New poster; Apologies -- Text fix and tip of hat to Mr. Crawford
Have a City reference design that will have to move about 30,000 people worst case in an hour and a half at the worst point (near the city center metro stop), at rush hour. There would be separate Pedestrian crossings but would only be as low as ten feet. These passenger transport routes would most likely be five feet below the surrounding pedestrian grade. Low Clearance truck freight , taxis and occasional cars would share the route with the passenger transport system. No Bicycles would be allowed in this depressed grade. The Five foot depression and ten foot ped bridge clearance puts the ped crossing at 6 feet above the surrounding pedestrian grade if there is one foot of structure thickness in the foot bridge This is the minimal grade delta for perceptibly agreeable pedestrian access across such throughways (similar to Venice)..
So what passenger transport system can meet these criteria? Third Rail doesn't allow other vehicles (non-tracked) on the road, does it? Catenary systems need much more overhead clearance don't they? And buses are not as desirable to passengers, are more costly in the long run and can't meet the worst case throughput requirements can they?
Note, that this scenario, I think, will be in a large class of relatively carfree designs and retrofits where J.H. Crawford's a Metro Stop and a *Rail freight line in every district feature's initial cost gets vetoed in favor of a mixed mode distribution that takes a middle point initial vs. sustaining cost approach. And where transit route impacts on Pedestrians are more thoroughly accounted for. Note that Venice, can in fact be a model for a city with car separation, not a truly carfree city in that the little personal motor boats are the cars, the smaller rowed boats (typically Venetian Sandola) are like personal pedicabs, the Gondolas (when used centuries ago) as then public and private pedicabs. The Vaporetti are the bused, etc... The important point is that there are VERY limited parking spaces for these personal cars (motor boats and row boats) in Venice and in my reference designs; after accounting for bus or tram platforms, freight docks, taxi platforms there is almost no parking space for autos. Venice accommodates pedestrians better than any mixed mode city I know of, so a non-water based model should be considered... and accommodated.
BTW, I just LOVE Crawford's reference design, other classes (ie. packed versus isolated districts) just need to be considered. My wife came up with the same basic topology as Mr. Crawford's in a vacuum and we called it the String of Pearls topology. It is more likely to be implemented than any of mine because each early phase district can be put in a low density to empty region of a city; usually in a region of low value-- hence lower cost and greater acceptance by the adjoining neighbors; they are relatively poor so look forward to any improvements to a public xport system they already depend on.