Paving program efficiently upgrades city’s streets
Knoxville, Tenn., has an ongoing pavement management program that, to date, has enabled it to prioritize and resurface more than 450 miles of streets out of the approximately 1,000 miles of streets within city limits. The program, initiated in 1985, is administered by the city’ department of engineering and has several basic elements, including pavement testing, coordination with utilities, utility permits, complaint tracking, annual resurfacing contracts and quarterly reports to the city council.
Street testing, the most important part of the program, helps prioritize roads for future resurfacing. The city has hired Infrastructure Management Services, Arlington Heights, Ill., to assist in developing this information.
Testing is divided into two areas: detailed sub-surface investigation of the road and analysis of the pavement surface. A laser road surface tester is used to identify depressions, rutting, length and depth of cracks, potholes and utility cuts. The testing apparatus consists of a series of lasers mounted on the front and rear of a van to provide an eight-foot-wide continuous inventory of the street.
Sub-surface information is obtained using a Dynaflect, a device that uses vibratory and sonic principles to determine sub-surface strength. This information is compiled, and a rating is determined for sub-surface strength and surface condition. When combined, these ratings give an overall index rating for each street, ranging from one to 100 – the higher the rating, the better the overall condition of the street.
Actual testing is accomplished by dividing the city into six separate test sections, with all streets tested on a five-year cycle. By inputting traffic projections, the pavement management program can systematically “age” streets between test years so that all streets will be rated based on the current year’s rating. The program can predict future performance of streets so that, when choosing between equally rated streets, the city can prioritize the street deteriorating more quickly.
Utility cuts are one of the leading causes of deterioration of the city’s streets. To minimize the impact of these cuts, the city has implemented two measures, utility coordination and utility cut permits.
Utility cuts, especially transverse cuts, greatly affect the rideability of streets, so before resurfacing any street, the city contacts all potentially affected utilities to reduce the risk that newly paved streets will be cut.
Each year, prior to finalizing the streets to be placed in the resurfacing contract, a “utility list” is sent to all utilities for their review. If a utility is planning to upgrade its facilities or is prompted to upgrade facilities upon review of the list, it notifies the city. Those streets slated for utility upgrades are then bumped to a future resurfacing contract after the utility work is complete. This utility coordination helps to increase the time that a newly paved street is free of utility cuts.
Additionally, before doing any work within city rights-of-way, utilities must obtain permits from the department of engineering, which reviews the permits to ensure that all relocations or new installations are outside the limits of existing pavement. If the construction must be done within the pavement, an additional fee is paid by the utility.
Since all longitudinal cuts within the street pavement require a fee to cover the cost of resurfacing through the limits of the cut, utilities are encouraged to move outside pavement limits when possible. Fees collected from utilities are combined with funds appropriated for the annual resurfacing contract and used to resurface streets affected by utility cuts.
The cut permit process also notifies the city as to where utilities or their subcontractors will be working and enables the engineering department to inspect the work to ensure that proper techniques are used to backfill and pave the cut. Improperly backfilled utility cuts settle over time and cause very poor rideability of the roadway.
Street testing is supplemented with a complaint tracking system. Before final decisions on which streets should be paved, the city conducts a visual inspection of all streets recommended by testing for paving and all streets about which complaints have been received in the previous year.
Since it is not feasible to test entire street areas, on occasion the index rating of a street may not accurately reflect its condition. A visual inspection helps find those rare instances when the street index rating and actual conditions do not correspond.
As part of the pavement management program, a quarterly report is prepared to inform the city council of the current status of any ongoing construction contracts and/or planned contracts. Knoxville is divided into six separate council districts, and the total miles paved are to be equally divided among the six districts. The quarterly report keeps council members informed of the total miles paved in each district during each year’s resurfacing contract since 1988, and provides a detailed analysis of the streets that have been and will be paved.
The annual resurfacing contract is the final component of the program. The city currently is spending $2.1 million annually on resurfacing, enabling the engineering department to resurface approximately 40 miles of streets per year. A city inspector is on hand at all times during the construction process to ensure that all work is being performed in accordance with contract documents and specifications and to provide assistance when field conditions warrant changes to the contract.
Knoxville’s pavement management program enables the city to efficiently maintain its streets. Mayor Victor Ashe has identified better roads for Knoxville as a major goal, and coordination between the city and utilities has helped the department of engineering meet this goal.