Curb inlets with extended throat sections - how to create

[dpw-tom]

After reading previous posts, I am still at a loss on how to model a curb inlet with extended throat sections as one inlet/part (i.e. VDOT std DI-3B, -3C in VA where I work) in C3D. 

From the documentation and can do basic inlet modeling.  I am new to the c3d pipes modeling.  Is there a white paper on this topic? If not, if someone has done this type of modeling, could you either 1) give instructions on how to create the part (inlet) and/or 2) share their models?

Thanks