Four towns have joined the Middlesex 3 Coalition, an economic development group with a focus on improving transportation along the Route 3 north corridor.

Lexington, Tewksbury, Tyngsborough and Westford join the group’s existing membership of Bedford, Billerica, Burlington and Chelmsford. Last week’s announcement came during a forum in Billerica on strengthening the region’s manufacturing economy.

The nonprofit coalition includes members from the public and private sectors and educational institutions. It recently formed a Transportation Management Association, which will add local shuttle buses to local employers. Lahey Health contributed $100,000 in matching funds toward the trial shuttle service.

The organization also sponsors workforce training programs, helps businesses find development sites and assists with permitting.