The use of grooving in the pavement surface is a common approach to improve wet weather skid resistance and reduce hydroplaning risk. Field measurements have found transverse grooves effective in significantly improving skid resistance and reducing the occurrence of hydroplaning. Nevertheless, despite the reported effectiveness of longitudinal grooving in wet weather accident reduction, most experimental studies do not record any significant increase in the measured skid resistance of longitudinally grooved pavements. An analytical study is presented to evaluate the relative effectiveness of the two types of grooving in terms of their ability to reduce hydroplaning potential and their respective skid resistance available at the onset of hydroplaning. The groove dimensions examined cover widths from 2 to 10 mm, depths from 1 to 10 mm, and center-to-center spacing from 5 to 25 mm. It is found that in terms of the ability to raise hydroplaning speeds (i.e., to lower hydroplaning risk) and skid resistance values, transverse grooving consistently produces much better results than longitudinal grooving. The simulation results confirm that, for longitudinal grooving with dimensions within the practical ranges, only marginal improvements occur in both hydroplaning speed and skid resistance in the longitudinal directions. However, an analysis by the simulation model indicates that, unlike a smooth plane surface that has the same skid resistance properties in all directions, longitudinally grooved pavements have significantly higher skid resistance as the skidding direction deviates from the true longitudinal direction. The quantitative simulation analysis suggests that this relationship has the effect of enhancing traction to keep skidding vehicles within the roadway and to cut down on wet-pavement accidents, a result that has been widely observed in field applications of longitudinal grooving.