In typical bridge construction, you will have piers or bents that support the longitudinal, moment carrying members which are usually called beams, girders, joists or stringers depending on the layout and material used. The piers and bents will typically be constructed only in the plane transverse to traffic and will not have connection from one substructure (pier) unit to the next.
A railroad trestle will be comprised entirely of wood and one bent or pier will be dependent on the next with longitudinal and diagonal bracing to support the longitudinal loads. There will be no clear spans between piers.
In other words, in a trestle, all of the piers work together while in typical bridge construction, each of the piers will carry load independently.