Sunday, March 27, 2011

SLC Frequent Network

Salt Lake City's 'Frequent Network' (15 minutes or less between vehicles) is oddly distributed. N-S routes through SLC include Trax, the 203, the 205, the 209, 213, and the 220. E-W routes would be the 2, Trax, and.... 21, at 2100 S. So between Trax at 4th South, and the 2100 S., there is no frequent E-W service. Both the 9 and the 17 run at 30 minute headway, and include a baffling detour (a topic for a later post). It's a strange absence, given that the street grid is still largely intact in that area.  Closer examination of the street-grid explains the lack--Liberty Park obstructs any potential E-W route from 9th to 13th, and any route between 13th and 21st would have to pick its way through an off-set grid.

1300 South is certainly a through street, so the total lack of any bus service along it is certainly puzzling. The brutal hill between 1100 E. and 1500 E. may be the explanation for that--it is very difficult to safely load and unload a wheelchair on a 20 degree slope.

Tuesday, March 1, 2011

Low Rise, High Density

Looking at images of Paris and New York's Lower East Side, I realize that very dense, older urban areas are not particularly high rise. In many cases, they fail to exceed 4-5 stories. But I would estimate a Floor Area Ratio of something like 400%, which generates transit suitable densities. What is critical in generating sufficient density for transit appears not to be tall buildings, but the lack of parking. Every car takes up 300 square feet per parking stall. Include landscaping and access lanes, that means 10 acres of land only provides about 900 parking spaces. Keeping that same ratio, a 1 acre parcel could be used to produce 90 surface parking lots. Or (at 350 ft^2) about 125 small offices. But if each office is matched to a parking stall, so the net production is about 62 offices.

Structure parking is enormously expensive, because it has to support a 'live load' of cars, rather than people. Thus, as much as possible of the need for parking will be met using surface lots. Assuming a 1:1 office:parking ratio, 2 stories of office mean that 2/3 of the parcel must be devoted to surface parking. With a four story building, 80% of the lot will need to be devoted to parking. Automotive oriented high density will produce a city of vast towers, islands in a sea of parking--hardly urban.

Thus, generating urbanism is not just a matter of generating density--it is a matter of providing density without providing parking. Which means alternative modes of access.