I deal with a lot of urban design projects which involve traffic studies. Often, if a level of service E or F shows up in an alternative for out years (which, aside from the failing LOS, may be good urban design), this alternative is automatically taken off the table. I have a problem with this.
I know how these traffic projections are derived (also akin to knowing how sausage is made), and there are too many unknowns and flimsy variables involved to give me certainty that for X intersection in the year 2030, Y number of cars will travel through it causing Z delay. Traffic is more self regulating than we give it credit for (see Anthony Downs), and in applying fluid dynamics to human behavior, I think we water down both sciences into something more half-assed.
I'm interested to hear other people's thoughts on this and also rationales that can give me more faith in traffic models.