Earlier this week, the Tashkent Metro announced a significant reduction in train speeds and even the possible suspension of service due to high temperatures. The announcement appears to refer to the elevated sections of the metro system, although this is not explicitly stated. These elevated lines make up a substantial part of the network. It is worth noting that hot weather in Tashkent lasts at least three months each year and often much longer.
“Due to the start of the summer season, air temperatures in the city of Tashkent are rising sharply, and as a result the temperature of metro rails and copper components may become very high, reaching up to +70 degrees,” the statement said.
The Tashkent Metro further explained that under its operating regulations, train speeds are reduced when rail temperatures exceed +55°C. When rail temperatures reach +60°C, train speeds are limited to 40 km/h. At +65°C, train speeds must not exceed 25 km/h. When rail temperatures reach +70°C or higher, train movement is restricted.
“To ensure the safety of train operations and passengers during periods of high temperatures, temporary speed restrictions will be introduced on the Yer usti halqa yo‘li metro line and on the Sergeli sections,” the metro press service said.
If data on the difference between air and rail temperatures in central and southern regions of Russia (24–26°C) are applied to Tashkent, restrictions on elevated metro operations could begin at air temperatures of around 29°C, speeds could be reduced to 40 km/h at 34°C, limited to 25 km/h at 39°C, and a complete suspension of service could occur at approximately 44°C. I found these figures during a brief internet search.
“Changes in rail temperature occur under conditions of complex heat exchange. During summer, rails exposed to sunlight absorb thermal energy, while part of that energy is lost through radiation and heat transfer to the surrounding environment. As the rail heats up (when more heat is absorbed than dissipated), temperatures at different points along the rail continue to rise over time,” according to material published by the Ural Railway.
Rail temperature depends on many factors, including air temperature, rail type and surface condition, rail orientation relative to the cardinal directions, track alignment and profile, the cross-sectional profile of the track bed, the intensity of solar radiation and atmospheric transparency, wind speed and direction, the quality and reflectivity of ballast, and a number of other factors.
The difference between rail and air temperatures in summer reaches 24–26°C in central and southern regions of Russia. I could not find comparable data for Uzbekistan and assume the difference may be even greater. For the most optimistic scenario, the relationship can be expressed as:
tr = ta + 26°C
where:
tr — rail temperature;
ta — air temperature.
Accordingly, the formula for calculating the air temperature corresponding to a given rail temperature is:
ta = tr − 26°C
As early as May, average temperatures in Tashkent approach 30°C. In June, July and August, temperatures can reach 43°C or higher.
This year, daytime temperatures in Tashkent were 29°C and above starting from 20 May, and reached as high as 34°C during May.
Metro specialists may, of course, use different formulas. If they share them, I would be glad to publish them. I would also like to know whether the designers of Tashkent’s new elevated metro lines took into account prolonged summer heat and projected climate warming during the design process. If so, how exactly?
The Tashkent Metro currently consists of five lines and 48 stations (31 underground, 14 elevated and 3 at ground level), with a total length of 67.2 kilometres. These figures were obtained through calculations and open sources because the information on the Tashkent Metro website was outdated as of 4 June 2023.
On 25 April, the press service of the Ministry of Transport reported that “passenger services began at five stations completed as part of Phase II of the elevated metro line ‘Qo‘yliq – Quruvchilar’, where the total length of the five stations is 7.74 kilometres.”
“As a result, the number of stations in the Tashkent Metro has reached 48,” the ministry said.
Still, I was not surprised. I have previously written about the problem of incompetence in various sectors across Uzbekistan.
What do you think about how the Tashkent Metro operates in hot weather? Share your thoughts in the comments.