Houston Strategies blogger Tory Gattis has an excellent post on the relationship between New Urbanism and mobility. He makes a great point that it's a matter of scale:
I think New Urbanism needs to realize it is a great paradigm at the neighborhood level, but that those neighborhoods need to be linked together with a freeway and arterial network across a larger region if you want an integrated and cohesive metro economy. The pedestrian and the car operate at totally different scales (3mph vs. 30-60mph), and therefore the right form factors for each are different. You don't build a city around just the pedestrian or just the car, but for both. Getting militant about one over the other makes about as much sense as asking "should our country be built around the car or the airplane?" Well, the answer is both: the car for shorter distances, and the airplane for longer ones - and that means interstates and airports. The same logic applies at the scale of a city/metro-region: you need freeways for longer distances, arterials for medium distances, and narrow streets with sidewalks for very short distances (i.e. the pedestrian district/neighborhood). New Urbanism makes the very valid point that we've sort of forgotten about that last category over the last few decades - and we're now rediscovering it - but that doesn't invalidate the other two scales any more than they invalidated the pedestrian scale.
The value of mobility gets lost in a lot of the rhetoric. Mobility is generally defined as the ability to get from point A to an arbitrary point B in minimal time, but the real-world definition for cities is "I'm willing to travel up to X mins for Y activity - what are my options?" That might be 30 mins for work, 15 mins for a restaurant, or an hour for a museum, concert, or sporting event. Mobility means more job opportunities for citizens and potential employees for employers (which translates into upward career mobility and higher productivity as skills better match jobs). Mobility means me or my spouse can take that new job without uprooting my family and moving, which makes for stronger communities and stronger families. Mobility means retail shops and restaurants can draw on a larger pool of customers, therefore supporting more eclectic diversity. Mobility means more access to affordable housing within a reasonable commute. Mobility means I'm more likely to volunteer at a charity or nonprofit, or attend classes at a local college to work part-time towards a degree.
Do yourself a favor and read the whole thing. And be sure to check out Reason's Mobility Project page for more info on our work to develop and implement a framework for removing congestion as an obstacle to mobility.