Tube's hottest lines unveiled
London - A map of the warmest spots of London's subway system was released on Monday, revealing what commuters already know: It can get hot on the Tube.
The world's oldest subway system is not air conditioned, and as London temperatures reach 30ºC this summer, commuters crammed into cars often gasp for air each time the doors open to let even more passengers on board.
The new heat map, published by The Times of London but not yet officially made public, shows measures for the temperatures in each of the 11 Tube line's tunnels can get as hot as 30ºC.
That is also the maximum temperature for transporting cattle to slaughter houses, according to the UK's Department for Environment, Food and Rural Affairs.
Even the cooler lines, though, rarely drop below 26ºC during the Tube's busiest times. And while the map measures tunnel temperatures, it can often seem hotter in the train cars. Transport for London officials say they don't actually check the temperatures in the cars - so it is really anyone's guess.
The map, set against a black background, lays out each of the Tube tunnel's maximum temperatures by replacing the regular map shades with a colour-coded temperature guide going from soft green to yellow-orange and then to red.
The Tube's narrow tunnels, built long-before air conditioning was invented, are only large enough to fit trains.
Transport for London said the map has long been used by engineers responsible for keeping the London Underground bearable for commuters - the so-called Cooling the Tube team.
Over the next five years the team plans to double the capacity of fans at all of the main ventilation shafts on the Victoria Line in an effort to cool it down.
London Mayor Boris Johnson has said the first air-conditioned trains should be running next year on the network's Metropolitan Line.
By 2015, air conditioning is expected on four lines, or less than half of the system.