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    PAVEMENT CONDITION INDEX
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By using pavement preservation treatments such as micro surfacing (shown here), in conjunction with mill-and-fill cycles, agencies can save up to $500,000 per two-lane mile over a 50-year period when compared to mill-and-fill-only programs. To most effectively stretch the budget, target up to 40% of paving dollars to preservation. Photo: ISSA

Government agencies are fighting more today than ever to get the most out of their shrinking road budgets. The options are pretty clear, especially now that the word has been out for long enough about pavement preservation.

Most agencies know pavement preservation techniques such as slurry and micro surfacing, chip sealing, and crack treatment can extend their budgets. In fact, agencies worldwide are saving millions each year and preserving hundreds of extra lane-miles by choosing pavement preservation. Now, with budgets that have been stripped bare, pavement preservation is starting to clearly justify its benefits to agencies and residents using the roads.

Pavement Condition Index

The International Slurry Surfacing Association (ISSA) has applied a hypothetical cost scenario to the Pavement Condition Index chart developed by the Army Corps of Engineers. In the example chart on this page, a road that receives three preservation treatments over a 25-year period at $2/square yard will remain in good condition for a total cost of $6/square yard.

If the road is left untreated for 11 years and pavement preservation is used as reactive maintenance to preserve the pavement, the cost will be approximately $4/square yard. Waiting this long to apply a treatment generally leads to a deteriorated road base structure, so the reactive maintenance treatment will only last about four years, when it will require yet another treatment or rehabilitation. In comparison, if nothing is done for 12 or more years, a mill-and-fill (mill and overlay) or full rehabilitation will be required at a cost upwards of $12 to $16/square yard.

“In the past, these pavement preservation tools were often put on roads that were too far gone for them to do any good, and the result was that the pavement failed quickly,” says Phil Tarsovich, president of Glen Allen, Va.-based contractors Slurry Pavers, Inc. “But I think we're finally getting over that. Agencies are educated now, and in general, they know that pavement preservation works when you get the right treatment on the right road at the right time.”

The Pavement Condition Index, developed by the U.S. Army Corps of Engineers, is generally accepted as the industry standard for scoring pavement condition (see “Pavement Condition Index” on this page). It provides a rational basis, calculating deterioration rate and deterioration modeling. The data can be used in conjunction with a pavement management program to develop a plan for pavement preservation, pro-active maintenance, and rehabilitation. Agency engineers can survey pavements for cracks and deficiencies as identified in the Federal Highway Administration's Pavement Distress Identification Manual, then assess their score to evaluate which roads to focus on first.

Real-world proof

“We started using micro surfacing in the late 1990s. We saw success with it, and we're at a point in our program that we're very comfortable with it and feel it's a lasting tool for us,” says Jay Norris, special projects engineer for Tennessee DOT (TDOT). Norris says that TDOT also uses chip seal, crack treatment, shoulder sealing, and single-joint stabilization as part of its preservation program.

The agency's Chief Engineer, Paul Degges, began to devote 10% of TDOT's $100 million state route budget to pavement preservation processes in 2007. In that first year, the department rehabilitated 900 of the state's 1,500 state highway lane-miles with asphalt paving; the other 600 miles received preservation treatments. “We treated 40% of our total lane-miles using just 10% of the budget. We saw a huge benefit in that,” Norris says.

If a lane-mile is approximately 7,040 square yards, and preservation treatment costs $2 to $3/square yard, the cost to preserve one lane-mile is between $14,000 and $21,000. TDOT was able to treat 600 lane-miles at a cost between $8.5 and $12.7 million. Rehabilitation costs between $12 and $16/square yard. The cost to rehabilitate one lane-mile is $85,000 to $113,000, bringing TDOT's cost to rehabilitate 900 lane miles to between $75 and $101 million each year.

TDOT treated 1,500 lane-miles total with preservation and rehabilitation applications. If the agency had ignored pavement preservation, and had instead devoted its annual state highway budget to rehabilitation, it would have only been able to treat an additional 100 lane-miles, for a total of 1,000 lane-miles for the year.

By consistently devoting money to pavement preservation each year, agencies are able to maintain four to five times the amount of lane-miles than they can if they only try to rehabilitate the worst roads.

“If you don't take care of your roads through pavement preservation, you'll have a lot of roads that are in good shape and a lot of roads that are in bad shape. There's no middle. Over time, that will hurt you,” says Norris. “Pavement preservation helps to move a lot of roads into the middle. Everything moves up to a fair-to-good condition that way. We want to keep as many roads as possible in good condition.”

Kent County, Mich., has used micro surfacing for more than 15 years. By the mid-2000s, which were peak years for the agency's budgets, the county devoted more of its budget to pavement preservation than to reactionary maintenance.

“We did it because we had the money,” says Jerry Byrne, director of maintenance and local construction. “Right now our budget is the same as it was in 1998, but the price of oil has gone up. Even though we're having to be more reactionary because of budget cuts and the price of oil, we still are trying to get in at least 30% pavement preservation. And, as our budget increases over time, we will go back to doing more preservation.”

Byrne says that while pavement preservation's budget-stretching abilities allowed the county to increase its use of the tool, it was the residents themselves that also directed the agency's decision. “We could cover more square yards of road for the money with micro surfacing than with anything else except chip seal, and residents were happier with micro surfacing,” he says, explaining that thin overlays like chip seal sometimes cause problems with manholes, drains, and driveways. “We get a nicer product for the money.”

Residents benefit from time savings, as well. A road can be open to traffic within an hour, and a project completed by the end of the day. For projects within subdivisions, Kent County devotes 80% of its budget to micro surfacing treatments.