The Roosevelt Tunnel built under the Waldorf Astoria to which Ryder uses as part of his escape from the subway is actually based on the secret track 61 which is built under the Waldorf Astoria and was commissioned to help President Franklin Roosevelt keep his use of a wheelchair secret.
Garber talks about choosing between purchasing trains from a Japanese company and a Canadian company. Although not mentioned by name, this refers to Kawasaki Heavy Industries and Bombardier Transportation, who have both manufactured subway trains for New York.
The R-142 and R-142A subway cars portrayed in this film are permanently linked into 5-car sets and cannot operate as single units. R-62A 2079, a single car capable of operating alone, was cosmetically modified to resemble a modern car for this film and restored to its original appearance after filming was completed.
Ryder says to Garber, "You live, you die, you either go with the current or you fight it, but you all end up in the same place", to which Garber asks, "Where's that, Jersey". Ryder then says, "Yeah, you watch it, I was born there man." John Travolta, who plays Ryder, was born in Englewood, New Jersey.
The movie pays homage to Walter Matthau, who played Lt. Zachary Garber in the 1974 movie by naming 'Denzel Washington's character Walter Garber. Also, while Lt. Zachary Garber wore a plaid shirt and yellow tie, Walter Garber wears a yellow shirt and similar pattern plaid tie.
In the movie, from the audience's viewpoint, Ryder (John Travolta) is seen wearing an earring on his right ear while Walter Garber (Denzel Washington) has one on his left. Also notice that both of them has only a single earring.