Programs & Labs
Winter 2004
Finding the fountain of youth for snowplows
David Wyrick
All state departments of transportation face the problem of when to replace snowplows and other fleet assets. Determining an optimal time for fleet managers to replace these assets could save the DOTs a significant amount of money: replacing too early requires a great deal of capital and replacing too late results in extra maintenance and operations costs for the older trucks.
The current life-cycle standard is 12 years, but fleet managers are unsure of how this standard was established or if it is the best standard to follow. Furthermore, decisions about when to replace are often made based on the resources available for the year without planning for replacement ahead of time, resulting in a tendency to extend vehicle life rather than replacing on a regular basis.
In a recent research study, David Wyrick, professor and head of the Department of Mechanical and Industrial Engineering at the University of Minnesota Duluth, took on these issues of snowplow fleet management. The primary objectives of his study were to investigate how to improve fleet operating costs through effective vehicle replacement, to validate (or challenge) the current vehicle life standard of 12 years, and to understand utilization issues at the Minnesota Department of Transportation.
This research was conducted through the Northland Advanced Transportation Systems Research Laboratories, a program of the ITS Institute that studies comprehensive winter transportation systems and the transportation needs of small urban areas.
For the study, Wyrick used the Equivalent Uniform Annual Cost (EUAC) method as one way to determine an appropriate life-cycle standard for Mn/DOT's fleet, focusing on the class 330 snowplow. This method analyzes the costs associated with owning a fleet asset throughout its life (including acquisition, operation, maintenance, and disposal costs) to reveal the time range with the lowest annualized costs. Over the life of a vehicle, the annualized acquisition cost comes down as the annual operating costs go up. Using EUAC, the researcher looks for the area in the middle after the acquisition cost has gone down enough and before the operating costs have gone up too high. This is the "window of opportunity" for replacing assets, Wyrick says.
Good data were hard to find because of inconsistent entering and tracking of data, but Wyrick was able to make some tentative conclusions based on his analysis. He provided examples from two Mn/DOT districts: District 6, in the southeast corner of the state, and District 1, in the north. The results showed an average optimal life cycle of 10.76 years for District 6, and 9.26 years for District 1. These results were based on total cost per year of the vehicles.
Assuming the results from Districts 1 and 6 can be generalized, if the life cycles of Mn/DOT's snowplows were reduced from 12 years to 8 years, Mn/DOT could save up to $330,000 per year statewide on the class 330 snowplows alone. In addition, there are other, intangible advantages to earlier replacement: newer vehicles get used more often, have improved technology and safety features, and are preferred by operators.
The second aspect of Wyrick's study was utilization—how much the plows should be used each year. Unfortunately, snowplow performance requirements can be contradictory. On one hand, Mn/DOT districts are evaluated by how quickly they get down to bare lane after a snow event, which encourages having more plows to accomplish this faster. However, the standard utilization minimum for snowplows is 3,500 miles a year, which promotes having fewer plows. Wyrick observed that although it's important to use the plows the optimum amount, that amount isn't clear to DOTs because of competing performance measures.
Wyrick says that a statewide life-cycle standard "may not be optimal" because of differences among districts and among individual vehicles. He suggests that life-cycle analysis could be conducted on an individual unit basis to dispose of problem vehicles earlier and to keep reliable vehicles longer. This could be done by using trend analysis, which tracks whether the cost is increasing or decreasing for each vehicle and then replacing those for which the costs are increasing, or by using a control chart, which tries to keep costs between specified upper and lower limits. Better data would be needed for those methods, however, and Mn/DOT has plans to improve its information systems and data-entry practices. Since there is a potential for significant savings each year, the extra effort required for effective life-cycle costing would likely be well worth it. [The final report of this research is available at www.cts.umn.edu.]