A year on, it's still difficult to look on 11 September with any historical perspective. Last weekend's arrest of a suspected Swedish hijacker reminds us that the risk of further atrocities is still present. Nevertheless, we can draw a few conclusions. Some construction firms were genuinely hit by last autumn's cuts – although not as many as pleaded force majeure to explain their dismal 2001 results. The forest of cranes punctuating London's skyline suggests that developers haven't lost faith in towers. And as for the notion of erecting a Star Wars-style forcefield to repel planes from cities, well, we can put that down to post-9/11 delirium.
Lord Foster and others have invested plenty of energy over the past year in restoring public faith in skyscrapers. But tall buildings will become more problematic in the wake of 11 September, and not just because a group of MPs have declared them unnecessary. Insurance premiums for developers and their contractors are rising fast, and increasing demands from tenants for safer structures may start to make costs prohibitive. Designers say that potential occupiers remain apprehensive about moving into iconic towers. This is partly because of the perceived risk of locating all senior staff in one place; nobody wants to become the next Cantor Fitzgerald. But it is partly because of the fears staff now entertain about their chances in an emergency. Will anyone ever return to their desk again, like some victims of the World Trade Centre did? So the MPs who called for maximum evacuation times – no more than 20 minutes, surely – and regular reviews of fire certificates are only echoing public sentiment. Tougher regulations are on their way.
Nobody could have prevented the devastation of the twin towers, even though the engineers did consider the impact of a slow-moving aircraft lost in fog. But could more people have survived under a different design? Possibly. The structural engineer Leslie Robertson admitted as much on Monday's Channel 4 documentary on the attack. And whatever the unique features of the 30-year-old towers, their catastrophic collapse does contain lessons for other designers. The UK's Tall Buildings Working Group has called for wider escape routes; in the twin towers, the stairwells were not only narrow but too close together. Ineffectual fireproofing on the lightweight trusses that supported the floors might also have accelerated the collapse – although the owners denied this – and questions were raised about the flimsy protection of the elevator shafts. Masterplanners, meanwhile, argue that the spaces outside could have given firefighters easier access. More research will be needed before anyone rewrites the rules on skyscrapers. But it would be negligent for anyone to stop trying to learn the lessons of 11 September. There are no more unimaginables.