This research was done as part of a long term project, with the goal to monitor multiple bridges over an extended period of time. Due to the nation’s aging infrastructure and the limited amount of funds to upgrade and maintain it, structural health monitoring (SHM) is very important because it provides in depth information about a structure to be used in decision making. SHM of bridges includes monitoring the effects of traffic loads. This paper discusses the development of a bridge weigh-in-motion (B-WIM) technique that uses the rainflow counting of strain cycles. Typical B-WIM techniques have proven to be accurate but require large algorithms and gauges at multiple locations across the span, and the strain gauge temperature drift must be accounted for. The rainflow B-WIM (RF-BWIM) decreases the processing of the B-WIM and automatically accounts for drift, thus allowing temperature and other analyses of the same bridge to be possible. RF-BWIM also has the potential to decrease the number of sensors required. Strain data taken from an existing long term monitoring system was used to develop the RF-BWIM. The development of the RF-BWIM, as well as a method to determine a virtual gross vehicle weight (C-GVW) used in calculating the RF-BWIM output, is presented.