By N. Clark Judd

City Councilman Oliver Koppell isn't taking the city Department of Transportation's recent refusal to install a turn signal on Riverdale Avenue and West 254th Street lightly.

At a press conference last week, the incensed elected official demanded that the mayor fire DOT Commissioner Janette Sadik-Khan after, Mr. Koppell said, she reneged on a promise to install the turn signal, which he believes would help ease traffic at the busy intersection.

Mr. Koppell fired off a letter to Mayor Michael Bloomberg on April 30 calling for Ms. Sadik-Khan's dismissal, a day after receiving the news that the city agency had denied his request. "This situation is indicative of an attitude and approach that is incompatible with her proper responsibilities as commissioner," wrote Mr. Koppell.

The councilman and other community leaders have been asking for a turn signal for the past four years at the North Riverdale intersection, which serves as a valve in the traffic flow to the Riverdale Metro- North train station and the Salanter Akiba Riverdale Academy. Drivers going northbound on Riverdale Avenue, fed by the nearby Henry Hudson Parkway, turn left on to West 254th Street en route to both of those locations. Just up the street sits the Robert J. Christen School, PS 81. The councilman feels the turn signal would alleviate traffic by allowing northbound cars to turn onto West 254th Street without having to race to beat oncoming southbound traffic.

DOT officials say they have studied the site four times since 2002 and found that based on accident rates and traffic flow, the corner did not warrant a signal.

Mr. Koppell admits that, by his count, there have been relatively few accidents at the intersection - 11 in 2007 from January to October, according to another letter sent to the DOT from his office last year - "but there's the potential for more accidents," he said at the April 30 press conference he held at the site to announce his demand for Ms. Sadik-Khan's ouster.

DOT officials said that only three accidents at the intersection in the past three years were related to a left turn.