Lifts are becoming more sustainable, as the percentage of the world’s population living in cities grows.

Each day, more than seven billion elevator journeys are taken in tall buildings all over the globe. Considering that half the world’s population live in cities—a number expected to jump to 70 percent by the year 2050—efficient vertical transportation has become a pressing challenge. To keep pace with an influx of urban dwellers and rising sea levels, developers will not only need to build higher, they will also need to devise greener vertical transport: that is, safe and sustainable ways to move residents from the ground up into the sky.

Newer elevators already incorporate green features such as LED lights, water soluble paint and recycled construction materials, but many companies have begun to explore a wide and somewhat outlandish array of alternatives to the traditional rope-and-pulley systems of a hundred years ago. From diagonal travel (Las Vegas’ Luxor hotel has an elevator that runs along its pyramid-shaped building at a 39-degree incline) to destination dispatch (grouping passengers bound for the same destinations into the same elevators) to something called magnetic motors (using a magnetic field to propel an elevator cab between floors), the world of vertical transport is one of high hopes and higher stakes.

We generally don’t give much thought to elevators, except during the brief moments we’re inside them. They may make us feel claustrophobic, awkward or impatient, but these vertical conveyances are in fact a marvel of engineering: not only do elevators shuttle passengers and freight up and down hundreds of stories—to hotel rooms and apartments, lobbies and basements—they also carry tons of steel cable each trip they make. The shafts in which they operate are essential to the structural integrity of a building, and their design can mean the critical difference between sustainable use of space and return on investment.

Unfortunately, many elevators in the United States rely on aging technology, clunky cabs and harmful lubricants, at significant environmental and financial cost. Consider that an elevator inside a typical skyscraper might weigh 80,000 pounds; hoisting all that mass requires a tremendous amount of energy. The taller the building, the more elevator shafts needed, each with their own motor; extra tall buildings often require a second sky lobby halfway between the ground floor and the roof. In fact, elevators typically account for between 2 percent and 10 percent of a building’s energy use. That includes materials—interior paints, carpet, control panels, lighting, ventilation systems—and the mechanical technology used to operate the cab itself.