When we reached 42nd Street, an enormous convoy of NYPD cars started driving down 5th Avenue, lights flashing and sirens blaring.  At first we thought that we were going to witness a foiled terrorist plot or a drug bust.  But wait....why were they driving so slowly, as if they were in a parade?  Just as strangely, most of the people on the street continued to go about their business as if this was the most normal occurrence in the world. We later discovered that this is one of many routine anti-terrorist measures which have been taken since the 2001 attack on the World Trade Center.