Influence surfaces for consideration of laterally distributed loads, or two-dimensional load trains, can be defined in RM Bridge by defining and assembling a set of parallel influence lines.

The Default is to have the input Surface as an empty variable at the Traffic Lanes definition. This will then not perform any 2D Traffic evaluation with influence surface and the program will perceive the Lane as a usual one, and not as an assembly to be included in any Surface analysis. When there is an input, the Lane Number will be the name of the influence surface to which the influence line belongs.

Note that influence lines combined with an influence surface must have a synchronous arrangement of lane points. The interpolation in the lateral direction doesn't perform a geometric control for orthogonality but uses the corresponding points at the beginning of the different influence lines as interpolation points.  Additional or omitted points at the beginning of a lane can be considered by defining a respective offset, for example, in the case of a skew section at the bridge beginning.

   

Additional information and example can be found at the link below and at the FAQ:

communities.bentley.com/.../rm-bridge-faq-influence-surfaces-example