two side - by - side tracks form a closed loop having a curve at each end ; the tracks support vehicles each of which moves around the closed loop as a result of impulses supplied to it by an improved vehicle - propulsion device located entirely within one of the curves for manual actuation by a child - user , and characterized by a novel propulsion arm which tilts upwards into its operating position about a fulcrum in response to an actuating force transmitted by a flexible tape which also causes said arm to rotate horizontally about a shaft .