Betts has done to improve wet-night visibility and durability of pavement markings.
Betts’ method uses two different bead types – UDOT’s standard plain bead and a wet-reflective bead applied in equal proportion. Both are retro-reflective above and under water, but the wet-reflective bead is larger and has a “higher reflective index,” says Betts, making it better at reflecting light through water. Using two bead types “gives us the best of both worlds,” with good dry and wet retro-reflectivity.
To improve durability, the markings are placed in grooved pavement. Grooving the pavement slightly, about the thickness of a quarter, keeps the lane markings from being scraped off by snowplows and significantly improves life of the markings by six to eight times.
Soon, Berg and Betts will test three wet-reflective beads, all with different compositions, to see which one performs best during storms at night. Testing will be conducted on three contiguous 3500 foot sections on eastbound Bangerter Highway (SR 154) between Redwood Road and I-15. The close proximity of the test areas provides “a good comparison under similar if not exact conditions,” says Berg.
Pavement markings for the test were placed last week. On each test section, a different wet-night bead was applied in equal proportion with UDOT’s standard bead. All markings were applied on grooved pavement using the same method.
Next step: data collection
Both subjective and objective data will be collected. During storms, Berg or Betts will drive the sections, video tape and record field notes about any observable, subjective differences among the test sections. Collecting objective data is a two-person operation. A van with an attached retroreflectometer will be used to measure and quantify the reflectivity of the markings. Data sent to a lap-top inside the van will let testers see and compare measurements immediately.
The retroreflectometer measures by scanning across the marking, taking in some pavement on either side. A variety of information is produced, including a graph that provides a quick visual interpretation of the measurements. The software integrated with the retroreflectometer allows the user to choose from a variety of collection options. For example, upper and lower retro-reflectivity threshold values can be set for a pass-fail test.
By fall of this year, Berg and Betts expect to have preliminary results to share with others at UDOT and the larger transportation community. Testing will continue for two to three years, and the results will be used to select a cost effective safety improvement for road users.
More about UDOT’s pavement marking operations:
- The retroreflectometer measures light in millicandelas per lux per meter squared.
- Markings are applied using a double drop system that allows two types of beads to be dropped simultaneously on newly applied paint.
- For maintenance operations, UDOT uses water-based paint for pavement markings, which is 5 to 10 percent the cost of durable pavement markings, such as tape. Recessing the paint stripes below the surface of the pavement can help the markings last up to eight times longer than surface applied paint.
- UDOT Maintenance technitions can operate the pavement marking equipment, which saves time and conserves funding.