What is the primary function of the Electronic Controlled Air Suspension (ECAS) 'kneeling' (Absenkung) feature on low-floor urban and intercity buses?

1. To increase ground clearance when driving over railway crossings and speed bumps
2. To lower the entrance side of the bus body by several centimeters to facilitate boarding for elderly passengers and PRMs
3. To deflate the front axle bellows completely during high-speed motorway cruising to reduce drag
4. To tilt the bus body away from the curb to prevent luggage scratching the exterior panels