Pittsburgh Main Thoroughfares and the Down Town District / Improvements Necessary to Meet the City's Present and Future Needs

by Frederick Law Olmsted

Section showing one type of hillside street

There are two special forms of street, developed here and there in hilly cities all over the world, of which Pittsburgh needs to take account in its suburban development. In many instances, and for long distances, existing suburban thoroughfares that must be enlarged and improved, and others that must be laid out, are compelled to run along the face of hills so steep that a street of level cross section, even though limited to 80 feet, would leave the land on one or both sides so far above or below the grade as to destroy its value for building purposes. In such cases it is often practicable to make use of one-sided streets or two-level streets. The former are designed to give accessible frontage on one side only, usually the uphill 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. 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.

Section of a two-level street at Zurich, Switzerland.

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 ultimately to convert it into an ample urban thoroughfare with the minimum of cost and inconvenience.

Widening Old Streets

Whatever radical changes may be made to improve the present or safeguard the future condition of the thoroughfare system in regions that are now rural, there remains a huge problem within the district where the street system has already crystallized into substantially its final form. Here increased capacity can, for the most part, be secured only by local improvements and widenings of existing thoroughfares.

Fortunately, the building up of the street frontage with solid blocks of stores, apartments, and business structures, has at most points followed rather slowly after the earlier wave of detached dwelling houses, and a large proportion of the streets which are destined to be the main arteries of the huge future city are still lined by buildings which are set back at various distances from the street, leaving front dooryards between them and the sidewalk. Outside of the down town district, and a limited area in East Liberty, it is possible, therefore, to provide for the ultimate widening of these streets without the destruction of many valuable structures, provided the preliminary steps are promptly taken.

As traffic increases and the lots come to be used for business purposes, such a set-back becomes inconvenient and undesirable, and one by one the buildings are either extended to the sidewalk by new additions, or new buildings are erected on the sidewalk line. The reason for this change is not usually that additional lot depth is required, for often considerable yards are left unoccupied at the rear, but is simply that on a commercial street the buildings need to be as close to the stream of traffic as possible; and since the individual lot owner cannot move the street as a whole up to his building, he has to extend or move his building to the street. His immediate purpose is thus served, and ultimately the whole row of buildings is similarly advanced in response to changed conditions. But at just about the time when this process is fully completed, the volume of traffic flowing over the street is apt to have become so great that everybody recognizes the street to be too narrow for the increased traffic it has now to carry. If the case is a bad one, the inconvenience due to overcrowding the traveled way will in time reach a point where, in spite of the great cost of such an operation, the buildings all along one or both sides of the street have to be destroyed and a new building line established—it may be on the very line where most of the original buildings stood before increasing traffic began to offer inducements to move them forward to the sidewalk. Indeed, it may be said as a general rule that on any street where the buildings are set back from the sidewalk line the very advancement of a few buildings to the sidewalk line is a sign which points directly to the growth of travel and indicates that ample width will soon be needed in that thoroughfare.