No one goes there anymore, it's too crowded

Yogi Berra said that.  I also recall someone saying at some conference on smart growth or new urbanism: the more cars sharing the road, the more people get frustrated (hence all the car ads of people driving with no other cars in sight), while the more people on a well designed sidewalk, the more we tend to like it. 

One of my frequent complaints about 3D simulations depicting a new smart growth development or showing off a new transit technology is that they do a horrible job at including LOTS of people in the simulation.  The reason is obvious, it takes a lot of time and skill to add realistic looking moving people around the sidewalks and crosswalks of a streetscape. Futuristic transportation videos often show the highspeed train or Personal Rapid Transit void of people.  It feels like your traveling through a ghost town, and the unintended side-affect is that you end up feeling alone.   Slowly but surely animators are including people walking around simulations.  

Check out this crowd simulation: It's a real time crowd model based on continuum dynamics created by designhive. The motion of crowds is controlled by a dynamic potential field, which allows moving obstacles to begin avoiding each other well in advance without the need of explicit collision avoidance. You can also set up different degrees of discomfort zones (i.e. J walking in front of a car much higher than J walking behind a car, much higher than sticking to the sidewalks and crosswalks).  In this example, the pedestrian and traffic simulation models are combined with a 3D Studio Max model of an Oxford Circus proposal, making a very realistic finished product.  There is a paper and video by Treuille, A. Cooper, S., and Popović, Z, on using continuum dynamics for crowd simulation.

Another technique that works incredibly well (if you're good at it), is to combine video of real street scenes with 3D animation using green screen technology -- a technique now ubiquitous in the movie industry.  Jonathan Arnold with Arnold Imaging in Kansas City Missouri has put together a number of  development simulations using this technique.  Check out the one he did for Kansas City. Cool stuff.