The A666 is a major road in Greater Manchester and Lancashire, England. Known as Manchester Road, Bolton Road, or Blackburn Road, depending on which area it is in, it runs from its junction with the A6 and A580 at the Irlams o' th' Height boundary with Pendlebury near Manchester, through Pendlebury, Clifton, Kearsley, Farnworth, Bolton, Darwen and Blackburn before meeting the A59 at Langho.