Free parking in the heart of Manhattan? It might seem impossible. But a new study says more than half the drivers who throng midtown and downtown Manhattan aren't paying for parking -- and everyone else is paying in terms of congestion.The study says 38 percent of drivers get free parking or are reimbursed for it through their jobs. And another 19 percent find street parking without meters.That might be a nice break for the drivers. But the group that commissioned the study says the availability of parking encourages driving instead of other forms of transportation -- and that means more traffic and pollution.The group is called Transportation Alternatives. It advocates for public transit and other transportation options besides driving.The study findings were based on a survey of more than 1,600 drivers.