Vertical Subway Concept

One consultant is trying to reduce the amount of leasable space gobbled up by passenger elevators. A 40-year-old concept for a lift that rides on rails, like a vertical subway, is finally ready for prototyping, thanks to recent technological advances—especially in drive systems, said Adrian M. Godwin, chairman of elevator consultant Lerch Bates Ltd., Woking, Surrey, U.K. "A prototype could cost 10 million euros," he said.

In theory, the system takes up 60% less space than a single-deck elevator system and 30% less space than a double-deck system, said Godwin. "We are looking for companies willing to invest in the technology because the business case for adopting these systems in high-rise buildings is overwhelming," he said.

Called Vertrak, the system would enable multiple cars to circulate up and down within adjacent one-way shafts. Cars would rise in the "up" shaft, move across and return via the "down" shaft.

Elevator experts, acknowledging that the system would revolutionize vertical transportation, are wary of the concept. They particularly cite safety concerns related to stopping at high speeds. Godwin said the concerns have been addressed.

After the Vertrak system is prototyped, Godwin hopes to raise money for another prototype: a related system for sloped rail travel. The rail would arc and the cab would hang from it, adjusting to stay vertical, much like a Ferris-wheel cab.

Last month, CTBUH, the world's height-ranking authority, anointed Dubai's 413.4-m-tall Princess Tower, just completed, as the tallest residential building. On deck for the world's second-tallest skyscraper is the 632-m Shanghai Tower, on a course for completion in 2015.

CTBUH predicts Kingdom Tower, set for completion in 2017, will be the world's tallest building in 2020, followed by the Burj Khalifa. Pile work begins this month on the $1.2-billion Kingdom Tower.

For the supertower, the biggest remaining challenge is making sure all parties deliver on time, said Talal Al-Maiman, CEO of Kingdom Real Estate Development Co. "If the project is not controlled in terms of when it will finish, it will make the financials difficult," he said.