At a special town meeting Monday night, Chilmark voters approved a $500,000 purchase of two lots for the Middle Line Road affordable housing project, further voting to shift the entrance to Middle Line Road.

The town will construct roadway over the lots to create an improved sight line at the junction of Middle Line and Tabor House roads.

The move addresses concerns of the Martha’s Vineyard Commission and the town planning board that the current turn-in to Tabor House Road poses a safety risk in the face of development plans.

The town will spend $275,000 on a .72 acre lot off Tabor House Road, now owned by Beverly Gillis Jaksa, and $225,000 on an adjacent .7 acre lot now owned by Walter A. Jenkinson Jr., Blair Emin and Keith Emin. Agreements between the town and the current owners have already been signed.

Two articles relating to the purchases were passed by an overwhelming majority of the 71 voters present, with just four nay votes registered in both cases. A two-thirds majority was necessary to secure passage of each article.

A third article, requesting approval to close off the present access on Tabor House and Middle Line Roads and to reroute the access road over the two properties, was unanimously approved.

The town will use community preservation funds to cover the purchases. The funds are generated through a tax surcharge which is matched by state funds, meaning that Chilmark taxpayers will pay half of the costs.

The plan calls for placing six residential houses and a building with six rental apartments on seven lots on a 21-acre plot on Middle Line Road.

Voter Dan Greenbaum questioned the expense, arguing that the sight line issue on the road is no more significant than that of other, well-worn Chilmark streets. “It’s a huge investment for a very small problem,” Mr. Greenbaum said.

Selectman J.B. Riggs Parker responded: “I wish it were simple like that,” he said, “But the Martha’s Vineyard Commission and the planning board have insisted that for the substantial increase of use the entrance is not safe.”

The two lots will also create a patch of open land between the capped town landfill and the affordable housing site, which will permit a walking trail joining Holman and Middle Line Roads with the road to Peaked Hill.

“We would be concerned that people might buy that land and build near to the landfill,” Mr. Parker said. “This will provide a green-zone buffer between the properties and the dump.”

Two last-minute amendments to the warrant will halt the project should the results of an archeological dig, being carried out this month, show that the site has historical significance.

The amendments were added when a worked flint was found in a test pit at the site during initial excavations conducted by the University of Massachusetts, providing evidence of Native American presence in the area.

“We don’t want to disturb any Native American burial grounds,” selectman Warren M. Doty said after the meeting. “If we find this sort of thing, we want to be able to stand back.”

Monday night’s vote brings total costs to just over $1 million for the Middle Line Road project, which is the first proposed town-sponsored affordable housing program for Chilmark.

Action on the Middle Line project began back in 2004, when voters authorized a $260,000 borrowing to purchase rights for the land parcel.

Mr. Doty sees no end in sight. “I’m on record as saying this would be completed by November 2007,” Mr. Doty said after the meeting. “So my predictions are worthless.”

At the meeting, Mr. Doty thanked voters for their continued support of the project. “We’re plugging away,” he said, adding: “Thanks for voting ‘yes’ tonight.”