The theoretical correlations have been employed so far in 1D models to estimate train drag inside the tunnel, but verifying their accuracy is essential. This study uses 3D numerical models to compare drag coefficients inside a tunnel with theoretical predictions. Two train models (cubic and realistic) are examined with two uniform and accelerated velocity profiles. Findings demonstrate that the train drag significantly increases at the tunnel entrance. However, the nose and side drag will gradually decrease in the middle and exit of the tunnel, while base drag remains almost constant. Results also show that theoretical model predictions for side drag are acceptable, but there are significant discrepancies in estimating local nose and base drag. The model underestimates the nose drag at the tunnel entrance and overestimates it in the middle and exit, resulting in a lower mean error. For base drag, the model significantly underestimates values during train movement inside the tunnel.