Under the trial scheme, instruments under 145cm in length would be allowed to travel with a pre-registered permit all day except during the peak hour of 8.15am to 9.15am. Registration, online or at designated MTR stations, starts on Monday.

On the surface, some, such as cellists with their 135cm cello, may feel a relief. But those with instruments above the new extended limit, such as a 183cm double bass and a 163cm , are left out in the cold. The MTR has made it clear that oversized instruments would not be permitted aboard and frontline staff would strictly enforce the rules, unlike before.

The sudden crackdown on large musical instruments starting from mid-September puzzled even the MTR's chairman-designate Frederick Ma Si-hang. It remained a mystery until Secretary for Transport and Housing Professor Anthony Cheung Bing-leung last month that it was the government that asked for a strict enforcement of the rules, targeting primarily parallel-goods traders.

In the crackdown, the affected musicians became "collateral damage". More ominously, the unfriendly fire hit only young local students, including three cellists and one player.

The decision to ban the double bass reflects a blatant ignorance of the arts, on which the government spent HK$3.5 billion last financial year in promotion efforts. The double bass is the biggest member of the violin family of four. Unlike the cello, a double bass cannot fit into a taxi or even some minivans. Taking the subway is the only feasible way for these instruments to travel. The same applies to a full-size 163cm . But how often do musicians carry these instruments around? Most don't do so unless absolutely necessary.

The city's three professional orchestras take care of their large instruments on private coaches. These instruments are vulnerable and can't risk even a light contact on train doors or roof as the neck can snap easily. Even students without corporate support rarely carry large instruments on train. Why bother to make a big issue out of a small number of users after three decades of safety record?

Like it does for wheelchair passengers, the MTR should also cater to the special needs of musicians with large instruments. Safety concerns are not a valid reason to deny them. In the case of an emergency evacuation, an instrument strapped to the body is far less dangerous than a baby trolley or a two-wheel cart with a packed bag.

The case of bicycles on the MTR deserves a mention. If it, after disengaging the front wheel, could make it to the train without registration or restrictions, then why should a cello, stored inside a rounded case, be scrutinised?

READ MORE: Hong Kong's MTR hits a major wrong note in cello case

That musical instruments would end up being subject to such rules is a sad case of an increasingly paranoid city that resorts to "thou shalt not" regulations rather than a civic spirit for solutions. By using specific rules and regulations rather than trust and discretion, the MTR is opening a can of worms for itself: there will be endless centimetres to measure, from training swords to rods.

An alternative to all this is to do nothing, then sit back and listen to the music played by happy musicians.