The original design did not take into account such a collapse, and so people in the streets were not sheltered from falling debris and ash. Pedestrian safety was not fully considered in this large of a disaster. The several pedestrian bridges which connected Battery Park were completely destroyed, which made it difficult for rescue personnel to evacuate, as well as causing "residents of Battery Park City to have no easy means to reach their homes," (WINDS 2). Yet, the collapse internally rather than sideways did save many more lives from being taken that day. The design did fare well with the protection of the subways underneath the twin towers. The subway system below remained structurally intact, but was severely damaged by flooding, leading to its need to be completely replaced, "The two tunnels to New jersey were flooded from broken sewer and water main, as well as from firefighters' months-long effort to put out fires in the rubble," (Moore 1). Flood damage is much easier to deal with than a complete structural collapse. In the aftermath of this tragedy, many architects and engineers are learning valuable lessons from the collapse of the twin towers. Modern designs feature "Safety features such as fire retarding materials and sprinkler systems help to contain fires, help extinguish flames, or prevent steel from being exposed to excessively high temperatures," (Wilkinson 1). Designers are now also taking into consideration Egress Systems within the structure of their designs. Egress Systems are the "redundancy of systems and robustness in the face of impact by a foreign object," (Mellon 1). Improved communication systems between fire and...

Additionally, redundant evacuation systems such as an "emergency tunnel could be built vertically into the next generation of skyscrapers with appropriately designed redundant elevation systems," (Buyukozturk & Ulm 1). All of these lessons learned will help improve the integrity of future structures, so that a revision of the tragedy of 9/11 will be less likely and more lives will be saved by the design of a building itself.
Works Cited

Buyukozturk, Oral & Ulm, Franz-Josef. "World Trade Center Collapse Assessing the Events." Civil and Environmental Engineering at MIT. Retrieved 23 Sep 2009 at http://web.mit.edu/civenv/html/people/alumni_newsletters/sept_11/index.html

PBS Online. "Building Big: World Trade Center." Building Big. PBS.org. Retrieved 23 Sep 2009 at http://www.pbs.org/wgbh/buildingbig/wonder/structure/world_trade.html.

Mellon. Raymond T. "The Construction Standard of Care after 9/11." Zeltin & De Chiara. 2007. Retrieved 23 Sep 2009 at http://www.zdlaw.com/enews/rtm-security.php

Moore, Martha T. "Quiet Since 9/11, Subway to WTC resumes Sunday." USA Today. 2003. Retrieved 23 Sep 2009 at http://www.usatoday.com/news/sept11/2003-11-19-wtc-subway_x.htm.

Wilkinson, Tom. "World Trade Center-Some Engineering Aspects." The University of Sydney. 2001. Retrieved 23 Sep 2009 at http://www.civil.usyd.edu.au/wtc.shtml

WINDS. "Word at the World Trade Center Involves the Firm's Top Personnel." LiRO at Ground Zero. 2001. Retrieved 23 Sep 2009 at http://www.apfn.org/pdf/lironews.pdf