Debate continued last week before the Martha’s Vineyard Commission over Verizon’s plan to raise a communication tower in Vineyard Haven from 77 to 138 feet.

Verizon wants to raise the tower to preserve a line of sight with the mainland.

The commission is reviewing the project as a development of regional impact, in part because the tower stands within a district of critical planning concern that protects Island roads.

Attorney Geoghan Coogan, representing Verizon, said tall trees north of the tower on Edgartown-Vineyard Haven Road already interfere with the signal, which provides all land line service to the Island, including for police, fire and emergency services.

“This tower is vital to the Vineyard,” he said.

The tower also provides internet access and reroutes service from Nantucket.

Property owners north of the tower have refused to allow Verizon to remove trees, leading to the proposal to extend the tower instead. At their meeting last Thursday, commissioners pressed for more details.

DRI coordinator Paul Foley noted the possibility of relocating the tower farther from the road, but Mr. Coogan said other trees might be in the way. Commissioner Michael Kim asked if other alternatives had been pursued.

In response to the idea of using fiber optic cable instead of microwave technology, Verizon representative David Dolch said it would cost millions to lay cables along the bottom of Vineyard Sound.

Mr. Kim pressed further, suggesting that Verizon look into adding more towers of the same height. “It doesn’t appear that any study other than an intuitive one was made,” he said.

As part of the project, the existing microwave dishes would be moved farther up the tower and a new eight-foot dish would be added at a height of 128 feet. An appurtenance at the top of the tower would bring the total height to 138 feet.

Much of the discussion focused on the three or four trees that Verizon has identified as threatening the signal. DRI coordinator Paul Foley estimated based on photographs that the trees are around 80 feet tall. Some have questioned whether the trees would ever get tall enough to block the signal.

Ellen Cummings, another representative for Verizon, said she was told some time ago by Fred Lapiana, the town tree warden at the time, that trimming the trees was not an option since the trees would die. In response, she said, she reached out to property owners about removing the trees with no success.

Commissioner Doug Sederholm asked if the property owners knew that if the trees didn’t come down, the tower would be raised. “I’m curious as to whether any compensation was offered,” he said. “And I’m curious as to what it would cost to increase the tower height compared to what it would cost to buy those trees and make them disappear.” He said arborists routinely examine trees to determine their monetary value.

Commissioner Clarence A. (Trip) Barnes 3rd noted that a previous extension of 17 feet in 1986 had maintained the line of sight for 31 years. “It seems like a big jump,” he said of the proposal.

Mr. Dolch said a direct line of sight with towers on the mainland may not be enough to ensure service, since objects on either side of the line can interfere with the microwaves. “You don’t want just the center point clear,” he said. He couldn’t say how much of the signal was now being lost from interference.

Two abutters expressed concerns.

Nancy Langman noted uncertainty surrounding the health effects of living near microwave radiation, and said the current tower is poorly maintained with coverings that flap in the wind and an apparent osprey nest atop the highest dish.

Charles Noonan, who had concerns related to property devaluation and quality of life near the tower, said that the osprey nest was the tower’s only redeeming feature. In response to concerns about microwave radiation at the site, Mr. Dolch said radiation levels would not increase as a result of the project.

Other concerns related to the stability of the tower’s foundation after so many years, and the fact that if the tower were to fall to the west it would land in Edgartown-Vineyard Haven Road. Commissioner Fred Hancock asked for more information related to an FAA requirement that the tower include a beacon.

The hearing was continued to Oct. 5.