A district line train to Upminster arriving at Tower Hill Station. Image courtesy of Wikipedia
Arriving at an Underground station and seeing the words “severe delays” (usually as a result of a signal failure somewhere on the circle line) most commuters can’t help but feel let down by the world’s first underground railway.
The tube’s apparent inefficiency makes it sometimes hard to remember and appreciate that it relies on a large amount of science – a discipline usually regarded as efficient and logical.
So in an attempt to remind all you frustrated commuters out there that the tube is perhaps sometimes not as bad as you may think, here are two detailed science facts about the London Underground:
Engineering Excellence
No-one can argue that the London Underground tunnels are a remarkable engineering feat. With several of the current tube lines as much as 20 metres underground, eg. the Piccadilly, Central and Bakerloo Lines, the engineering dangers were also very apparant. Thankfully the necessary equipment had recently been developed when construction on the tube tunnels began.
In 1818, Sir Marc Isambard Brunel developed the original tunnelling shield. Effectively a support structure for maintaining the tunnel while it was being excavated, the shield allowed engineers and miners to work without the risk of the tunnel collapsing. It was used when the soil was unstable and helped maintain the structure whilst the tunnel was being lined with a support structure of concrete, cast iron or steel.
This design was then enhanced by Peter W. Barlow for his construction of the Tower Subway under the River Thames in 1870, which enabled miners to dig behind a watertight screen without damaging any properties above ground. Further developments occurred when Barlow joined with James Henry Greathead, enabling them to use their tunnelling experience to construct of the City & South London Railway (now part of the Northern Line) in 1884. This developement of the tunnelling shield has since enabled approximately 250 miles of track to be laid under London and its surrounding areas, serving 270 stations, with a daily weekday ridership of 3.4million passengers.
With the first London underground trains running on steam (the first electric trains were not used until 1890), other considerations were important in the construction of the tunnels. Ventilation shafts were built at various points along the routes to allow the engines to expel the steam and bring fresh air into the tunnels. One such vent is at Leinster Gardens where a concrete façade was constructed to resemble a genuine house frontage – in keeping with the visual aesthetics of the well-to-do street.
Can you spot which of these houses is a façade? Image courtesy of Wikipedia
Some further great photos of the structure can be seen here.
Air Pollution
An “urban myth”: https://en.wikipedia.org/wiki/London_Underground_air_pollution exists that suggests that 20minutes on the Tube is equivalent to smoking one cigarette and has even been previously quoted by the BBC and the London Evening Standard.
The myth originated from work done by Dr Ben Croxford, a researcher at University College London who at the request of a journalist carried out an estimate of the weight of particulate matter inhaled when smoking a cigarette. Croxford subsequently calculated that a person would have to spend 20minutes in the most polluted part of the London Underground to breathe in the same amount of matter.
However, the calculation only made a comparison of the weight of matter breathed in and Croxford’s research never intended to suggest that breathing in Underground dust was as harmful as smoking cigarettes. The subsequent interpretations of this data by the media is a classic example of how lying can be easily achieved with statistics and how scientists must be careful that their data does not mean the lay-reader draws an incorrect conclusion.
Dust in the tube tunnels is primarily iron (from the wheel-rail interface), quartz silica (from the train’s brakes), passengers’ clothing fibres and cells from human skin and hair.
These particulates are much less harmful than those found in traffic exhaust which have been found to aggravate asthma. . With concerns about asthma growing worldwide, particularly following the campaigning on Asthma Day 2009 last week, it’s reassuring to know that although the air you’re breathing in when squashed into a packed-tube might smell of body-odour, it’s unlikely to cause you too much harm.