Double-decker buses are engineered with an exceptionally low center of gravity, which prevents them from toppling even during sharp turns or steep tilts. The heavy components of the vehicle, such as the engine, transmission, fuel tanks, and the massive steel chassis, are all located beneath the floor of the lower deck. In contrast, the upper deck and the roof are constructed from lightweight materials like aluminum and glass. In the UK, these buses must pass a "tilt test" where they are inclined to an angle of 28 degrees without tipping over. Even when the top deck is fully loaded with passengers and the bottom is empty, the weight of the chassis remains the dominant force. As long as the cumulative center of gravity stays within the "footprint" of the wheels, the bus remains stable. Modern buses also utilize advanced anti-roll bars and electronic stability control systems to further mitigate swaying and ensure passenger safety in 2026.