U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: Date: March/April 1999|
Issue No: Vol. 62 No. 5
Date: March/April 1999
What is the public's top priority for the highway system?
A couple of years ago, the Federal Highway Administration (FHWA), working with several other highway industry organizations, funded a national highway-user survey to answer that question. The survey was taken to help determine a direction for improving the quality of the nation's highway system.
The May 1996 report that came from the National Quality Initiative Highway User Study stated, "It is clear that the top priority for improving the nation's highways is to focus on the quality of the roadway surface. This is the factor that will most significantly increase public satisfaction with the highway system."
To the average motorist, a smoother ride means a lot of things. The first thing drivers notice is that there is a lot less noise from a smooth pavement surface. After a long trip on good highways, motorists realize that they're not as tired from the constant vibration of rougher roadways, and they know logically that there's been less "wear and tear" on the vehicle, especially its suspension system.
With the results of the highway-user survey in mind, pavement specialists in FHWA saw great potential in Arizona's approach to smoother highways. This might be the ideal way of answering customer demand for a better ride. The two agencies are now working together to encourage other state departments of transportation to use that approach.
New and replacement highways being built in the Grand Canyon State under a new construction concept are 27 percent smoother than their predecessors.
That's not all. A side bonus is that these smoother roads will last longer, meaning the state spends fewer hours on maintenance and less money on upkeep. Typical highways last around 20 years, and projections on the new, smoother Arizona roads say they should last at least 10 percent longer. That also translates to less time that motorists will have to spend driving through construction zones.
The Arizona Approach
So what's the magic behind this new, smoother roadway? A new recipe for mixing asphalt? New, high-tech machinery?
Surprisingly, while such things do play a role, the key is remarkably simple: Set a standard for smoothness on new highways, and then make it worth the extra care and effort for contractors to reach that standard.
Determining standards has been difficult, and highway engineers have spent decades creating tools to measure smoothness. When the interstate highways were first being built, smoothness was measured by simply laying a straightedge across the road surface. Typically, this was a long board.
Such an approach is limited to measuring changes in the roadway's smoothness only within that span. Larger variations, such as every five or six meters, may not be picked up by the straightedge, but they could be felt by the driver of a car traveling at the standard speed limit of about 90 kilometers per hour.
To overcome the limitations of a short straightedge and to better measure the roughness the motorist feels, devices with names like profilometer and profilograph were developed. These provided marked improvement in measurement accuracy.
Arizona studied a variety of devices and settled on the profilometer, a unit connected to a computer mounted inside a cargo van. Measurements can be taken with the profilometer at highway speed. Using this device, engineers at the Arizona Department of Transportation (ADOT) found that the average smoothness level of newly paved highways was about 585 millimeters per kilometer (38 inches per mile). That is, the total variation measured in the average kilometer was 585 millimeters.
Once the average level of smoothness for new projects was determined, the engineers could set a goal for construction contractors to meet and encourage them to attain it.
However, reaching those levels would require extra effort on the part of the construction contractors and, perhaps, purchasing more accurate paving equipment. People in business for a profit aren't likely to make that effort without a monetary incentive. So, ADOT incorporated into their contracts a specification that would set a goal for smoothness and then pay the contractors extra money — above the contract amount — for attaining or surpassing that goal. The smoother the highway, the more incentive money the contractor could get.
So, Arizona has smoother roads, but at what cost?
"It may surprise some people to find out that we haven't lost money on the smoothness specification," said assistant state engineer Ron Williams. "The fact is, we've run about even with our construction cost estimates. The reason is that, while we've had contractors earn several hundred thousand dollars under it, once they see how they can lower their up-front bids by anticipating the money they'll get on the incentive, they reduce their bid prices accordingly."
Thus, the new, smoother, longer-lasting highways are costing the citizens of Arizona — who ultimately pay the tab — virtually the same as their earlier, rougher pavements.
Others state highway agencies have tried incentives with mixed results. One problem is finding the balance — an incentive amount that's large enough to make it appealing to the contractor and yet, not so large that the agency would lose a lot of money. Another challenge is dealing with the perception that a state agency is "giving away" money.
Because of a lack of experience with such things, many government agencies frown on such approaches unless the benefits to the public can be demonstrated. And that's exactly what ADOT did.
"[The state attorney general's office] told us they had five key areas that needed to be addressed. If we could answer those to their satisfaction, we could develop our incentive program," Williams said.
The five requirements were:
ADOT was disappointed at the small improvement in smoothness with their first effort in developing the specification. With the formula that ADOT developed, the incentive was not big enough to encourage contractors to go beyond standard paving practices. So, a second-generation specification was developed.
"We started meeting with the industry — our contractors, along with the Associated General Contractors and the Arizona Rock Products Association," said Williams. Together, the organizations worked on an approach that would stimulate more innovation from contractors.
"ADOT asked three or four contractors that were involved in the initial incentive work and [that] tried to come up with a fair, equitable spec where [ADOT] could benefit from the smoothness and the contractor could afford to take some risks and go forward with some new technology," said Matt Gully, a vice president of FNF Construction Inc. of Tempe.
The group came up with a specification that had the same level of disincentive — a penalty to contractors for not meeting the minimum smoothness level — as before; however, the incentive side of the formula would be two-and-a-half times larger than before. The result was that contractors quickly began working harder to earn incentives.
Coordination and Communication Are Keys
Paving crews working under a smoothness specification — especially those working under one for the first time — often have pre-paving meetings to make sure everyone knows his or her assignment and how much incentive is at stake. Setting the right frame of mind can help workers focus not simply on constructing a highway but on building a pavement worthy of pride and a bonus. And when the work gets underway, crew members are encouraged to keep communication levels high.
Bill Brown, a foreman for FNF, said, "We feel that if everyone on the crew understands everybody's function on the crew, then they are able to spot a mistake. Or, if we run into any problems, it's just a small switch [in personnel], and everything just falls into place."
The philosophy that successful contractors try to instill in their crews is that the overall paving process should be a continuous, deliberate, coordinated process rather than a series of independent jobs. This consistency has to start at the hot-mix plant, where the asphalt material is first created.
"Mix temperature plays a very important part in rideability," said Brown. "We try to keep our mix temperatures consistent all the time because a cold mix will definitely give you a variation in your mat thickness."
It can be a real challenge for contractors on large projects to get the right amount of paving material — all of it at the same temperature and consistency to ensure smooth paving — to the job site at all times. For some projects, the hot-mix plant can be many miles from the job site, and distance complicates efforts to keep the entire project coordinated. Simple things like traffic congestion between the plant and job site can throw the entire process out of whack. ADOT often brings the state highway patrol into the process at the pre-construction stage so that the patrol can assist in keeping the delivery trucks on time.
Many of the contractors' techniques for attaining a high smoothness level are tied to operation of the paving equipment itself. A primary method of controlling smoothness is by maintaining a non-stop paving process.
Traditionally, material is delivered to the hopper, which feeds the section of the paver called the screed, which lays down the new pavement. The paver is operated until the hopper is empty. Then, the operator stops the machine and waits until another load of material is brought in. But even when the hopper is empty, a certain amount of unused paving material remains just ahead of the screed. When the hopper is full again, the operator starts the machine to continue placing more asphalt concrete. The problem with this start-and-stop process is that it allows that excess material in front of the screed to cool. The screed then rides up over this cooler material, causing a "bump" in the otherwise smooth surface.
Paver operators have found that by running at a speed that matches mix delivery, so that new loads of material are dumped in before the hopper runs out, they never have to stop their machines. Thus, the material that's laid down is one continuous "pull" rather than a series of smaller ones. And surprisingly, experience has shown that at the end of the day, the slow-but-steady method lays down the same amount of asphalt as the stop-and-start method.
The Arizona contractors also have found that they must be more "protective" of the pavers' operation. Hauling units must not bump the paver when material is being delivered to the hoppers. ADOT contractors use belly dump trucks for mainline paving, and mix transfer devices, which are smaller vehicles that serve as middle men between the large delivery trucks and the pavers, can also be used.
Most paving machines have automatic grade controls that adjust the level of material being laid down. The sensors for these devices take their grade measurements from "skis" that provide a reference as they glide over the surface being paved.
Traditionally, skis are placed on the old, existing pavement surface, and the new pavement matches the smoothness of the old surface. That's fine if the old surface is very smooth. More typically, the old roadway has cracks and bumps or settlements, and the sensors transmit those flaws to the new mat.
Arizona contractors are trying different approaches, taking their readings off the new mat behind the paving machine or off the new milled trench ahead of the paver.
They've found another enhancement of the skis too. Much like the three-meter straightedge used by engineers could miss larger variations in smoothness, a short reference length between the skis can also miss some variation. Increasing the reference length by placing their skis farther apart produced more accurate measurements. By placing the front ski far in front of the paver and using a truss to extend the rear ski far to the rear on the new mat, contractors have been able to get a combined reference length of about 18 meters. This length makes for an extremely accurate measurement.
"I was surprised to see our guys had developed their own ski," said Gully. "Basically, they took a 20-foot [6-meter] inboard ski and ran a 30-foot [9-meter] rear ski with a reference wire between them. Within a couple of jobs, they had it fine-tuned. There are skis on the market that are similar to it, but basically, we developed our own ski system on the job."
The secret is to place the rear skis on the new mat using steel or pneumatic tires or shoes and to place the front ski inboard in the trench or on the previously placed overlay. The old mat should be avoided, whenever possible, as a reference source.
The Importance of Rollers
Once the new pavement has been placed on the surface, it must be compacted with rollers. Compaction is critical to reducing the permeability of the mat to give it greater fatigue life. Roller operators have found that they, too, need to be cautious in their work. If they happen to roll off the new mat just a little and the rollers touch even a small bump on the roadway edge, that bump is transferred across the roller to the inboard side, and the bump is mirrored into the new surface.
"On our first job, we kept getting bumps on our mat, and we couldn't figure out what it was. We marked every time the machine stopped, every time we dumped a truck, every time a roller pulled off the mat. And what we found out after about four or five days was that every time there's a crack on the existing shoulder, it was transferred onto our mat because our roller [operator] was hitting two or three inches [50 or 75 millimeters] of it every time he was pinching the edge down. And that little bump was transferring onto our mat," Gully said.
Rollers have to be operated according to accepted practice and never parked on the mat. With the paver moving at a slower speed, the rollers can easily keep up and compaction is improved.
An Opportunity for Smoothness
Matt Gully describes each phase of the highway construction process as an opportunity to get the surface smoother: "For instance, milling is one opportunity. A lift of paving is a second opportunity. Another lift of paving would be a third opportunity. So we count the number of opportunities, thinking we can improve the mat a certain percentage with each opportunity."
Many contractors support the ADOT model. In a presentation to the 500 asphalt contractors attending the Sixth Annual United States Hot Mix Asphalt Conference in Portland, Ore., in November 1998, Don Popejoy of Ritchie Paving in Wichita, Kan., called for a uniform national roughness criteria "so when we come together and talk about smoothness we have a common language." He emphasized avoiding "the two bid don'ts: don't stop the paver and don't bump the paver." He said government agencies must recognize that quality costs time and money and that incentives are appropriate.
"Contractors would respond to rewards for increases in smoothness above minimum quality level. Nothing motivates a contractor like a bonus," Popejoy said.
Three years ago, the highway industry asked its customer, the motoring public, what it wanted. The public's response was loud and clear. The pavement smoothness specification pioneered by ADOT has the potential to be a tremendous tool to meet that need. While it's no magic bullet, a smoothness specification with a worthwhile incentive can be an important step to get smoother pavement. And that's something everybody wants.
For more information, contact Joe Massucco at (415)744-2660.
Joe Massucco is a pavement and materials engineer in FHWA's Western Resource Center in San Francisco. His projects involve highway pavement design, management systems and construction, and highway materials. He currently serves on FHWA's Binder Expert Task Group and Superpave Technical Working Group. He has 30 years of experience in FHWA, serving in the Federal Lands Office and Region 9. His bachelor's and master's degrees were awarded by the University of Arizona.
John Cagle is the marketing specialist in FHWA's Western Resource Center in San Francisco. He has 26 years of experience in all aspects of marketing, including market research, public relations, and advertising. He is accredited in public relations by the Public Relations Society of America (PRSA). His experience includes working for major consumer-products corporations, a market research company, consulting engineering firms, and state and federal transportation agencies. He has taught classes on marketing at community colleges and major universities, and he has received awards from PRSA, the International Association of Business Communicators, the Texas Public Relations Association, the WorldFest Charleston International Film and Video Festival, the National Association of Government Communicators, and the American Association of State Highway and Transportation Officials. He is a member of PRSA and the American Marketing Association.