By James Careless
Pavement management systems (PMS) bring order to the world of roadway construction, maintenance and replacement. Such systems employ a mix of historical construction/material data, ongoing on-site road testing and specialized software to generate useful, reality-based information for government decision-makers.
“Today’s pavement management system is a computerized analysis tool that agencies use to evaluate different investment strategies so they can maximize performance within constrained funding levels,” said Katie Zimmerman, president of the civil engineering firm Applied Pavement Technology in Urbana, Illinois. “It enables agencies to determine how much money is needed to achieve different performance targets so decision makers have a realistic idea of what can be achieved.”
Having access to accurate PMS data helps ensure that the goals set for road maintenance by those in charge is in line with the money they allocate to these goals. “I’ve seen city councils and boards set targets indicating that 80 percent of their local roads should be in good condition without even knowing whether the available funding is adequate to meet that goal,” said Zimmerman. “Pavement management systems facilitate the type of analysis that’s needed to determine a realistic target for the expected funding levels.”
Making a difference in Washington
The Washington State Department of Transportation (WSDOT) has been using a pavement management system since the 1970s. “We started it out on a mainframe, migrated to a microcomputer, and today our pavement management system is web-based,” said David Luhr, WSDOT’s pavement management engineer. Thanks to the state’s efforts to retain and store road construction contracts and related information, “we’ve got a good idea what kinds of pavement we have where, and when/how it was built,” Luhr said. “We also do condition evaluations of our roadways on an annual basis, to keep our database up to date.”
Over the years, WSDOT has added capabilities to its pavement management system, with an eye to providing WSDOT managers and their political masters with meaningful, fact-based road condition information. “For instance, we can now evaluate the cost of road resurfacing on specific highways on an annual basis, using units of dollars per lane mile per year,” said Tim Rydholm, WSDOT’s pavement management system administrator. “This tells us how cost-effective each kind of available asphalt and concrete road treatment is over time; including how much it costs to maintain it.”
The result? Using its pavement management system, WSDOT is able to get more value out of its transportation budget dollars. In particular, having access to detailed PMS information allows road managers to extend the useful life and road quality through preventive maintenance and pavement rehabilitation, rather than letting highways deteriorate to the point of expensive replacement.
Tech trends in pavement management systems
The advent of computer technology has radically improved the detail and accuracy of road measurement technology that inform pavement management systems.
Many of these ‘tech tools’ are truck-based, such as the Rolling Wheel Deflectometer (RWD). Designed to detect asphalt highway ‘deflections’ (downward movement of the roadbed when weight is applied) as a measure of the roadway’s structural integrity and stiffness, the RWD allows such measurements to be taken at highway speeds. This eliminates the need to close lanes to regular traffic during roadway evaluations. “Data can be collected on 200 to 300 miles per day and can usually be done without additional traffic control vehicles,” noted the Federal Highway Administration’s (FHWA) website. “The data are used to provide a ‘structural map’ of an entire highway network and to target areas for detailed inspection and testing using a Falling Weight Deflectometer, coring or other static types of testing.”
For the record, the RWD is installed inside a specially designed tractor-trailer to apply known quantities of weight to the pavement below and to measure the pavement’s deflection responses. The tractor holds the RWD’s operator, laser controls, computer control and recording equipment. “Specially designed to control pitch and roll,” according to the FHWA website, the 53’ RWD trailer has a single rear axle loaded to 18,000 pounds. The measurement equipment includes four high-precision, downward-looking laser measuring devices mounted 8.5 feet apart. The rearmost laser is mounted between the rear wheels, just behind the centerline of the rear axle.
“The Rolling Wheel Deflectometer is an efficient tool for collecting road deflection information, quickly, accurately and over large stretches of road,” said Wayne Seiler; owner of the pavement evaluation, design, measurement and management firm All About Pavements in Mahomet, Illinois. “The data it collects is highly useful for both the structural and functional analysis of existing roadways and airport runways.”
A second advanced PMS tech tool, which WSDOT relies on, is mobile 3D surface imaging provided by Pathway Services of Tulsa, Oklahoma. Pathway uses a 3D camera system mounted at the back of a data-collecting van to capture a laser line projected behind the vehicle as it moves at speeds up to 70 mph. The laser line serves as a reference marker, against which the 3D camera system can determine height and rut (depression) variations in the roadway for both wheel paths; referenced against GPS locations recorded at the same time. The results are location-referenced high-resolution 3D and transverse images of the road; sufficiently precise to detect even the finest of surface cracks.
“This is a very advanced piece of PMS hardware,” said David Luhr. “It allows WSDOT to generate highly-meaningful road surveys, at a fraction of the time associated with human-based visual surveys.”
Also on the equipment side, “one trend that we’re noticing is the increased use of LiDAR to obtain additional road information such as bridge clearances,” said Zimmerman. Short for Light Detection And Ranging, mobile LiDAR systems are capable of measuring bridge clearance vertically and horizontally when the LiDAR measurement vehicle is moving at highway speeds.
The collected data “is then post-processed to extract mapping data, roadside asset feature data and various measurements,” according to the WSDOT research report ‘LiDAR for Data Efficiency.’ “The extracted data can be readily imported into a database for analysis accessible by all WSDOT business areas, thus reducing duplicate data collection and storage.”
The upside of pavement management system data is that it can help transportation departments make informed, cost-effective decisions; both in the short- and long-term. Such is the usefulness of this data, that federal funding is increasingly being tied to the availability of such information as well. It can justify the need for specific levels of requested project funding at the state and local levels, and allow the FHWA to assess how much bang they got for their buck afterwards from federal funding.
Another benefit is the opportunity for transportation agencies to gather all kinds of information at one time. “Data collection vans are being outfitted with everything needed to conduct a pavement condition survey while also collecting information on signs, lighting, guardrails, and other roadway appurtenances,” said Zimmerman. “It’s making agencies more efficient; ensuring that they get the data they need while streamlining their operations.”
The bottom line: Properly-managed pavement management systems are a boon to the transportation agencies who use them. “We could not do as much as we do with the money we have without our pavement management system,” said WSDOT’s David Luhr. “That’s just the way it is.”
Careless is a freelance writer based in Ontario.