| To investigate lane load disparities and their loading effect characteristics due to the influence of freeway traffic rule of certain vehicle type travelling in certain lane, Weigh in motion (WIM) data from two lane, three lane and four lane unidirectional freeway were adopted as the basis of the study. Vehicle lane choosing probabilities were firstly counted. Traffic volumes and vehicle weights among lanes were then compared. Finally, the influences of lane load disparities on local design of bridge deck system, bridge global design, and bridge fatigue design were analyzed from the corresponding perspectives of extreme truck weight, extreme loading effect and equivalent fatigue stress. Results indicate the vehicle lane choosing probabilities are differential in multi lane roads, and the differences among vehicle composition, traffic volume, and load distribution in lateral lanes are significant. The extrapolated extreme lane truck weights are different to each other, which illustrates a modified lane factor should be considered in the local design of bridge deck system if a unified truck load model is utilized. The ratios of extreme load effects among lateral lanes and those of equivalent fatigue stress are all not equal to 1, which highlights the strength and fatigue effects in lateral lanes under random traffic loading are different to each other, and should be considered into structural optimization of bridge global design and fatigue design.