The size and density of fatigue cracks in orthotropic steel decks (OSDs) progressively increase over their service lifetime, leading to the coupling and merging effects among multiple fatigue cracks (MFCs). However, the growth behavior of spatially interacting cracks remains unclear, making conventional approaches and criteria inadequate for evaluating the fatigue life of MFCs. This study investigated the dynamic evolution of spatially coupled MFCs in OSDs through both numerical and experimental approaches. The MFCs were categorized into collinear and parallel patterns according to their spatial arrangement. Numerical results indicate that the coupling effects between collinear and parallel cracks are different significantly, where the collinear cracks have higher growth rates compared with that of parallel cracks. The stress intensity factor (SIF) at the merging point of collinear cracks increases considerably, resulting in a sharp transition in the crack shape. The shape ratio for different types of cracks eventually converges to 0.26 during the propagation process. MFCs with an initial crack depth of 4 mm achieves a 27.8 % reduction in fatigue life compared to single cracks.