These 'pinch point' barriers at London's Heathrow Airport prevent the baggage trolleys from the Bus Station being taken down the escalators which lead to Terminals 1, 2 and 3. Mistake-proofing (for safety reasons: a trolley down the escalator would be dangerous) but also unnecessary if the airport had been designed differently from the start. Is forcing users to load baggage on and off multiple trolleys whenever their path descends or ascends really desirable? A lift (elevator) may be available, but how many people - and their trolleys - can fit in it at once?
An inclined travelator (as used elsewhere at Heathrow) would be a better solution.