The Massachusetts Turnpike plans to install a new $12 million safety barrier in the median of the Boston Extension, the Turnpike Authority announced recently.

Work began March 1 on the 42-inch concrete barrier, which will run seven miles from Interchange 15 at Weston and Interchange 18 at Allston/Brighton.

Crews will perform work on the project from 7 a.m. to 3:30 p.m. and from 8 p.m. to 5 a.m. during the week, as well as on weekends. During the construction of the new barrier, speeds along that section will be reduced to 45 mph, and lanes will be narrowed to 11 feet wide.

Some lane closures will occur during the work, but the Turnpike Authority said in a statement that those closures would occur only during non-peak travel hours, and any closure that caused more than a 10-minute travel delay “will be halted immediately.”

The project will also include new lighting and wiring to provide more reliable lights and to reduce highway headlight glare at night.

Work is scheduled to be completed on the new median barrier by Dec. 23, 2004. However, that will not end work on the Boston Extension. The Turnpike Authority said repaving of the extension would begin in 2005.