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usually the up-hill side. The property on the opposite side is reached by the next street, which is laid out correspondingly nearer in order not to make the lots too deep. The width of such a one-sided street may be curtailed without reducing its thoroughfare capacity because it is freed from local business all along one side.

Section showing one type of hillside street

Bluff Street, though not a thoroughfare, is an excellent Pittsburgh example of the one-sided street, and illustrates the great attractiveness which such streets often possess. In a two-level street a longitudinal bank, or retaining wall, is introduced in the middle so as to adapt it to the topography and bring each half of it nearer to the natural surface where the abutting property fronts upon it. Such a street must normally be wider than a single thoroughfare of the same capacity, the saving in construction and in the development of abutting land more than counterbalancing the cost of extra width.

Widths for outlying thoroughfares in a district like Pittsburgh, therefore, cannot be determined by any general rule. Each must be laid out as a problem by itself, the principal objects in each problem being to select a tolerably direct line on reasonable gradient and so to fix the side lines of the location that it shall be possible to meet the immediate needs by constructing an economical suburban road, where it does not already exist, and

Section of a two-level street at Zurich, Switzerland

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Last modified on 22-Dec 1999
Design format: copyright 1997-1999 Bruce S. Cridlebaugh
Original document: Frederick Law Olmsted, 1910