Abstract: A construction toy system is disclosed for the assembly of a guide track structure for a wheeled vehicle. Basic structural components, comprising rod-like struts and molded plastic connector elements adapted for snap-together attachment to the strut elements, enable support structures to be assembled. One or more guide track elements is provided, preferably in the form of a continuous, slotted flexible tube, typically formed by extrusion of plastic material. Special track-mounting connector elements are formed with track-mounting lugs which extend through the slotted side of the tubular track element to provide internal support. Track-mounting lugs are positioned at spaced points throughout the structure, providing spaced support for the track element. The flexible track element is self-supporting between mounting lugs, and conforms readily and smoothly to vertical and horizontal contours of the structure.