“TAKE THE TWOPENNY tube and avoid all anxiety,” reads a vintage advertisement for the Central London Railway (CLR), an underground railway that operated in Britain’s capital during the early 1900s. The poster, dated 1905, would seem curious to Londoners today. The city’s subway system, a 400km stretch of tracks known as “the Tube”, has much to induce anxiety. Anti-social behaviour and overcrowding are the biggest irritations, according to a recent survey. Next is too much noise.

Indeed, noise levels on the Tube may be dangerously high. Eave, a London-based firm that designs hearing-protection gear, recently collected data on noise across the entire network. Data for the loudest tube lines—Victoria, Bakerloo, Jubilee and Northern—were shared with The Economist. They show that noise inside Underground carriages often reach 85 decibels (dB). This is the same level that, if sustained for eight hours a day, obliges British employers to provide workers with hearing protection. On the Victoria Line, the city’s most-used route, there is a five-minute stretch where noise levels average 90dB, about as loud as a lawn mower. The loudest journey through central London reaches a peak of 109dB, equivalent to a helicopter taking off.

Whether this is harming riders is unclear. Studies on the impact of the Underground on public health are hard to come by. The Tube’s most ear-splitting noise levels tend to last for only short periods, such as when the wheels of the carriage grind against the rails during turns. There is little doubt, however, that sustained traffic noise can damage human health. According to The World Health Organisation, railway traffic that averages at least 56 dB can cause “adverse health effects” for those living or working nearby, ranging from sleep disturbance to tinnitus, a constant ringing or buzzing in the ears. Other noise-related health woes are less obvious. A recent study commissioned by Transport & Environment, a pressure group, reckons that 245,000 Europeans suffer from heart disease that can be traced to noise pollution—noise-induced stress perhaps being the cause.

Transport for London (TfL), the tube’s operator, has insisted that noise levels on the tube are safe. But it may be waking up to the potential risks. In June, after drivers threatened to strike over excessive noise, TfL agreed to give them ear defenders.