As cities grow denser and skylines push ever higher, the vertical transportation systems that serve these mega-structures must evolve. Elevators are no longer just a convenience—they are a critical component of a building’s functionality, safety, and passenger experience. Two key innovations—double-deck elevators and sky lobbies—have emerged as cornerstones of modern high-rise design, enabling architects to reach new heights while maintaining efficiency. These technologies, combined with emerging digital and mechanical advances, are reshaping the future of elevator technology in skyscrapers.

Double-Deck Elevators: Stacked Capacity, Shaft Savings

A double-deck elevator consists of two passenger cabins mounted one above the other within a single hoistway. Each cabin serves a different floor simultaneously—the lower cabin stops at even-numbered floors, for example, while the upper cabin stops at odd-numbered floors. This configuration effectively doubles the carrying capacity of each shaft without requiring additional space.

How Double-Deck Elevators Work

Mechanically, double-deck elevators share a common hoisting system—a single set of steel ropes or belts attached to the top of the upper cab, with the lower cab suspended directly beneath. A counterweight sits on the opposite side of the sheave, balancing the combined weight of both cabs. Modern double-deck systems often use separate landing doors at each floor to preserve the safety zone between the cabs and the building structure. The doors must synchronize precisely: both cabs open at their respective floors at the same time, allowing passengers to enter and exit without delay.

Usually, the two cabs are not independent—they move together as a unit. However, some advanced designs allow for a variable spacing between the cabs to accommodate floors with different ceiling heights, though this adds mechanical complexity. The most common configuration is fixed spacing, used in buildings where floor heights are uniform.

Advantages of Double-Deck Elevators

  • Increased Passenger Throughput: By carrying twice as many people per trip, double-deck systems reduce waiting times significantly in high-traffic towers.
  • Space Efficiency: Each double-deck shaft replaces two single-deck shafts, freeing up valuable floor area that can be leased or used for amenities. In a typical office tower, this can amount to thousands of square feet.
  • Reduced Core Size: Fewer shafts mean a smaller building core, allowing for larger floor plates and more flexible interior layouts.
  • Energy Savings: Moving a heavier load with a single motor and counterweight can be more efficient than running two separate systems, especially when regenerative drives capture energy during braking.
  • Improved Handling Capacity: During peak hours (e.g., morning arrival or lunch rush), double-deck elevators move more people per minute than their single-deck counterparts.

Drawbacks and Considerations

  • Higher Initial Cost: The mechanical and control systems are more complex, raising upfront capital expenditure.
  • Door Synchronization Complexity: If one cab’s doors malfunction, both cabs must stop, potentially disrupting service across multiple floors.
  • Passenger Behavior: Occupants must be trained to use the correct cabin for their destination floor. Signage and destination dispatch systems can mitigate confusion, but it remains a challenge in buildings with frequent visitors.
  • Limited Flexibility: Fixed-spacing designs cannot accommodate floors with unusual ceiling heights without modifications.
  • Maintenance Challenges: Working on two stacked cabs requires specialized access and safety protocols.

Notable buildings that have deployed double-deck elevators include the One World Trade Center in New York (which uses a combination of double-deck and single-deck cars) and the Shanghai Tower in China, currently the world’s second-tallest building. The Burj Khalifa, while using mostly single-deck cars, incorporates double-deck designs in its observation deck shuttles to handle high visitor volumes.

Sky Lobbies: Vertical Transit Hubs

A sky lobby is an intermediate-level floor where passengers transfer between different elevator zones. Instead of a single elevator shaft running from ground to top, the building is divided into vertical segments—an express elevator carries passengers from the ground floor to a sky lobby, where they then board a local elevator that serves only a few floors within that zone. This zoning concept was pioneered in the 1970s in the original World Trade Center twin towers and has since become standard in supertall skyscrapers.

How Sky Lobbies Work

Sky lobbies serve as interchange stations. Typically, the building has two or three sky lobbies located at roughly one-third and two-thirds of the total height. Express elevators run non-stop to these lobbies, while local elevators connect the lobby to the floors within the zone. Some designs also include shuttle elevators that stop only at sky lobbies, bypassing all other floors.

For example, in the Petronas Towers in Kuala Lumpur, a sky bridge connects the two towers at levels 41 and 42, and a sky lobby at level 43 provides access to upper office floors. The Taipei 101 uses a double-deck elevator system in conjunction with sky lobbies to serve its observation deck efficiently.

Benefits of Sky Lobbies

  • Reduced Elevator Core Size: By grouping floors into zones, the total number of shafts needed is dramatically reduced. Express shafts are fewer and local shafts are shorter.
  • Faster Travel Times: Express elevators travel at high speeds (up to 10 m/s or more) without stopping, cutting travel time to upper floors by more than half compared to a single-shaft system.
  • Decongestion of Ground Lobby: Passengers are distributed to different sky lobbies, preventing the crush of people waiting at the main entrance.
  • Improved Emergency Evacuation: Sky lobbies can serve as refuge areas during fire or other emergencies, allowing occupants to move horizontally to another wing or wait for rescue.
  • Enhanced Security: Access to upper floors can be controlled at the sky lobby, requiring additional authorization.

Drawbacks of Sky Lobbies

  • Lost Rental Space: Each sky lobby occupies an entire floor that could otherwise be leasable space. Designers often offset this by placing the lobby at a mechanical floor or using it for amenities like conference centers or sky gardens.
  • Transfer Time: Passengers must wait for two elevators instead of one, adding 30–60 seconds per trip. In very tall buildings, this is a worthwhile trade-off.
  • Wayfinding Complexity: Visitors may be confused by the zoning system. Clear signage, mobile apps, and lobby attendants help, but it adds complexity.

Buildings with notable sky lobby systems include the Burj Khalifa (sky lobbies at levels 43, 76, and 123), the Shanghai World Financial Center, and the International Commerce Centre in Hong Kong. The concept is also used in many large mixed-use developments where a sky lobby connects residential and commercial zones.

Synergy: Combining Double-Deck Elevators and Sky Lobbies

When double-deck elevators and sky lobbies are combined, they create a powerful vertical transportation system that maximizes both capacity and speed. Double-deck express elevators can shuttle passengers to a sky lobby at double the per-trip capacity, while local double-deck elevators within each zone further increase throughput. This synergy is essential for the newest generation of supertall towers, which often exceed 100 floors and must move tens of thousands of people daily.

For instance, the Makkah Clock Royal Tower in Saudi Arabia uses double-deck shuttle elevators to move pilgrims quickly between the main entrance and upper hotel floors. In many new Asian skyscrapers, such as the Lotte World Tower in Seoul, a combination of double-deck cars and multiple sky lobbies handles both office and hotel traffic efficiently. The Council on Tall Buildings and Urban Habitat (CTBUH) details these emerging trends in its annual vertical transportation reports.

Next-Generation Elevator Technologies

Looking ahead, the elevator industry is pushing boundaries far beyond double-deck and sky lobby concepts. Several technologies are poised to redefine vertical transit in the coming decades.

AI-Driven Destination Dispatch

Traditional elevators use up and down buttons. Destination dispatch systems, now standard in many new installations, require passengers to key in their floor before boarding. An AI algorithm groups passengers with similar destinations, assigning them to a specific car. This reduces travel time and energy consumption. Advanced systems can learn traffic patterns and adapt in real time, even during special events or emergencies.

Ropeless Elevators (MULTI System)

One of the most revolutionary concepts is the ropeless elevator, developed by thyssenkrupp as the MULTI system. Instead of a single cable or belt, multiple cabs run independently in a closed loop—similar to a horizontal metro system turned vertical. Using linear motor technology and magnetic levitation, MULTI allows multiple cabs to travel in the same shaft, both up and down, and even turn sideways. This enables continuous circulation, higher capacity, and smaller cores. The first installation was completed in 2017 at the company's test tower in Rottweil, Germany, and a commercial deployment is planned for the East Side Tower in Berlin. For more details, see thyssenkrupp’s official MULTI page.

Maglev Elevators

Magnetic levitation (maglev) elevators use electromagnetic forces to suspend and propel the car without physical contact. This eliminates friction, enabling speeds of up to 20 m/s or more. Japan’s Hitachi and Mitsubishi Electric have been developing maglev prototypes, and a demonstration elevator in Japan’s 300-meter tall Abeno Harukas building runs at 12.5 m/s using a linear synchronous motor. Maglev systems also generate less noise and require less maintenance than traditional geared or gearless traction systems.

Green and Regenerative Technologies

Elevators are energy-intensive, but new designs are making them more sustainable. Regenerative drives convert the braking energy of descending cars into electricity, which can be fed back into the building’s grid. LED lighting, sleep-mode controls, and energy-efficient motors reduce overall consumption. Some buildings are even pairing elevator systems with on-site renewable energy sources, such as solar panels on the roof or wind turbines integrated into the building’s façade.

Impact on Architectural Design

The evolution of elevator technology has a direct impact on how skyscrapers are designed. Double-deck elevators allow for narrower cores, freeing more floor space for usable area. Sky lobbies create opportunities for sky gardens, atria, and public spaces at height, improving the occupant experience. Zoning with sky lobbies also permits mixed-use designs where different zones (e.g., offices, hotel, residences) have separate entrances and dedicated elevators.

Architects can now conceive buildings that are not just taller but also more efficient. For example, the Jeddah Tower in Saudi Arabia, currently under construction and aiming to exceed 1,000 meters, will rely on multiple sky lobbies and likely double-deck shuttles to service its various functions. The core becomes a vertical spine, with elevator shafts clustered around structural elements. This integration of structural and transportation engineering is a hallmark of modern supertall design.

The Elevator World magazine frequently reports on these architectural trends, highlighting how elevator technology influences building massing, floor plate efficiency, and even energy codes.

Challenges and Considerations

Despite the advantages, implementing double-deck elevators and sky lobbies is not without obstacles. Retrofitting an existing building with a double-deck system typically requires enlarging the shaft and reinforcing the structure, which is often cost-prohibitive. Sky lobbies may not be suitable for buildings with less than 40 floors because the transfer penalty outweighs the benefit.

Cost remains the overriding factor: a double-deck elevator can be 30–50% more expensive than a single-deck system of equivalent capacity. Additionally, maintenance requires specialized technicians trained in double-deck mechanics and controls. Passenger experience also demands careful design—confusing signage or long walks between transfer points can negate the time savings.

Safety regulations are evolving to keep pace. The American Society of Mechanical Engineers (ASME) A17.1/CSA B44 Safety Code for Elevators and Escalators now includes provisions for double-deck elevators, covering door interlocking, emergency stops, and evacuation procedures. Building owners must ensure compliance with local codes, which can vary widely across jurisdictions.

The Future of Urban Mobility

Elevator technology is not evolving in isolation. Smart building systems, Internet of Things sensors, and predictive maintenance algorithms are creating a seamless vertical transportation network. Passengers may soon use their smartphones to call an elevator, which automatically routes them to the optimal car and even adjusts the speed based on traffic. AI will balance load across multiple double-deck cars and sky lobbies in real time.

In the ultimate vision, elevators could become part of a connected urban mobility system, linking subway stations, parking garages, and sky bridges. The Hyperloop and vertical take-off and landing vehicles may one day converge with elevator systems, but for now, the focus remains on making existing technology smarter and more efficient.

As skyscrapers become taller, more mixed-use, and more sustainable, double-deck elevators and sky lobbies will undoubtedly play a central role. They allow architects to push the limits of height while maintaining practical passenger flow. Companies like Otis, Schindler, KONE, and Mitsubishi Electric continue to innovate, investing in research and development that promises faster, safer, and greener vertical travel.

For building owners and developers, investing in these advanced transportation systems is not optional—it is a necessity for staying competitive in the market for prime commercial and residential space. The future of elevator technology is double-deck, sky-lobby-equipped, and AI-optimized, and it is arriving faster than many realize.