Large station footprints (covered earlier) pose a particular problem for surface transit modes with wide geometries: as with the expressway-interchange station I ridiculed then, the infrastructure grows to a scale so large that it dwarfs pedestrian circulation to/from the station.
Wide geometries particularly hurt the utility of water taxis, which rarely prove truly practical in modern cities. Boats have very wide geometries and require deep-water docks far from shore, usually half of the walk shed is wasted on water, and high-intensity land uses and high-capacity transportation connections are usually set far back from flood-prone shorelines. Thus, even North America’s busiest transit ferry (Vancouver’s SeaBus) is separated from the street by 300m (~1000′) of walkways:
Thus, the ferry’s 400m/five-minute walk shed is limited to just one block beyond the station itself:
David Alpert recently suggested Vancouver-style ferries along the Anacostia, but the geometries of both the ferries and the waterways make this difficult. Even though I probably live closer to a water taxi dock than just about anyone else in D.C., I have yet to come up with an occasion to take the existing water taxi service — it’s super slow and doesn’t go anywhere useful.
Because of Greenleaf Point (Ft. McNair) and Hains Point, the distances between the docks are much further via water than they are via land: the Wharf has an enticing waterfront, but it’s on the nautical equivalent of a cul-de-sac, 1.5+ miles away from the main stem of the Potomac. Thus, Wharf-Georgetown is twice the distance by water as by land, and thus it’s much faster to walk or bike between all of the water taxi stops. Even once riverfront sites like Buzzard Point, Poplar Point, and Reservation 13 get developed, the Anacostia Riverwalk Trail will be much more important as a mode of transit: it’s that much closer to land-side destinations, and available on-demand, 24 hours a day.
Ferries are slow compared to land travel: 30 MPH is “fast” in nautical terms, and 40 MPH is “high speed.” Thus, 1.5 miles means a 10-minute roundtrip time penalty just to get up to the dock, plus the not-inconsequential time spent actually docking. Ferries are surprisingly fuel-inefficient, since water displacement sucks up a lot of forward momentum.
What’s more, the landside transportation capacity isn’t really there most anywhere along local rivers. The walk shed from any ferry extends only 1-2 blocks inland (see the 400m walk sheds from Georgetown waterfront and Kennedy Center docks), and along most of the Potomac or Anacostia that space is taken up by highways, parkland (in the shallow tidal rivers), or steep hills (in the Potomac Gorge north of Roosevelt Island). Even in Alexandria, the quintessential port town, and at National Harbor, most of the activities and transport connections are set well back from shore. Just because a lot of things exist vaguely near the Potomac doesn’t matter, if the last-quarter-mile connections are awful. Already, we have lots of local examples of under-used transit that gets you sort of close to things, but not door-to-door.
Water taxis come closer to being time-competitive in situations like in Chicago, where land traffic congestion is appreciable and major activity centers like the railroad stations are within 200′ of the river — but where the river usually sits well below the (elevated) level of the streets around it. I’m hard-pressed to find many other examples in the USA where similar conditions exist, though.