In the immediate aftermath of the 9/11 attacks, public sentiment -- as reflected in CNN, USA Today, Gallup and other polls -- widely held that the fallen Twin Towers should be reconstructed. As planning got underway in 2002, rebuilding officials declared it would be impossible to reposition twin skyscrapers outside the preserved footprints of the original towers. The Lower Manhattan Development Corporation had mandated that Greenwich Street, an important north-south corridor, be reopened through the World Trade Center's "superblock," limiting possibilities for configuring buildings around the thoroughfare and memorial quadrant.

Rebuilding the Twin Towers is not simply a matter of repositioning two 1-acre footprints elsewhere on a 16-acre site. Rather, it is a complex negotiation of transit infrastructure, mechanical and life-safety utilities, street grids and memorial space. A direct northward or eastward shift of the towers would re-shutter Greenwich Street and force at least one tower to straddle a wide swath of potentially terrorism-vulnerable subway tracks. However, with a northeast shift and a slight bend in Greenwich Street, the towers could be centrally situated to the subway and vehicular transit arteries without dangerously overlapping them. The vertical massing of the office space would effectively restore the commercial capacity and skyline lost on 9/11, while providing a prominent corner for an above-ground transit terminal and two large plots for world-class cultural institutions. 

By far, the greatest planning challenge confronting Ground Zero is the integration of its commercial superstructure with the below-grade transit and utility infrastructure. In addition to provisions for cooling plants, air and water intake systems, electrical/telecommunications conduits, and parking, the substructure must accommodate three separate train lines operating at different elevations, with boarding/egress platforms sandwiched between five basement levels. Further compounding this logistical difficulty is that fact that non-transit utilities must circumvent the memorial quadrant, which the 9/11 families demanded be preserved (undeveloped) down to the site's bedrock level.

These parameters necessarily dictate that the commercial and cultural buildings house parking and utility infrastructure while straddling the train lines (which, in turn, must be connected by a central terminal). While intricate, they are far from insurmountable constraints. However, after factoring in security considerations, they leave little planning flexibility regarding the option to rebuild the Twin Towers. After the 1993 parking garage bombing at the World Trade Center and the horrific attacks of 9/11, there is an unacceptable risk in situating parking spaces in -- or allowing public transportation to pass through -- the foundations of any occupied commercial building at this site.

Were the Twin Towers to be resurrected in their diagonally-offset orientation, there is a singular site configuration that simultaneously would restore the former commercial space, require neither parking facilities nor transit arteries to pass through the towers' structural foundations AND avoid creating utility infrastructure within the memorial quadrant.
Rendering of the Libeskind master plan, featuring the fourth iteration ("Windmill" version) of the Freedom Tower Photoillustration alternatively featuring the 'Standing Tall' configuration in the same framing and context

With the commercial office towers confined to the site's northeast quadrant, at least two buildings housing memorial and/or cultural institutions on the remaining land could utilize cutting-edge design by the world's most famous architects. Though the public was overall lukewarm toward the concept of a "haute architecture" master plan, the publicity surrounding the competition spawned a new popular awareness of architecture. As a concrete illustration of a win-win development scheme (one in which the desires of the Arts community to see an architecturally ambitious design could be reconciled with the commercial, memorial and infrastructure demands on the site) the signature rendering above provides for the peripheral site buildings to be designed by the top three vote-getters from the Innovative Design Study: Sir Norman Foster, Rafael Viñoly, and Daniel Libeskind.

For example, Foster, a master at creating one-of-a-kind glass high-rises, could tackle the south annex tower -- the southernmost WTC building in the rendering -- that would occupy the site of the demolished 130 Liberty Street. The rendering above currently features a never-before-attempted opera house design composed of insulated glass tubes, which Innovative Design Study finalist Rafael Viñoly once envisioned for Oslo, Norway. Viñoly could, of course, design an entirely new structure from scratch, but the New York City Opera had expressed an interest in moving to the trade center site. Libeskind -- who built his reputation on wrenching, emotionally-imbued memorial museums -- could design a 9/11 museum for the southeastern plot (much of which is obscured in the rendering by the south annex tower).* 

In January 2004, approximately 14 months after the media publicized the "Standing Tall" land-use study, rebuilding officials selected Spanish architect Santiago Calatrava, one of the world's most famous architects, to design a new transit station at the World Trade Center. The station, intended to connect all of downtown's train lines in a "superhub," became an instant landmark and won the only universal praise of any new structure planned at the site. As it relates to the "Standing Tall" configuration, this development was after the fact, however it is worth noting that the station theoretically would bring the number of "starchitect"-designed buildings at Ground Zero to four.

NOTE: As no two Foster towers have yet been alike, it would be impossible to speculate on his WTC design, and therefore the southern annex tower in the rendering has not been illustrated as a Foster design.
THE SIGNATURE DECONSTRUCTIVIST ARCHITECTURE OF DANIEL LIBESKIND'S MUSEUMS VIÑOLY'S UNBUILT PROPOSAL FOR OSLO'S OPERA HOUSE, WHOSE MAIN BUILDING WOULD FIT THE GROUND ZERO PLOT DESIGNATED FOR A CULTURAL INSTITUTION UNDER THE 'STANDING TALL' CONFIGURATION
RENDERINGS OF SANTIAGO CALATRAVA'S PLANNED WTC PATH/TRANSIT STATION
SIR NORMAN FOSTER'S UNIQUELY DIFFERING TOWERS (from left): THE HSBC CENTER IN HONG KONG, SWISS RE HEADQUARTERS IN LONDON, AND THE HEARST TOWER IN NEW YORK CITY
German sculptor Fritz Koenig's "The Sphere," which sat atop a fountain in the central plaza between the Twin Towers, was one of two major surviving remnants of the World Trade Center. In addition to the seven-story scrap of the North Tower's facade, which became known as "The Shroud," the 9/11 families labeled it an "artifact" and requested that both pieces be a part of any memorial at the rebuilt complex. While the "Standing Tall" configuration would permit both elements to be incorporated into the memorial quadrant, it also would afford the option of placing "The Sphere" exactly to the inch where it originally stood. After viewing its present condition, some visitors might consider such placement a poignant metaphor for America after the attacks: Bruised and battered, but retaining its overall integrity, never uprooted from its foundations or moved from its place in the world. 
"THE SPHERE," SHOWN IN THE PLAZA BETWEEN THE TWIN TOWERS (left) AND AT ITS TEMPORARY MEMORIAL PLOT IN BATTERY PARK, NEAR GROUND ZERO (right).

WTC SATELLITE PHOTOS BEFORE (left) & AFTER* (right)
*At the time the "After" photoillustration was produced, official plans called for partially submerging the West Street traffic lanes below ground along the western border of the WTC site. The image displays greenery covering  these  lanes, reflecting the implementation of the traffic corridor submersion. That aspect of the redevelopment has since been abandoned; although the greenery would thus not extend as far west in practice, the positioning of the buildings as shown in the image would be unaffected and remains accurate. 
For the purposes of this study, the quadrant formerly occupied by the Twin Towers was left as an undifferentiated green space; the decision as to the appropriate 9/11 tribute was left to the victims' family members and appropriate memorial committees. With this infrastructure configuration, parking and utility systems for the complex would underlie only the northwest and southeast corners of the site, allowing the memorial (at the southwest quadrant) to be constructed either at the open bedrock level of Ground Zero or at street grade. Both options would leave the original tower footprints free of any new encumbering structures.
The Standing Tall land-use study situates the main WTC transit terminal at the site's northeast corner, where the station would serve as a functional and aesthetic (above ground) gateway to the complex. A mezzanine spanning from the station entrance to the slurry wall underlying Greenwich Street would create a level concourse with access to the PATH, 1/9, 2/3 and N/R/Q/W train lines, while providing authorized commercial tenants with direct entry into the office towers. An additional access point would connect the concourse level with the new Greenwich Street park created by Silverstein Properties, providing front-door transit access to the new off-site 7 WTC tower. Parking would be self-contained below the cultural buildings at the northwest and southeast corners without intruding on the high-pedestrian-density commercial structures and train platforms, while the towers would carefully nestle between the enclosed train tunnels, rather than atop them. This intricate arrangement satisfies the security, master planning and real estate economic (transit accessibility) concerns that are central to a responsible development program. 

3-D RENDERING OF UNDERGROUND INFRASTRUCTURE