Timber bridges are still commonly used by several North American railroads. For short spans, they offer an attractive alternative to other types of bridges, as they are economical, faster to construct, and easy to maintain. Current design practices do not allow an independent consideration of the effects of the dynamic loads in sizing the bridge components, because very little information is available on the subject. Dynamic tests were carried out at two timber railroad bridge sites under the passage of trains at speeds varying from crawl, i.e., 1.6 km/h (1 mph), to 80.5 km/h (50 mph). The loads at wheel–rail interfaces, the vertical displacements, and the accelerations were measured at several locations on the bridge spans, the bridge approaches, and the normal track sections. The maximum values of the dynamic load factors obtained were 1.50, 1.65, and 1.85 for bridge, bridge approach, and normal track, respectively; and the corresponding maximum values of the dynamic displacement factors obtained were 1.30, 1.00, and 1.20. The main objective of this paper is to describe the experimental work and the influence on the measured values of the train speed and other factors.Key words: railroad, timber, bridge, wheel–rail interfaces, load, deflection, frequency, load factor, dynamic displacement, track modulus.