I believe in some cities, the city government places a small camera at
traffic intersections that photographs the license plate of any car
the runs a red light and/or "blocks the box." The City then fines the
owner of the offending car. This reduces traffic congestion and
traffic accidents while providing the City with revenue from the
fines.

I was told that New York City may have only a very limited number of
such cameras because of a New Yortk State law.

My question is:
Is there such a State law? Is there a limit or impediment of any sort?
What is the reason for the limit if it exists?

Since 1993, when New York City's red light camera program began, the
program has been legally in a "demonstration" phase. This limits the
number of cameras and requires extensive reporting of statistics
related to each camera-equipped intersection. The "demonstration" has
been extended through 2009. There have been efforts to induce the
state legislature to declare the "demonstration" permanent and enable
the city to install more cameras and perform less paperwork, but until
and unless such a bill is passed by the legislature, New York City
will be restricted to having only 50 such cameras in operation. In the
past, such bills have faced opposition because of privacy concerns.
From what I have read, it looks as if the bills have also been used as
political footballs by legislators such as Sheldon Silver, who
apparently has opposed this kind of bill because he wanted to
negotiate changes in the city's fire department.

Although many more than 50 red light cameras may be spotted around New
York City, some are nonfunctional "decoys." The city, for obvious
reasons, won't tell the public which ones are real.

"The authority to use no more than 50 red light cameras in New York
City is Section 1111-a of the Vehicle and Traffic Law. Bill A11663
passed the New York State Assembly on 12 August 2004 to extend Section
1111-a until 1 December 2009."

NYC Red Light Camera Locations
http://deepcreekyachtclub.com/WebPage/NYCTrafficLightCamera.html

"August 17, 2004...
Transportation Alternatives scored a major victory last week when the
New York State Assembly finally approved A.11663/S.7599, the extension
of New York City's successful red light enforcement camera program.
The bill, which had been held hostage in the State Assembly, will
extend the program for five years and bodes well for the future
passage of additional enforcement cameras.

While significant, the win is bittersweet. T.A. and our allies on this
issue--the Tri-State Transportation Campaign, the City Department of
Transportation, the Mayor, Queens State Senator Frank Padavan and
Queens State Assemblymember Mark Weprin--had hoped that the state
legislature would also agree to expand the red light enforcement
camera program from 50 to 100 cameras."

Transportation Alternatives: Red Light Enforcement Cameras Saving Lives
http://www.transalt.org/press/askta/040818.html

This is the Google search string that led me to the relevant information:

Google Web Search: "new york city" "red light cameras" "no more than * cameras"
://www.google.com/search?hl=en&q=%22new+york+city%22+%22red+light+cameras%22+%22no+more+than+*+cameras%22

I hope this is helpful! If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud