An effort by five area communities to jointly market their combined stretch of Route 3 to prospective businesses is picking up speed. Bedford, Billerica, Burlington, Chelmsford, and Lowell have devised a brand name – Middlesex 3 — or their shared highway corridor, along with a logo. The communities recently formed a nonprofit – The Middlesex 3 Coalition – to spearhead the initiative, and have begun recruiting businesses and other groups to join them.