Bridge structures are exposed to various dynamic loads, traffic loads, wind loads, impact loads, etc. The dynamic effects of possible loads should be taken into account by designing of bridges and during all time of the maintenance. Static and dynamic load tests have frequently been used before the opening of middle and long span bridges to verify the actual structural behaviour compared to analytical analysis. The load carrying capacity of the bridge is usually estimated by empiric calculations, but considering the dynamic loading due to the heavy traffic, the actual deflection and the dynamic properties of the bridge superstructure can be different. Increased stresses in the construction due to the dynamic loading can create cracks due to the fatigue and hence collapse of the structure. In Latvia dynamic tests under special vehicles are standard proof load test before opening the bridge for use. Heavy trucks with controlled parameters are usually used as dynamic loads. The paper analysis the test results obtained during more than 50 years period. The main characteristics obtained from testing are the vertical displacement of the deck including dynamic load factor, the natural frequency of the bridge, the dynamic amplification factor and the logarithmic decrement. The results are compared and relation between dynamic characteristics and bridge properties are determined. The paper presents results obtained from dynamic load tests of bridges. The obtained results showed that the natural frequency highly depend from length of span, statical scheme of bridge, type of span cross-section, structural materials, construction methods, bearing type, etc. There was found that the dynamic amplification factor was not dependent from natural frequencies, but showed dependency from logarithmic decrement. The logarithmic decrement showed dependency from length and types of span structures.