State officials are reminding drivers to stay clear of the breakdown lanes on a section of Route 128 southwest of Boston now that a fourth travel lane is open.

Since the opening of the fourth lane on Route 128 between Route 24 in Randolph and Route 109 in Westwood-Dedham in both directions in November, the breakdown lanes are now reserved for disabled motor vehicles and emergency vehicles.

The Federal Highway Administration had allowed breakdown lane use on this section of Route 128 during weekday peak travel periods since 1986. State Police said they hoped increased patrols combined with signage would remind drivers the lane is now off-limits.

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The 5.7-mile lane addition cost the state $136.7 million in several contracts. The state is also working to add fourth lanes from Route 109 to Route 9. Until that project is completed, breakdown lane travel is allowed on that stretch during weekday peak travel periods, from 6 a.m. to 10 a.m and 3 p.m. to 7 p.m., said Transportation Department spokesman Michael Verseckes.