San Jose Affordabilty Gap

The supply of land is limited. If you keep all your increasingly valuable land to existing structures, the price of those structures goes insane. Keeping homes affordable means reducing the amount of land per home. San Jose gasped and clutched its pearls, Prop 13 protected homeowners from economic incentives to sell, and now the whole state's housing market is a disaster area. If you want house prices to get sane again, you'll have to build enough rental units that the price-premium for housing makes renting the preferred option, and only those aspiring to build equity through homeownership actually buy houses.

There is a movement afoot to blame income inequality for this, and it undeniably plays a role--when you use price to ration the supply of something (like houses), the people with the most money buy them. And when you artificially constrain your house value assessment via madness like Prop 13, they have zero incentive to ever sell them--a couple of days of AirBnB annually to pay the taxes.

Transportation regime shift

Transportation-wise, road/rail isn't either/or but rather an "and/also". Past a certain point, a central place can no longer boost/sustain its accessibility with cars alone and has to add rail. But that shift doesn't happen everywhere at once, and when you've got a regional governance structure, it takes a long time before it reaches a supporting political plurality. At first, the shift in the transportation regime only affects the most central areas, but over time it ripples outward.

Parking at the periphery

"But where will people park?"  Public garage/lot at end of street--so there should be minimal automobile pass through traffic, and what does pass through will be slowed by geometric design - curb bump-outs all over.

Every bit of walkable urbanism follows the same pattern - parking at the periphery. High Street in Morgantown WV, Shepherdstown WV, Sugarhouse UT, 25 Street Ogden UT, Silver Spring, MD, Pike and Rose in Bethesda, MD, Cary NC. If you want an intact street wall people like to walk along, you've got to put the main parking someplace else--behind the buildings, at the end of the street, in a garage. (Parking tucked under buildings is the preserve of CBD-adjacent areas with high-rise offices).

We've known since Appleyard (pere) that wide streets and heavy traffic limit people's ability to cross the street reflects the friction of crossing is such that the far side of the street is functionally further away. So if you want agglomeration economies of having the things across the street be close, street design needs to reflect it. Any landlord or developer that aspires to have a destination location rather than convenience-oriented strip-retail needs to understand this. Anyone who aspires to TOD needs to understand this. Mall developers understand this.

Because enclosed malls are so auto-dependent, it's easy to miss that they are the original 'pedestrian pocket' of walkable urbanism. Despite the higher cost of enclosure (and heating/cooling all the space), they have become the prime retail location, and no small part of that is because they satisfy the demand for walkable urbanism. Agglomeration economies certainly play a role, but the form matters. Flipping an enclosed mall (stores around a sea of parking) destroys the agglomeration economy--no one is going to walk from one side of the ring, through the parking lot, to visit something on the far side. Even the enclosed mall's 'junior' form -- the lifestyle center--a walkable pedestrian-oriented center strip with stores on both sides, with a parking garage on one end.

Always the same pattern--pedestrian pocket wrapped in retail, with the automobile (largely) exiled to the periphery.

Origin density at transit stations

Origins tend to be rather more spread out, and it requires pretty high density to generate more riders than a Park-and-Ride, which generates one rider per 400 SF. A three-story apartment is actually worse than a Park-and-Ride--not everyone in those apartments will take transit, and parking + landscaping will take up over two thirds of the parcel.  A 2-3 acre bus depot will likewise collect more riders than a garden apartment. So making a fuss about the density of origins near a transit station is rarely worthwhile across most of America. 

Further, origins highly concentrated on a small fraction of land parcels, and highly concentrated on buildings located within those parcels. As getting places requires getting to the front door, it's that access that matters for transit supportive density, while most origin destination calculations are made using metrics like units per acre. Pure geographic coverage is a terrible metric for access--most of the land is empty or occupied by things like private yards. 

Transit supportive density is a bit of a red herring

"Transit supportive density" is a bit of a red herring. The Utah Transit Authority build a very successful transit system by destinations where parking was expensive to build (downtown, universities & colleges, hospitals) and using a mix of PnR and transit centers to aggregate origins. So for making transit work, what really matters is destination density--how much stuff is within a walkable distance (10m) of the transit station? 

TOD > Missing Middle

Using public transit to fix car-dependence is a failing strategy. Providing marginal transportation to marginalized groups (teenagers, people with disabilities, older seniors) is at best a band-aid and at worst a sop. Further, no level of public transit provision will ever be able to fully replace automobility. Hence, undoing car dependence is largely a land-use problem: allowing the magic of density and mixed use to shorten trip distances and enable non-auto modes. Since most of the magic in transportation shifts happens at a pretty high threshold, it's key to focus on land uses in a small portion of critical places. From a transportation perspective, enabling good TOD at a few places beats enabling Missing Middle everywhere.

Not to say that the Missing Middle doesn't matter. Most of America is caught on the threshold where the densest multifamily that's financially viable is the 3-story 'garden' apartment with a huge parking lot, such that until land prices rise to a level where 'wrap' apartments with structured parking become viable, almost no new apartments get built--rather, more and more 3-story apartments get built, just at increasingly peripheral locations.