Bridge deck slabs without shear reinforcement under concentrated loads close to line supports may develop different shear failure modes: (i) one-way shear by shear-compression or flexure-shear failure mechanisms and (ii) two-way shear or punching shear under asymmetrical loading conditions. Notably, most publications concentrate on one of the failure modes and do not delve into the transition between these failure modes. This study proposes to discuss the level of precision of the Critical Shear Crack Theory (CSCT) to predict the shear capacity of slabs subjected to transitional failure modes in shear due to asymmetrical load or support conditions. For this purpose, the CSCT models of one-way shear and two-way shear are coupled with Linear Elastic Finite Element Analyses (LEFEA) to evaluate the non-uniform distribution of shear forces and bending moments around the loaded area and on the control sections used. The use of LEFEA aids in understanding the change of failure modes according to parameters such as the member width to effective depth ratio and the shear span. The results indicate that the CSCT coupled with LEFEA allows for accurate predictions of the shear and punching shear capacity of slabs according to the governing failure mode of the tests.