Minihawn,
Plexiglass is a trade name for acrylic plastic, Lexan is a trade name for polycarbonate plastic. They are two entirely different things with entirely different characteristics. Polycarbonate is an acceptable possibility, acrylic is not. The Lexan brand of poly is available in green tint to match a windshield.
Robert,
Title 51 of the Federal Transportation Code says that windows must be of a "Shatterproof" material. I have seen this happen before, your state has no authority to rewrite the Federal Law.