Transportation & Mapping Solutions
Retroreflectivity of Pavement
CURRENT METHODS FOR MEASURING PAVEMENT MARKINGS AND INHERENT DRAWBACKS
The measurement of pavement marking retroreflectivity makes use of devices that are somewhat less susceptible to errors than those available for signs. See Facet Technology Corporation's Signs website. In 1992, the Manual on Uniform Traffic Control Devices (MUTCD) set minimum requirements for the retroreflectivity of pavement markings (RL). To view the most recent version of the MUTCD follow (L1). The standardized RL 30 meter geometry was later created by the European Committee for Normalization and the American Society for Testing and Materials (ASTM) in order to provide agencies with a common guideline for performing RL measurements. See Figure 1. Currently, several devices exist that have lasers and associated sensors that are set to the standard RL geometry.
There are two approaches for measuring RL. In the first approach, a hand-held RL retroreflectometer is placed directly
on the roadway for stationary measurements. See Figure 2. The second approach uses a mobile RL retroreflectometer, which is mounted to the side of a moving vehicle for on-the-fly measurements. See Figure 3.
Hand-held RL retroreflectometers suffer from multiple drawbacks which include:
- When a large number of RL measurements are needed, the process proves to be inconvenient.
- Lane closures are usually necessary when measuring RL on high traffic roads.
- The hand-held devices require personnel to stop at a pavement marking, place the device on the roadway, and make the RL measurement. If frequent measurements are made, the process becomes time consuming and expensive.
The operators of the device are exposed to traffic which often times results in injuries.
- Although hand-held RL retroreflectometers are initially less expensive, they are not as cost-effective as mobile RL retroreflectometers.
Mobile RL retroreflectometers, such as the Laserlux built by the RoadwareCorporation, suffer from multiple drawbacks which include:
- The vehicle-mounted sensors suffer accuracy problems not seen with the hand-held devices. The driver of a vehicle with a mounted sensor must direct the vehicle such that the sensor remains above the pavement markings to be measured.
- Drivers must be highly trained in order to perform the procedure.
- In addition to the near-impossible requirements placed on the driver, the vehicle-mounted laser sensors can only measure pavement markings that are in its direct path. Thus, the measurement of RL across the entire width of the roadway requires many sensors or, as is usually the case, will leave many pavement markings unmeasured.
With such a large amount of pavement markings that must be measured, an automated RL data collection system is needed that addresses the shortcomings of the existing techniques for determining RL. More automation will enable higher throughput, which is a necessity for the widespread utilization of the RL measurement systems. The next section will focus on how Facet Technology Corporation's RetroView™ methodology will forever change the retroreflectivity industry.
BENEFITS OF FACET TECHNOLOGY CORPORATION'S METHODOLOGY
As discussed in the previous section, current methods of measuring RL are inconvenient, unsafe, inaccurate or they provide insufficient coverage. Facet Technology Corporation's multi-wavelength, active sensor measurement system is an integral part of the state-of-the-art RetroView™ data collection vehicles. Since RetroView™ vehicles use a multi-wavelength energy source, they don’t suffer from the same limitations as the laser-based systems.
RetroView™ vehicles will allow accurate RL measurements to be gathered across the entire width of the roadway while traveling at normal traffic speeds. This results in better coverage of the pavement markings without disrupting the flow of traffic or wasting valuable time. Accuracy and ease of use are the cornerstones of our RL approach.
Once the information is gathered, our innovative graphical display tool (RetroView™) can be used for planning and maintenance purposes. Additionally, RA (traffic sign retroreflectivity) and RL can be determined from the same raw data set. This combined utilization makes for efficiencies never seen before in transportation management.
Our combination of ease of use, greater accuracy, and innovative graphical planning tools make the RetroView™ approach to retroreflectivity a methodology that can be deployed on a broad scale. For a more technical overview of Facet Technology Corporation's approach, see (L2).
