H0 modular bridge.
Please take note that the "whole file" is not intended for printing and it serves its purpose showing how the bridge should be assemblied.
It's composed of a "start section", which should be the extremities of the bridge itself, and a central part. Both the start and central sections have a base and two sides
Please be aware of the fact that you should print a number of upper parts in relation to the desired length of the bridge. That is to say, you always need to print a number of upper parts equaling the sum of starts and central part, minus two. (e.g. in the whole file, you have two start and two central section, so it's a total of 4. As you can see, you have only two upper part, which i chose to be both two start upper part, because they are intended to be the terminal section of the bridge cover)

The modules measure 45 mm in lenght each. You can combine them as they are, or you can bring the files to an editor like tinkercad and elongate the central parts to suit your needs.

Note that there are some grooves in the upper part of the bases, they are intended to connect the modules via joint (see joint file) or via simple glue filling.

It's advisable to verify if the plastic used assures the structural resistance needed to support transiting trains. if it bends, you can put a small balsa wood sustain under the base part.