A rail brace assembly provides positive support for a stock rail mounted on a switch brace plate. The assembly includes a rail brace that it is installed over a fixed block attached to the brace plate. The block has a slot and a channel that accept a mating rib and tapered wings connected to the underside of the rail brace. The interaction of these elements provides vertical restraint for the rail brace. The brace assembly includes a stop that is secured to the brace plate and a tapered wedge that is disposed between the stop and the rail brace. Upon driving the wedge longitudinally of the rail, lateral force is applied to the rail brace and the rail. The stop and the wedge employ a longitudinally extending tongue and groove to prevent relative vertical movement therebetween. The junction between the wedge and the rail brace is defined by mating convex-concave surfaces. A shear member such as a cotter pin prevents the wedge from being retracted once the wedge has been driven to a desired longitudinal position. Because the wedge cannot be moved inadvertently, lateral force will be applied continuously to the rail brace by the wedge.