Question: Derby Racer was the name of how many wooden roller coasters that operated at Revere Beach in Revere, Massachusetts, both coasters were racing roller coasters, with side-by-side track pairs where two coaster trains would race each other around the circuit of the coaster, a roller coaster train is a vehicle made up of two or more cars connected by specialized joints which transports passengers around a roller coaster's circuit?
Sentence (from "Lightning (Revere Beach)"): It was one of the infamous Giant Cyclone Safety Coasters which were constructed by noted roller coaster engineer Harry G. Traver in the mid-1920s (the rides were, in fact, anything but safe, and became known as the "terrifying triplets").
Relevant evidence: No