Rail seat deterioration (RSD) is the deterioration of the crosstie concrete underneath the rail that causes track geometry problems and weakens the track structure. RSD may have up to five potential mechanisms, and this research investigates one of them: hydraulic pressure cracking. A laboratory test apparatus and procedure were devised to measure the surface water pressure in a laboratory rail seat using rail pads of differing material composition and surface geometry. A model of the effective stress in a concrete-crosstie rail seat was developed to estimate the water pressures on the rail seat surface and whether they could lead to damaging pore pressures in the concrete. Comparing the effective stress model and the measured surface water pressures, hydraulic pressure cracking appears to be a feasible mechanism for RSD, given the correct combination of high rail seat loads, sufficient moisture, and a rail pad surface that generates high water pressure.