Agenda - Public Works Committee - 05/21/2002

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PW CASE # A DISCUSSION OF DIRT VERSUS PAVED STREETS By: Steven J. Jankowski, City Engineer Introduction: Recently, there has been interest by the Committee in reviewing the few remaining dirt streets within the City. Specifically, the Committee directed that a comparison of the maintenance costs be provided. Two separate analysis approaches are provided within this case. Secondly, the Committee requested that a maintenance program that would provide an acceptable level of service on unpaved streets be investigated. This case also plans to meet that directive. Comparative Analysis of Dirt versus Paved Street: The following is a comparative analysis of the taxpayer expense associated with the maintenance costs over a thirty-year period. The analysis is based on a half-mile of roadway which might be typical of 156th and 157th Avenues between Variolite and Armstrong Boulevard. Attached are separate analysis showing the typical maintenance requirements for each type of street. In actual practice it is not unusual to deviate from this typical schedule for paved road maintenance. Similarly, dirt road maintenance is closely tied to the number of rainfall events which occur between March and November, which can also vary from year to year. The comparative financial analysis is based on two primary unit costs. The unit costs for seal coating and overlays are $0.85 per square yard, and $3.30 per square yard, respectively. These unit prices are the current costs, including both construction and project overhead, based on the City's experience with it's annual street maintenance program. The dirt street maintenance is based on the current charge rate for the use of the City's grader operation at $100 per hour. The results of the analysis show that over a period of thirty years, the total number of City dollars spent on dirt street maintenance is 88 percent of that projected for paved streets. However, since there is a significant difference in the cash flow expenditure between these processes, annual versus periodic, it is useful to also compare them using a present worth analysis. Present worth represents the amount of money that would be needed at the onset of the thirty-year period to pay all expenditures with the unspent balance earning interest at a specified rate. A zero balance would remain after the 30- year period. Based on a present worth analysis, dirt street maintenance is between 112% to 115% as costly as paved street maintenance, using 6% and 8% interest rates respectively. It should be pointed out that the idealized schedule provided for bituminous street maintenance has not always been realized because of budget limitations and pavement ratings.