oval shaped locator section 37 of a track bolt 36 the section 37 having a pair of oppositely spaced flat sides dimensioned to be snuggly received in the apertures 33 and 35 whereby to preclude rotational movement of the bolt 36 the base plate 32 is connected to the flange of the running rails 12 and 14 by a pair of rail clips 34 each clip being secured by a suitable nut 38 threadably engaged to the bolt 36 the adjacent marginal edges of the slabs 22 and 24 relative to the running rails 12 and 14 are immovably retained or secured by a pair of angle shaped hold down brackets 40 the latter also being retained by the bolts 36 via a suitable anti vibration lock nut 42 correspondingly the outer marginal edges of each of the slabs 24 are similarly retained to the base plate 32 via assembly of an end bracket 44 a track bolt 36 and a lock nut 42 if desired the space between the marginal edges of the slabs 22 and 24 and the running rails 12 and 14 may be filled by a suitable material indicated at 41 which by way of example can be a rubber or bituminous filter as previously indicated each of the center and end slabs 22 and 24 are preferably cast in eight foot modular sections with each section having a depth or height of 5 or 6 inches whereby to facilitate installation with all forms of standard rail sections each of the modular slabs 22 and 24 are precast of one piece monolithic construction and dimensioned to provide a 21 4 to 21 2 inch flangeway opening between opposite lateral sides of the head section of the running rails and.