Ten years ago, Nashville Electric Service, one of the 12 largest public electric utilities in the United States, had tree-related outages 10 times that of utilities following vegetation management best practices. Today, it is reaping the rewards of a well-funded, well-established vegetation management program that has resulted in best-practice reliability indices.

The Problem

In September 2000, R.W. Beck performed a system assessment for Nashville Electric Service (NES). The assessment indicated that tree-related maintenance was inadequate. It was leading to excessive breaker operations and contributing to increased equipment failure, higher maintenance costs and a higher frequency of outages. The main culprit was trees along power lines that had not been consistently trimmed.

In October 2001, Environmental Consultants Inc. (ECI) performed a study on the utility's tree-trimming practices and found that its tree-related outages were 10 times greater than that of best-practice utilities. NES also had the highest number of tree-caused outages per 100 miles of line of all 110 utilities ECI had studied to date.

NES system statistics showed that tree-caused outages were 19% to 21% of the total outages. This was costing the utility more than US$3 million per year in overtime pay for outage restoration. Needless to say, the system was in bad shape and drastic changes were needed — and needed quickly. The system had 162 trees per pole mile compared to the 75 to 100 trees per pole mile of best-practice utilities. Additionally, rear-lot lines were grown up, making it difficult to locate poles and power lines. Tree line contact on distribution and transmission systems was higher than best-practice utility standards, as was the brush component of the workload. Crew productivity was also below standard because of the high number of trees involved.

Past funding for tree trimming had been inadequate for several years, making it difficult to deal with the many dead, damaged, dying and diseased trees on the system. NES basically needed to establish a reclamation project to clear the rights-of-way and rear-lot lines. The large amount of ingrowth brush had to be reduced, and the high volume of 4-inch (102-mm)-plus trees growing on the system had to be removed.

The primary objective in developing the vegetation management program was to improve and then maintain customer service reliability. An additional objective was to achieve optimum results in the first trim cycles while spending the least amount of money.

The Action Plan

To accomplish the goals, current conditions were evaluated, desired results were determined and then a timetable was developed to accomplish those results. Public government officials and customers had to be educated on why a more-aggressive trimming program was needed.

However, gaining the support of NES management and power board was the most important key to accomplishing the goals. This was necessary to develop adequate funding to implement the program. Their support would also be key in addressing the anticipated resistance of external and internal customers.

Early in the process, a plan to effectively communicate with the public, Nashville government officials and council members, local city mayors and NES management was developed. Input about the plan was also solicited from other utilities, customers, local tree groups, government officials and a consulting firm who helped develop the plan. Current and future staffing needs were evaluated in order to develop the short- and long-range budgets, so that once a regular trim cycle was reached, it could be maintained.

Pride and egos had to be put aside and outside-of-the-box thinking was truly needed from the beginning to develop benchmarks and performance audit criteria. To help in this area, NES used geographic information system (GIS) technologies, including geodatabase viewing application, aerial photos and ESRI's Arc 3GIS, during the planning stages, while using laptops in the field to help plan as the work progressed. Frequent meetings were needed to reevaluate the work process.

Communicating the Plan

In July 2002, NES announced to the Nashville community the new, accelerated vegetation management program designed to reduce the number of tree-caused power outages customers were experiencing while protecting the health of the trees.

From the beginning, communications was a key element to the operation. The priority was to communicate with the board and management team early and often. From the beginning, the program had the complete support of the board and management team. Whenever a problem occurred, they remained committed to the program 150%, seeing problems as opportunities. Meetings and workshops were also held for customers and concerned citizens, government officials and local tree organizations to explain the program in detail.

Like most communities, Nashville residents consider trees an attribute that adds to the beauty of the city. To maintain that beauty, NES formed a partnership with ACRT Inc. to assist in work planning and auditing of the tree trimming crews. From the beginning, ACRT was a valuable team member and useful resource for information.

At the busiest point, there were 12 work planners and six auditors from ACRT working with NES to oversee the work. The planners pre-planned the circuits and made customer contacts, while the auditors audited the work of the contract tree trimmers. Currently, there are eight work planners and five auditors.

To keep customers informed, postcards were sent telling them of plans to trim along their circuit. This was followed up by an interactive voice response (IVR) message informing customers when planning work on their circuit was to begin. A second IVR message informed them of when trimming would actually begin. In order to resolve training issues with the regular customer relations representatives, a NES vegetation management hotline was established and manned by staff trained and experienced in vegetation management activities.


When the program began, the contracts were lump sum and time and material (T&M). NES quickly realized the productivity needed was not coming from the T&M contracts, so the number of T&M crews was drastically cut and contracts with lump-sum trim with unit removal terms were favored. At present, NES uses contracts with lump-sum trim with unit removals for a period of one year.

There was also experimentation with a hybrid T&M with unit trim and removal contracts, instead of a standard T&M. Only enough T&M crews are used to work on damaged, dead, diseased or dying trees that need immediate attention. When the T&M workload drops, personnel are transferred to unit crews. And, when absolutely necessary, personnel from unit crews can be pulled to work on T&M crews.

After Three Cycles

When work began in 2002, the goal was to get the system back into shape using a three-year trim cycle. The third three-year cycle was just recently completed. In addition to other benefits, results indicate the cycle can now be lengthened to a four-year trimming. There were several focuses of the recent three cycles:

  • Removed 118,502 units of brush less than 4 inches, equivalent to 1360 acres (550 hectares) of brush

  • Removed 339,414 trees, of which 85% of the trees were less than 16 inches (406 mm)

  • Reclaimed rear-lot lines.

Going forward, one of the major potential problems will be monitoring cycle-buster trees. Species data was collected in prior cycles to allow identification and location of all cycle-buster species. This will allow observation of the trees to determine whether trimming is needed or growth inhibitor.

Measure of Success

Currently, Nashville Electric Service's tree-related outages are only 6%, with 3.5% of those outages caused by branch and tree failures. All of the average service availability index, customer average interruption duration index (CAIDI), system average interruption frequency index (SAIFI), system average interruption duration index (SAIDI) and momentary average interruption frequency index (MAIFI) goals are being met. Back-lot lines are cleared and, typically, crews can see four spans clearly. Tree line contact is now non-existent and much of the brush component has been eliminated. This alone has improved crew productivity tremendously. Now, NES averages 60 to 100 trees per pole mile, which follows the statistics of most best-practice utilities. This was accomplished by concentrating on brush less than 4 inches in diameter, removing trees with a 4-inch diameter or greater, 20 ft (6 m) from the inside phase and average sized trees that averaged 85%, 12 inch (305 mm) and smaller.

The current budget has been reduced 48%, returning to that of the budget level when the pre-reclamation project began in fiscal year 2001-2002. The NES vegetation management program is part of T&D operations and has a staff of nine: six certified arborists, one of which are utility specialists; one planner coordinator; one operations clerk; and one vegetation manager. Without this dedicated team and all of the contractors, the accomplishments of the last three trim cycles would not have happened. At times, especially when working outside the box, the comfort level was non-existent. As a result, a monumental task has been completed and the system is at the best-practice utility level.

Glenn Springer (gspringer@nespower.com) is vegetation manager, T&D operations, at Nashville Electric Service. He has a bachelor's degree in forestry and 22 years of experience in utility vegetation management, with a total of 36 years of experience in the field of forestry. Springer is a past chairman and has served on the Metro Davidson County Tree Advisory Committee for the past 16 years. He has made numerous presentations on lateral trimming and utility trimming to various local groups and others representing communities and utilities across Tennessee.

Companies mentioned in this article:

ACRT Inc. www.acrtinc.com

Environmental Consultants Inc. www.eci-consulting.com

ESRI www.esri.com

Nashville Electric Service www.nespower.com

R.W. Beck www.rwbeck.com