Management of excess water from the pavements and road surfaces, due to rainfall, is not only important for the safety of the traffic but also important for the long life of the road structures. Drainage inlets improperly designed or constructed may lead to an unsafe depth of stormwater on the road surfaces leading to hydroplaning, which may cause the skidding of the vehicles and an increased number of road accidents. As such, the hydraulic behaviour of the most common road drainage inlets was investigated using lab-scale models and the findings are reported in this paper. A rainfall-runoff simulator was used to produce rain of various intensities on the lab-scale roadside drainage system. The main intention was to study the effect of rainfall on the commonly used circular, rectangular, and grated inlets. Rainfall intensity, inflow, water depth on the model road surface, and outflow rates through the inlets were monitored. Experimental results indicated that open rectangular inlets are the best compared to circular and grated inlets, with regards to quickly releasing water from the road surface to the roadside drains. Based on the lab-scale model study, the grated and circular inlets held 64 % and 28% more runoff depth (respectively) on the road surface, compared to that the rectangular inlet. For the same rainfall intensity, a rectangular roadside inlet was found to cause less stagnant water on the road surface.