OpenBridge Modeler uses "Solids" extensively in creating accurate bridge models. Solids are used for everything from decks, barriers, segmental bridges to box-girder bridge decks amongst others. Note that several of these elements could end up being long elements. As such it is important to specify the Solids Area accurately before you start placing any bridge elements into the design file. Note that changing the Solids Area at a later time could lead to unexpected behavior and corruption of files.
If you use the seed files shipped with OBM you will see that they have the following settings which are a good starting point
Units
Resolution
Solids Area
Imperial
10000
10 Miles
Metric
10 Kilometers
Starting with the next release of OBM, we will introduce warning messages to guide the user to pay attention to these settings.