Integral and semi-integral abutment bridges (SIAB) offer significant advantages over conventional bridges with expansion joints, including improved durability and reduced long-term maintenance requirements. However, conventional SIAB systems continue to rely on physical bearings, which are susceptible to potential maintenance issues and replacement. A novel deck-extension sliding semi-integral abutment bridge system is then proposed in which conventional bearings are replaced with low-friction sliding interfaces. The proposed system incorporates sliding surfaces between the superstructure and the top of the abutment, as well as between the underside of the deck extension and the top of the abutment backwall. By accommodating thermal movements through sliding rather than bearing deformation, the proposed system would also reduce/eliminate the passive earth pressures developed behind the abutment during bridge thermal expansion. An experimental program evaluated the cyclic frictional behavior of conventional polyethylene and ultra-high-molecular-weight polyethylene interfaces as two candidate interfacial materials. Results are promising for the proposed bearing-free (sliding) semi-integral bridge abutments.