Pavement management justifies equitable fee for gravel hauling on Town of Plymouth roadways
Senior Project Manager
Vanasse Hangen Brustlin, Inc.
Member, APWA Engineering and Technology Committee
In addition to perhaps the most famous "Rock" in the United States, the Town of Plymouth, Massachusetts has significant gravel reserves within its boundaries. Sixteen gravel removal permits were issued by the Town between 1999 and 2003, totaling 4,378,226 cubic yards. It was estimated that these gravel removal operations would affect 23.81 miles of Town roadways. There was understandable concern over the potential for accelerated deterioration of the Town roadways affected by the gravel hauling.
The Town enlisted the assistance of a consultant with expertise in pavement management and engineering to estimate the level of pavement deterioration caused by the gravel hauling operations. The Town's goal was to establish a user fee that would be equal to the costs associated with road damage caused by the gravel hauling. It was anticipated that these fees, coupled with the Town's normal roadway maintenance and rehabilitation funds, would serve to maintain the public roadways in a safe, aesthetically pleasing and adequately performing condition. To assure that the Plymouth roadways are being maintained in an adequate manner, these fees will also serve to support increased administrative and maintenance costs related to the gravel truck routes.
Through meetings with the Town and the gravel operators, the haul routes used by each gravel area were identified. In early October of 2003, the town conducted detailed traffic counts on selected gravel hauling routes, and determined that the average daily traffic of 6,281 vehicles included 5.94% trucking of which 4.10% were gravel trucks from the permitted sites. In addition to the gravel haul routes, control segments were identified on which normal vehicular and truck traffic occurs. Where possible, segments of the gravel haul route roadways that do not carry significant traffic from the gravel sites were used as control segments.
The Town, with assistance from its pavement consultant, concentrated on applying pavement management technology to develop the estimate of an equitable gravel truck impact fee for the Town roads. This involved using the Town's existing pavement management database. Pavement condition data existed for every Town roadway within the community based upon an August 1999 pavement inventory and visual condition survey. Since many of the subject gravel excavation permits were issued near or after that time, an excellent record of factual pavement condition prior to the commencement of gravel hauling operations existed.
Pavement conditions were reevaluated on these routes as well as the control segments in 2003 in order to measure the deterioration in pavement condition on both the gravel truck routes and the control segments. This analysis revealed an estimated loss in service life between the gravel truck routes as compared to the normal road segments represented by the control segments.
The overall average loss in pavement condition for the selected gravel trucking routes was computed to be 0.56 PCI points per month. The overall average loss in pavement condition for the control segments, without the gravel trucks, was computed to be 0.14 PCI points per month, or a net damage loss of 0.42 PCI points per month due to gravel hauling. At this rate, the portion of deterioration over the 41-month study period that could be attributed to gravel hauling is 17.2 PCI points. The average PCI on the gravel truck hauling routes was 94.5 at the beginning of the study period. The deterioration due to gravel hauling would result in a PCI of 77.3.
It was determined that a nominal one-inch leveling course followed by a two-inch hot mix asphalt overlay and tack coat at a total cost of $4.75 per square yard would be required to return a road with a PCI of 77.3 back to a 94.5. The cost of rehabilitating the average haul road, calculated to be 1.81 miles long and 26.8 feet wide, was computed to be $135,178. Dividing this cost by the average of 585,959cy per gravel area yielded a cost of $0.23 per cubic yard to repair road damage related to gravel hauling.
In addition to the road rehabilitation costs estimated above, there was a recognition that the gravel hauling operations will result in increased administrative and maintenance costs to the Town. These include additional roadway sweeping and catch basin cleaning, more frequent pavement condition surveys on the gravel routes, and pavement design and quality assurance testing costs associated with the rehabilitation work. The cost of these activities was estimated to average $39,267 per permit area. Distributing this cost over the average of 585,959cy per area resulted in an additional assessed fee of $0.07/cy for the increased town administrative and maintenance costs. The total impact fee can be spread over the life of the permitted operation to determine the actual fee per cubic yard.
The condition of the Town's roadways will be tracked through the use of the Town's pavement management system and annual road program. In the future, the fee structure for gravel hauling on Town roads can be reviewed based on updated roadway condition information and pavement structure data that will be obtained. Many communities are successfully using pavement management systems to forecast future roadway funding needs, justify budget requests, and plan annual road programs. The Town of Plymouth recognized that data from its pavement management system could help determine the true impact of gravel hauling truck traffic on Town roadways, and serve as the basis for an equitable roadway user fee.
Gordon Daring can be reached at (860) 632-1500 or at firstname.lastname@example.org.
Editor's Note: The following publications are excellent resources in the area of pavement management: Pavement Management with MicroPAVER; Pavement Management for Airports, Roads and Parking Lots; PAVER: Pavement Condition Index Field Manual - Concrete; and PAVER: Pavement Condition Index Field Manual - Asphalt. All of these publications can be ordered online at www.apwa.net/bookstore or call the Member Services Hotline at (800) 848-APWA, ext. 3560.