Keith Comeau. —MBTA Transit Police

A Haverhill man is facing an open and gross lewdness charge after transit police say he fully exposed his genitals and began urinating on the floor of an inbound commuter rail train Monday.

Keith Comeau, 38, was on board a Haverhill Line train when he allegedly relieved himself at the front of a car in front of roughly 30 to 40 other passengers, witnesses told police.

Police were called to North Station around 1:55 p.m., and Comeau was arrested by transit police.