A teenager was killed when he popped his head out of a rooftop hatch on a double-decker bus and struck an underpass near the George Washington Bridge on Friday night, an official at thePort Authority of New York and New Jersey said.

Daniel Fernandez, 16, was traveling to a birthday party in New Jersey on the crowded party bus, which had just crossed the bridge and was trying to enter Interstate 95 when the teenager hit his head on the bottom of the Fletcher Avenue underpass around 6:45 p.m., the authorities said.

The police were investigating the accident late Friday, causing major traffic delays for motorists heading out of the city.

Mr. Fernandez was part of a group of 65 teenagers who had boarded the bus at St. Francis Preparatory School in Queens and were headed to a Sweet 16 party in New Jersey, said Steve Coleman, a spokesman for the Port Authority.

The bus was operated by Designer Limo. The company could not immediately be reached for comment, but its Web site describes its double-decker buses as custom designed to create state-of-the-art nightclublike surroundings.

Mr. Fernandez was rushed to Hackensack University Medical Center, where he was pronounced dead on arrival, Mr. Coleman said.