#321 on a mobile phone or 888-359-9595. It's the Mass. Highway Department's new 24-hour report-a-killer-condition hotline:
Drivers are advised to pull onto the shoulder, completely out of travel lanes, before making a call.
You can also report dangerous conditions via the Web, although MassHighway says that page is only staffed during business hours.
Ed. snarky but still legitimate question: What if the dangerous condition is on the turnpike, the Tobin Bridge, etc.? Will MassHighway wake somebody up at the turnpike authority to fix the problem?