From Gotham Gazette:
A person can plead not guilty of a parking offense by mail, on the internet or in person. The problem though, is that the New York City Parking Violations Bureau and the Department of Finance require the driver or registered owner to pay the fine within 30 days. Pleading not guilty by mail or on the internet may result in a determination more than 30 days later. Paying the fine upon a finding of guilt then could entail a late penalty for the 30 days the not-guilty plea was under consideration. So someone who does not pay the fine, pleads not guilty and is found guilty must pay not only the original fine but also the penalty for late payment.
The Parking Violations Bureau adjudicated 1.27 million parking summons at in-person hearings in 2009, according to Dennis Boshnack, a Queens attorney with expertise in parking violations cases and a former Parking Violations Bureau administrative law judge or hearing officer. Writing in the New York Law Journal, Boshnack maintains that most drivers give up their fight because they are representing themselves and cannot continue litigation alone and/or pay lawyer's fees that can easily cost more than the fine itself. The small amounts of money involved in individual cases make suing the Parking Violations Bureau "unaffordable or impractical."