The 509 Harbourfront began service in 1990 as the "604 Harbourfront" and was referred to as the "Harbourfront LRT". It was the first new Toronto streetcar route in many years, and the first to employ a dedicated tunnel, approximately long. The route starts with an underground loop at Union station, runs south along Bay Street to the underground Queens Quay station, then turns west and emerges onto Queens Quay. The line's original terminus was Queens Quay and Spadina Loop, at the foot of Spadina Avenue; beyond this point non-revenue track ran north on Spadina to King, to connect the new line with the rest of the network.