When travelling down the left lane on Cambridge Street towards Sturrow, it becomes a left turn ONLY lane at Charles MGH Station. The center lane is the ONLY lane shown to go straight and the center and right lanes are available for turning right. This is CLEARLY marked by the huge green traffic sign prior to the station. Too many times I've been thisclose to getting my car hit by cars that make (mostly) unsignalled, (always) unsafe lane changes. This especially happens most dangerously when there are cars waiting in the left turn only lane. The car in the left lane will attempt to go straight OR will attempt to make the right turn to either of the Sturrow Drive onramps.