Bridges are structures that are designed for a service life up to hundred years. During the service life of a bridge the level of the traffic load and intensity rises hence it demands regular bridge inspections to determine the actual load carrying capacity of the structure. However the actual traffic load models significantly differ from the characteristic load models used in the design codes. Analysing the design codes used in Latvia for past twenty years it was found that the design loads on the bridges have doubled since the codes were approved. Therefore the use of the actual traffic load models to assess the load carrying capacity of the in-service bridges can significantly save the maintenance cost. In the past traffic actions had an attribute of a great uncertainty, however with the introduction of Weight-In-Motion systems it is possible to collect vehicle information without interfering the traffic. This includes data such as - number of axles, wheelbase, speed and axle loads which altogether shapes the picture of actual loading range on the roads and bridges. The new traffic load models are derived from results of the Weight-In-Motion systems analysed with a new on probabilistic approach based method. The collected Weight-In-Motion data analysis was performed to obtain load distribution diagrams, determin heaviest axel disposition, traffic speed and intensity values and vehicle weight correlations. This research allowed to develop traffic load models and determin values of the Eurocode load model LM1 calibration factor alpha for bridges with a span length up to 30 meters, considering the characteristic loads on Latvian roads and bridges.