The complex design of the new $4 billion Transbay Transit Center just got a little more intricate. On July 11, the Transbay Joint Powers Authority (TJPA) announced it will incorporate a groundbreaking geometric pattern known as the Penrose Rhombus Tiling into exterior walls on the project.

Developed by eminent British mathematical physicist Dr. Roger Penrose, the elegant design pattern is remarkably simple but unique because it can be extended infinitely without repeating itself. The Penrose system is ideal for the perforations in the metal panels that will form the curved exterior of the Transit Center.

Designed by Pelli Clarke Pelli Architects (PCPA), the Transbay Transit Center is scheduled to complete in fall 2017. Official are calling it a visionary transportation and housing project that will transform downtown San Francisco and the San Francisco Bay Area’s regional transportation system by creating a “Grand Central Station of the West” in the heart of a new transit-friendly neighborhood.

The project will replace the current Transbay Terminal at First and Mission streets in San Francisco with a modern regional transit hub connecting eight Bay Area counties and California through 11 transit systems.

Work consists of three interconnected elements: replacing the former Transbay Terminal at First and Mission streets; extending Caltrain and California High Speed Rail underground from Caltrain’s current terminus at 4th and King streets into the new downtown Transit Center; and creating a new neighborhood with homes, offices, parks and shops surrounding the new Transit Center.

Webcor/Obayashi, Joint Venture is the CM/GC for Phase I of the project. This portion will include the construction of a new five-story Transit Center Building with one above-grade bus level, ground-floor, concourse, and two below-grade rail levels serving Caltrain and the future California High Speed Rail. It will also include a 5.4 acre public rooftop park.

The Penrose Rhombus Tiling, discovered in 1974, was heralded by mathematicians and physicists and helped give birth to a new scientific field called quasicrystals, which spawned discoveries in material science and biology.

The discovery initially yielded designs that were only known to exist in synthetic materials. Patterns similar to Penrose’s design, however, have recently been found in natural materials such as those in meteorites.

When used at the scale of the new Transit Center, the pattern creates a delicate, lace-like screen that is an ideal contrast to the monumental structure of the Transit Center, say officials. PCPA, which is working in tandem with Dr. Penrose, says the Penrose Pattern on the exterior of the building will symbolize the interconnections among mathematics, science and art which are so deeply ingrained in the rich, technologically advanced culture of the Bay Area.

The non-repeating pattern of the tiling is well suited to the complex curved form of the Transit Center exterior. To achieve the undulating sensation of the Transit Center exterior, PCPA has designed multiple metal panels of varying sizes and trapezoidal shapes that require seamless visual transitions from panel to panel—a visual effect that can be achieved only with a non-periodic pattern .

The pearlescent white metal skin of the Transit Center will be perforated with the Penrose pattern, letting 35 % of the wall surface remain open to light and air. The passenger experience from the inside will be one of openness and diffused light.

Dr. Penrose also developed the famous “Penrose Triangle” which artist M.C. Escher used in many of his pieces, including "The Waterfall" in 1961.