The Convention Center is offering free parking on Earth Day to anyone who drives a hybrid. They are also using the offer to promote their new affiliation with ZipCars, a car-sharing service.
Earth Day is on April 22.
Source:Boston Common Garage to give hybrid car owners a free day of parking - Boston Business Journal:
"Allowing drivers of hybrid vehicles the opportunity for free parking is a gesture we can make to attract attention to a large environmental movement that promotes healthier driving conditions for the City of Boston," said MCCA Executive Director James E. Rooney.In order to get free parking, you just need to notify the cashier at the exit you are driving a hybrid.