Short track defects cause large dynamic contact forces at the wheel–rail interface, leading to fast deterioration of the track. Early detection of such defects is very important for timely maintenance. The track technical state can be assessed with the aid of axle box acceleration measurements, which can indicate short track defects like squats, welds with poor finishing quality, insulated joints, corrugation, etc. As a first attempt to determine a quantitative relationship between the characteristics of the accelerations and the track defects, axle box acceleration at a squat and a thermite weld were simulated through finite-element modeling. The magnitude and frequency contents of axle box acceleration at squats agreed with measurements. The results for welds had some discrepancies, which were mainly attributed to the fact that the modeled geometry of the weld deviated from the real one.