In jointless bridges, expansion joints are eliminated. Consequently, girder deformations caused by thermal expansion and contraction are only partially absorbed by the approach slab, while the remainder is transmitted through this slab into the backfill and the connecting road. Distress in the approach slab is a common issue that adversely affects the service performance of jointless bridges. In certain engineering applications, an inclined approach slab buried within the backfill underneath the connecting road-referred to as a buried inclined approach slab (BIAS)-has been employed. The structural response of both the jointless bridge and its approach slab depends strongly on the interaction among the approach slab, backfill, and connecting road. To achieve a more favorable stress distribution in the backfill and connecting road, shear projections are proposed for installation on the upper surface of the BIAS. To clarify the interaction mechanism of the BIAS with shear projections, backfill and connecting road system, the system was designed and constructed. The absolute displacement of the approach slab, the relative displacements between the girder and approach slab, and the soil pressure at the approach slab end face were monitored in the field. A finite element model (FEM) of this system was then developed in PLAXIS and verified using the monitored data. The results demonstrate that excluding the connecting road causes plastic failure and substantial deformation in the backfill. Conversely, when the connecting road is included, the backfill maintains better integrity; even though the deformation zone widens, deformations are much smaller, plastic failure does not take place, and pavement surface roughness is therefore improved. In addition, shear projections strengthen the contact interaction between the BIAS upper surface and the connecting road materials. This improvement results in a slight increase in structural stiffness and peak force, a considerably enlarged longitudinal deformation zone under push displacement, and enhanced pavement smoothness.