BRISTOL — Dennis Hopkins was waiting late last month at the stop sign at Walpole Meetinghouse Road, where he lives. Across Route 130, a worker from Asplundh Tree Expert Co. was high above the highway in a bucket, pruning pine and maple branches away from the power lines.

This was a welcome sight for Hopkins. The entire Pemaquid peninsula, a rocky claw reaching south from Damariscotta into the Gulf of Maine, is served by a single electrical circuit. It connects small businesses along highways and summer cottages on dirt roads, via a 211-mile web of wire laced through the woodsy landscape.

The problem is, a stiff wind can turn out the lights for the 4,097 customers who live here, making the area one of the worst for electricity interruptions in Central Maine Power Co.’s service territory. Power went out 115 times in 2011.

“It’s bad enough that we invested in a generator,” Hopkins said.

That generator might not get fired up as much in the future.

Falling trees and branches that touch overhead lines are the leading causes of power outages in Maine, the most heavily forested state in the country. In response, CMP is into the fourth year of a five-year maintenance program of aggressive tree pruning. Last year it trimmed back trees along 110,000 pole spans.

This effort is showing results, according to data filed with the Maine Public Utilities Commission. Stepped-up trimming, along with other measures, has begun to reduce greatly the number and duration of power interruptions for CMP’s 607,000 customers.

The work is taking place during a period that has seen extreme weather in the Northeast topple trees and knock out power for days to millions of customers. Last August, it was tropical storm Irene; last October, the Halloween Nor’easter; early last month, the violent storms that crippled cities from New Jersey to Virginia. Late last month, environmental advocacy groups in Maine released a study contending that rain and snowstorms in New England are becoming more intense and more frequent.

No two storms are alike, and it’s not possible, or desirable, to prune every tree near a power line. But the Maine PUC, which ordered the tree-trimming program in 2008 and oversees its progress, says CMP’s local distribution system today is the most reliable it has ever been.

“Short of putting everything underground, which is prohibitively expensive, tree trimming is the best way to keep the wires humming,” said Tom Welch, the PUC’s chairman.

The tree program is part of the commission’s alternative rate plan for CMP, which penalizes the company when it fails to meet performance standards that become stricter each year. The program costs ratepayers $22 million annually.

Next year, the rate plan is up for renewal. Welch and the other commissioners will review the tree program, and they will decide whether CMP’s distribution system can or should be made even more reliable, and what that could cost.

Longtime Maine residents recall the impact of the 1998 ice storm and may have come to accept the prolonged outages as unavoidable. However, CMP’s distribution system simply wasn’t as dependable then.

A consultant hired by the PUC in 2007 noted that system reliability was poorer than average when compared against national utility indexes. It also found CMP’s tree-releated outage rate was among the highest in the industry, accounting for 42 percent of all power losses in 2005. At the time, CMP was trimming trees in a cycle ranging from seven to eight years.

This assessment helped form the basis for today’s tree program.

Along Route 130, a worker armed with a brush saw moved up and down among the trees and wires in a 70-foot bucket. His assignment was to cut any branch within eight horizontal feet of a wire, and 15 feet above and below. It’s a careful, methodical process, performed around live wires. On the ground, co-workers fed the downed limbs into a chipper.

After the tree crew finishes, CMP workers inspect the wires and every pole for rot or broken cross arms.

“At this level, it’s a span-by-span operation,” said John Carroll, CMP’s spokesman.

The program has put 145 trimming crews on the road year-round, essentially giving a haircut to 20 percent of CMP’s 23,809-mile service territory every year. Viewed another way, they will visit 646,724 pole spans over five years.

Halfway through year four of the program, this detailed approach is paying off. In 2011, tree-related incidents fell to 28 percent of all outages, from 42 percent in 2005.

The tree program has contributed to overall improvements in keeping the lights on, and is reflected in utility-industry indexes used by state regulators. These indexes measure how often, on average, power is interrupted for a customer, and how long it stays out.

As part of CMP’s alternative rate plan, regulators set targets that get harder to hit each year. In general, CMP has been achieving or beating the goals.

For instance: For average outage duration, the PUC set a target this year of slightly more than two hours. In the first three months of 2012, outages lasted an average of less than one hour and 40 minutes.

These numbers are meaningful to regulators, but customers worry most about losing power for a long period during storms.

During last fall’s freak snowstorm, roughly 207,000 CMP customers were in the dark at some point by mid-Sunday, Oct. 29. It was one of the most widespread outages in 20 years. By Monday morning, the number of customers out had dropped to 20,000, thanks to the work of 200 line-repair crews and 110 tree crews.

By comparison, some customers in Connecticut were in the dark for a week. In Massachusetts, thousands of people waited for days to have power restored.

Late last month, Massachusetts Attorney General Martha Coakley announced that she was seeking more than $16 million in fines against the regional utility, National Grid, for what she said was the company’s poor performance in restoring power after the October storm, and after Tropical Storm Irene.

In Maine, CMP’s trim program helped reduce outages by removing dead limbs and diseased trees that often come down during storms, according to Carroll. By contrast, officials in Connecticut acknowledged they had not been aggressive enough with tree maintenance over many years.

“When our crews went down there to help, they couldn’t believe the number of large trees so close to the system,” Carroll said.

Although CMP’s service quality has improved overall, many trouble spots remain. Typically they are in rural, heavily-wooded areas served by single circuits. The latest annual report to the PUC lists 19 “underperforming” circuits last year.

CMP is improving these circuits in 2012. Beyond enhanced tree trimming, guards to discourage squirrels and other small animals from shorting out circuits are being installed. Circuits are being reworked, so breakers can be reset from more than one place if a substation malfuctions.

One major upgrade is planned for Harpswell, where the line running to Orr’s Island is considered one of the worst-performing in CMP’s system. Power went out 120 times last year, resulting in a total outage time of 118,953 hours for customers on the line.

Beyond tree problems, the Orr’s Island run suffers from wire that dates to the 1940s and literally is burning up. The work will cost $1.7 million.

“Replacing 96 out of 150 poles down that stretch of road on a live circuit is complicated,” Carroll said, “but we’re getting set to start work this month, with a goal to complete by the end of the year.”

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