So here we go.
Yes, I live along City Line Avenue, and like locals near and far I know there's always a Line in City Line, official designations to hell. The current state of City Line is a weird sort of urban-suburban mishmash. It's got beautiful and not-so-beautiful garden apartments, but at the same time it's got a totally autocentric assortment of '50s-'80s office parks and strip malls, the youngest of which is a power center with a Target. It's still got Philly's Saks, but the luxe quotient is going down, and has for some time: since, in fact, King of Prussia went upmarket in the late '80s and attracted Neiman Marcus and Nordstrom over a hapless center city. And with Route 1 being a primary funnel from parts Main Line way to the Schuylkill Expressway, it's a traffic nightmare.
But it could be special. It's a key link. It lies between the Ridge Avenue string of Manayunk, East Falls, and Roxborough, and the heart of the Main Line strung along Lancaster Pike, from Overbrook through Wynnewood, Ardmore, and Haverford towards Bryn Mawr (with 'Nova lying just beyond). Bala village lies just off it: an immaculately preserved commercial heart. Its communities, both urban and suburban, are exceptional in character and quality; even Wynnefield's urban heart deserves investing in. It is, in short, a perfect link for reurbanization.
City Line Avenue was never a perfect form of a suburban strip, the way e.g. Bethlehem Pike in Montgomeryville or Old Lincoln Pike in Langhorne are. Urban nodes have always existed around Overbrook and Bala stations. This offers bones for reurbanization. It has the three components of life--residents, jobs, and wares--and so offers a strong framework for densification.
How to do it? 1. It is the city line. A unified zoning code along both sides will aid efforts to reurbanize. 2. Impose a height limit--nothing too strict, but enough to ensure that megalomania for height doesn't take precedence over infill. 80 ft. (that's eight stories!) should be plenty. 3. Pay attention to the street. The avenue is the heart, and axis, of urbanization. To do it right, the avenue--on the surface--needs to provide access and movement for all forms of transportation, in a comfortable fashion. Extending a trolley line from 69th St. here (and beyond?) will help cement the district's newfound importance. And: 4. Get rid of excessive parking!
Property line to property line, the avenue varies between 80 and 130 ft. It's at its widest as it's dropping down the hill towards the Schuylkill. Normally, the width from sidewalk to sidewalk is just 85 ft. But the carriageway has four 11.25-ft through lanes and a 15-ft center turning lane, making it alone 60 ft. wide. For the carriageway, we want 4 10 ft-wide traffic lanes* and a reserved 20-ft transit median for light rail. (If the median need be wider, the through lanes can be narrowed to as little as 8.5 ft., perhaps.) Along the sides we want (a) a nice deep sidewalk (say 10 ft.), (b) a bike path on at least one side, and (c) some nice street trees, possibly in their own planting strip.
This is where the problematics come in. We can't narrow the traffic lanes any further, unless one wants to provide a completely segregated traffic or transit passage**, and so we've got to share something. We want the light rail to go fast and not be stuck idling at lights, so sharing through lanes with it is out; we've already road-dieted the through lanes as far as we can sanely go. We will thus have to integrate pedestrian and bike passage at those points of greatest compression (where the road is narrower).
We do not want any takings which involve demolition. This is wasteful. Minor takings of obsolescent setbacks, mostly in the form of small parking lots, may be useful for providing space for a full bike track. Another possibility is to create a pinch point where the road is narrowest, at 54th and City Line, which includes some preservation-worthy ca. 1920s structures as well as a large dorm (Lannon^ Hall) and some more recent rather forgettable constructions which are nevertheless part of St. Joe's campus^^.
So--where the road is narrowest, at 80 ft., we'll have 40 ft. of road lanes, a 20 ft. light rail line, and two 10 ft. sidewalks with trees in planters^^^. When we have 90 ft., we'll add at ten-ft, two lane physically separated cycle track to one side (likely the City side: the setbacks there aren't broad enough to be subdivided into building plots). And finally, at 100 ft., we can have the trees in their own green strip rather than planters. The trees, we'll assume, are London Plane or some such with nice deep root systems which will make maintenance easy.
This is, however, just the look of an urban boulevard. Next time I think about this we'll talk about urbanizing the existing built form.
* What, you want to halve the lane count--are you mad? City Line already sees an AADT of, as far as I can tell, ~80k (or 20k/lane). That's a lot. Yes, the light rail should help reduce that, but we're going to still have to assume an AADT of 60k+. The narrower lanes actually slow traffic down some; this will also increase total road capacity by an incidental amount. If you still don't like it, I've got a shiny but über-expensive expressway tunnel option.
** Either a subway or an el, read. Certainly the full buildout could take one; judging by bus congestion, it could even today. But such options are very expensive, and there isn't a network to tie it into at the moment--although one would exist under Philadelphia2050.
^ Née Borgia Hall. It was renamed over the summer.
^^ A bigger administrative building holding these offices would be a wise move, as would another large dorm in the space freed up.
^^^ Since where the road is narrowest also happens to be by St. Joe's campus, we can also have the cycle path veer off into it for a while.