A concrete lid for an in-ground utilities box includes a reinforcement structure filled with concrete. The reinforcement structure includes a plastic frame and one or more reinforcing trusses that extend between opposing sidewalls of the plastic frame. The reinforcing trusses also extend substantially between the upper and lower edges of the opposing sidewalls. For example, a reinforcing truss may include a flat truss member that is substantially coplanar with the lower edges of the sidewalls, and an arched truss member that extends towards (but does not reach) a plane defined by the upper edges of the sidewalls. The reinforcing trusses include openings that allow wet concrete to pass through. The sidewalls of the plastic frame protect the edges of the lid from damage. The reinforcing trusses reinforce the concrete lid, eliminating the need for separate reinforcement material.