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July/August 2010

Trafficking in Safety

The Standards of ASTM Committee E17

ASTM International Committee E17’s standards impact vehicle safety from the car you drive to the space shuttle through standards for the vehicle-pavement interface, traffic monitoring data and more.

Where the rubber meets the road — or runway — that’s where the work of an ASTM International technical committee makes the difference in safety. It’s an interface critical to the safety of people traveling highways. It’s an interface critical to an airplane’s safe takeoff and landing. And it’s an interface that has been the focus of an ASTM International committee for 50 years.

ASTM Committee E17 on Vehicle-Pavement Systems has developed standards to determine how smooth pavement surfaces are and how much grip a vehicle can capture on a curve or when stopping. Among the group’s time-honored and commonly used standards are methods to measure the skid resistance and the profile ride quality of a car on a road or a plane on a runway. More recently, Committee E17 has considered the need to collect, compare and archive data about traffic movement and has started to address the noise that is generated at the vehicle tire/pavement interface.

A good pavement-vehicle interface has great significance, according to E17 members. “It gives the traveling public, whether they be on highways or in airplanes operating on runways, a better margin of safety, particularly under adverse weather conditions,” says Thomas Yager, retired senior research engineer, National Aeronautics and Space Administration, Hampton, Va., and longtime ASTM member.

The Road-Tire Connection

The critical connection between vehicle tires and the road can be tested and better understood with the use of E17 standards. About this attribute, current E17 Chairman Kevin McGhee says, “The ability to characterize resistance to skidding in any direction is the most essential thing E17 does for safety.” McGhee is an associate principal scientist for the Virginia Department of Transportation, Charlottesville, Va., and an ASTM member since 1997.

Committee E17 defines skid resistance as “the ability of a traveled surface to prevent the loss of tire traction (E867),” and a core E17 document standardizes a familiar procedure to check it. ASTM E274, Test Method for Skid Resistance of Paved Surfaces Using a Full-Scale Tire, details how to measure pavement skid resistance using a locked wheel tester and a special test tire. “E274 is a standard that defines the operation of that skid trailer,” says Yager. “It’s a device that provides spot measurements of friction at constant speed.” The skid trailer includes a hose and nozzle that lays down a stream of water in front of a full scale rib (E501) or smooth (E524) tire specified by such performance characteristics as tensile strength, modulus, specific gravity and elongation.

Information about pavement friction from various testers together with surface texture measurements can then be compared using another E17 standard: E1960, Practice for Calculating International Friction Index of a Pavement Surface, which was developed in the PIARC (World Road Association) International Experiment to Compare and Harmonize Texture and Skid Resistance Measurements. Veteran ASTM and E17 member J.J. Henry, Huntingdon, Pa., who was involved in the PIARC work, says that the index was developed to harmonize devices that measure wet pavement friction. The index consists of parameters that report the calibrated wet friction and anticipated change in wet friction with speed, the speed constant of wet pavement friction.

The index allows highway professionals to compare roads internationally. “Whether a fixed slip tester in the United States, a locked wheel tester in Saudi Arabia or a scrim, a side force coefficient tester, in Germany, if we measure the texture in each location with the friction data then we can turn all of the numbers into the same index, the International Friction Index,” says Frank Holt, vice president of business development for Dynatest International, Westland, Mich., an E17 member and former E17 chairman. Comparisons of friction results can lead to better mix designs and reduced road maintenance costs.

The committee is also responsible for standards that characterize the roughness of a road, which makes a difference in the comfort of a ride and ultimately safety. “With a rough road, you can lose control,” says Holt, who adds that the World Bank, headquartered in Washington, D.C., uses roughness as a factor in decisions about funding pavement rehabilitation internationally. One E17 test to measure roughness is E1274, Test Method for Measuring Pavement Roughness Using a Profilograph, which calls for an articulated multi-wheeled device that records road bumps over a specified size. Another frequently referenced roughness standard is E950/E950M, which describes a standard approach for taking direct measurements of elevation profile, which can then be used to estimate roughness. E1364, Test Method for Measuring Road Roughness by Static Level Method, focuses on direct measurement of elevation profile and is typically used to validate other profile-based measurement methods. E17 also covers data format requirements (E2560) for the profile-based systems as well as guidance for measuring and reporting the International Roughness Index (E1926).

Checking Runways

As the U.S. space shuttles take their final flights this year, scientists and engineers will check and recheck the runways to measure friction and determine runway condition. The procedures are based on such E17 standards as E1859, Test Method for Friction Coefficient Measurements Between Tire and Pavement Using a Variable Slip Technique, which utilizes a series of friction force measurements of a braked test wheel as it is pulled over a pavement surface.

Runway friction tests are taken within 3-5 m of its center, going up one side and down the other, according to Yager, so that the equipment software produces three values representing each third of the runway. Pilots then know where rubber buildup exists due to previous landings. Yager says, “rubber buildup reduces the texture and hence the friction performance,” and pilots can plan landings according to the values from the ground vehicle friction measurements.

Continuous reading tests such as E2340, Test Method for Measuring the Skid Resistance of Pavements and Other Trafficked Surfaces Using a Continuous Reading, Fixed-Slip Technique, also provide a way to record skid resistance along a track length and determine averages for specific test segments.

The particular challenge of winter conditions — ice and snow — and their effects on runway friction, led to a multi-year collaborative project by Transport Canada, the U.S. Federal Aviation Administration, NASA and ASTM International called the Joint Winter Runway Friction Measurement Program. Numerous North American and European government and industry groups participated in the work, and thousands of tests using several types of equipment and procedures led to methodology to harmonize results. ASTM E2100, Practice for Calculating the International Runway Friction Index, provides a tool for airport operators and the aviation community to help evaluate runway conditions.

Henry says, “The use of different types of measuring equipment has caused confusion. This is particularly true in the reporting of runway conditions since the numbers from different devices used at airports do not have the same scale. The international runway friction index is an attempt to harmonize the reporting.”

For summer maintenance evaluations, airport operators can use E2666, Practice for Correlations of Mu Values of Continuous Friction Measurement Equipment to Determine Maintenance Levels for Use at Airports, which provides a unified friction level index to harmonize device output and thus better understanding by users.

Yager says that E2666 was simply another step in E17’s runway friction standards work. He adds that the FAA requested procedures for airport personnel operating various continuous friction measurement equipment to ensure that operators have the information needed for runway maintenance.

E17’s ongoing work on standards to be used by the air transport industry, government agencies and aviation organizations now focuses on WK5710, Guide for Friction Measurements of Aerodrome Runways, which outlines continuous measurement procedures used to assess runways that are new, resurfaced or surface treated and may or may not have rubber or weather-produced contaminants on them.

Traffic Information

A highway traffic engineer determines the traffic control at intersections such as the timing of traffic signals for safe and efficient movement of vehicles, and traffic studies are conducted for this purpose as well as for the design, planning and analysis of the highway system. E17’s Subcommittee E17.52 on Traffic Monitoring develops standards to aid the collection of high quality traffic information. For example, traffic engineers can now use ASTM E2667, Practice for Acquiring Intersection Turning Movement Traffic Data, to conduct traffic studies.

The ultimate purpose is safety and the efficient flow of vehicles. “A key use of traffic data is to measure the exposure or potential for traffic crashes. Accident analysis takes into consideration the traffic volume at a location, and crash rates measure the number of crashes per vehicle distance traveled,” says Ralph Gillmann, who leads the Highway System Performance Team, Office of Highway Policy Information, U.S. Federal Highway Administration, Washington, D.C. He adds that using such data can be used to improve transportation management and operations.

Highway officials can use ASTM E2300, Specification for Highway Traffic Monitoring Devices, to help choose equipment for their highway data collection needs. The standard provides performance requirements to help ensure that such sensors will do the job. This equipment uses a sensing element that converts, for example, a pulse on a pneumatic tube in the pavement into an electrical signal and uses electronics to amplify the signal. The signal then goes through processing to become data that counts vehicles on a particular road or records their speed, which lane they occupy and what turns they make.

A new standard now under development, WK25280, Practice for Highway Traffic Monitoring Truth-in-Data, takes the process another step to help manage field data collection through evaluation, acceptance, summarization and reporting to ensure consistency and transparency.

Another E17 subcommittee, E17.54 on Archived Data User Service, considers how to save and retrieve traffic data from intelligent transportation systems. The subcommittee provides guidance with three standards: E2259, Guide for Archiving and Retrieving ITS-Generated Data; E2468, Practice for Metadata to Support Archived Data Management Systems; and most recently, E2665, Specification for Archiving ITS-Generated Traffic Monitoring Data.

Highway Noise

The issue of highway vehicle tire/pavement noise is now under consideration in Committee E17, note Yager and McGhee, as it is becoming a higher priority in a number of U.S. communities, where more sound barriers have been constructed along roads to deflect noise from residential areas. McGhee notes that above 35 mph (56 km/h), the predominant noise source is the tire-pavement interaction. Groups are studying tire tread design and possible pavement mix changes to minimize noise levels, and Subcommittee E17.43 on Measurement and Evaluation of Pavement-Related Noise is taking the lead in E17 on standards for this area. A draft practice, WK26025, Practice for Measurement of Tire/Pavement Noise Using the On-Board Sound Intensity (OBSI) Method, will address the measurement of tire/pavement noise using the on-board sound intensity method, which uses a set of sophisticated tire-mounted microphones and a logarithm scale to mimic human hearing.

A Final Word

The diverse professional interests in Committee E17, which coordinates with other ASTM International groups such as Committees C01 on Cement, C09 on Concrete and Concrete Aggregates, D04 on Road and Paving Materials, and F09 on Tires, produce standards that are the foundation of methods used by government agencies, airports, the military, aircraft manufacturers, vehicle manufacturers, equipment manufacturers and consulting engineers. Holt says, “I have the unique opportunity to see a lot of the standards that we write in E17 in use around the world. ASTM standards are well respected because there’s a bunch of great users working hard to produce a quality standard.”

All those interested in participating in the work of Committee E17 are welcome. The committee next meets Dec. 5-8 in New Orleans, La. For more information, contact Daniel Smith, E17 staff manager, ASTM International (phone: 610-832-9727).