Due to accidental vehicle impacts, bridge barriers are prone to local damage and excessive cracking. Also, using de-icing salt in winter results in steel bar corrosion and concrete spalling. Concerns have arisen regarding the feasibility and economics of their repair or replacement. Two key issues can be identified when considering the repair of existing barriers using glass fiber-reinforced polymer (GFRP) bars. The first issue is the design demand, expressed in terms of the applied moment and forces resulting from vehicle impacts. The second issue is the barrier’s capacity to meet this design demand. In barrier replacement, post-installed GFRP bars connect the new barrier to the deck overhang. This paper investigates the barrier-deck joint capacity affected by the GFRP bars post-installed in the existing deck slab using epoxy. It summarizes the experimental results performed on actual-size TL-4 and TL-5 bridge barrier segments, each 900 mm long, aiming to qualify this design for sustainable construction practices. The two barrier segments were mounted over a non-deformable deck slab overhang. The failure of the barrier-deck specimens was observed to be due to concrete breakout at the end of the embedded GFRP bars in the deck slabs, with flexural cracks appearing in the barrier wall. The experimental failure loads were greater than the factored applied load at the barrier-deck interface obtained from finite element modeling, thus providing confidence in the proposed post-installed GFRP bar technique.