On a United Airlines flight from Newark to Denver in August, a small piece of plastic caused an unexpected diversion to another airport – and headlines around the world. It started when one passenger had used a “Knee Defender” – a $21.95 piece of plastic that attaches to the tray table and blocks the seat in front in an upright position. A furious row ensued, with name-calling and drinks being thrown – and the plane had to make an emergency stop in Chicago, with police escorting both passengers off the flight.

The use of the Knee Defender is an extreme example of some of the tricks we use to try and make our commute – by bus, train or plane – that little bit more comfortable. The fight for space on public transport can turn the meekest among us into a rebel. But while we might be aware of the tricks we pull to afford ourselves that extra bit of space, we’re not necessarily aware of those being played on us by transport operators – the “nudge”.

Persuading people to do the right thing when they’re travelling is a nuanced business. The nudge is the unspoken ushering towards a way of acting that makes life easier for everyone, be it on a cramped Tube train or a commuter flight. So how do they trick us into behaving the way they want – ideally without us even noticing they are doing it?

Armrest update

Let’s take the popular sport of elbow fights over armrests in aeroplanes. Sometimes it can be a simple design nudge that keeps the peace. Paperclip Design, a Hong Kong-based company, has developed a prototype of an armrest that has two levels; while one passenger’s elbow rests on top, the other’s fits at the lower level of the armrest, says inventor James Lee, the company’s director.

It’s still a concept, but small-scale trials suggest that it makes for happier passengers, he says. “It can reduce significant frustration regarding the space for elbows,” says Lee. Now the firm is “in discussions with some interested parties”.