Why are subway stations platforms +15 F/+8 C hotter than ambient temperature in summer [closed]
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It was pleasant this morning in NYC 77F/25C: I did not break a sweat walking to the station. In contrast, the platforms of the #6 train at 42nd and 77th felt 15F/8C degrees hotter. I was not the only one sweating.
What causes the appreciable temperature increase in the station?
trains
edited Aug 2 at 3:56
dda
13.7k32548
asked Aug 1 at 14:20
gatorback
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closed as off-topic by Musonius Rufus, choster, Dirty-flow, David Richerby, gmauch Aug 1 at 15:44
- This question does not appear to be about traveling within the scope defined in the help center.
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show 2 more comments
up vote
2
down vote
favorite
It was pleasant this morning in NYC 77F/25C: I did not break a sweat walking to the station. In contrast, the platforms of the #6 train at 42nd and 77th felt 15F/8C degrees hotter. I was not the only one sweating.
What causes the appreciable temperature increase in the station?
trains
edited Aug 2 at 3:56
dda
13.7k32548
asked Aug 1 at 14:20
gatorback
1,232525
closed as off-topic by Musonius Rufus, choster, Dirty-flow, David Richerby, gmauch Aug 1 at 15:44
- This question does not appear to be about traveling within the scope defined in the help center.
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
6
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
1
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
4
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
1
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37
 |Â
show 2 more comments
up vote
2
down vote
favorite
up vote
2
down vote
favorite
It was pleasant this morning in NYC 77F/25C: I did not break a sweat walking to the station. In contrast, the platforms of the #6 train at 42nd and 77th felt 15F/8C degrees hotter. I was not the only one sweating.
What causes the appreciable temperature increase in the station?
trains
edited Aug 2 at 3:56
dda
13.7k32548
asked Aug 1 at 14:20
gatorback
1,232525
It was pleasant this morning in NYC 77F/25C: I did not break a sweat walking to the station. In contrast, the platforms of the #6 train at 42nd and 77th felt 15F/8C degrees hotter. I was not the only one sweating.
What causes the appreciable temperature increase in the station?
trains
edited Aug 2 at 3:56
dda
13.7k32548
asked Aug 1 at 14:20
gatorback
1,232525
edited Aug 2 at 3:56
dda
13.7k32548
edited Aug 2 at 3:56
dda
13.7k32548
edited Aug 2 at 3:56
dda
13.7k32548
13.7k32548
asked Aug 1 at 14:20
gatorback
1,232525
asked Aug 1 at 14:20
gatorback
1,232525
asked Aug 1 at 14:20
gatorback
1,232525
1,232525
closed as off-topic by Musonius Rufus, choster, Dirty-flow, David Richerby, gmauch Aug 1 at 15:44
- This question does not appear to be about traveling within the scope defined in the help center.
closed as off-topic by Musonius Rufus, choster, Dirty-flow, David Richerby, gmauch Aug 1 at 15:44
- This question does not appear to be about traveling within the scope defined in the help center.
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
6
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
1
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
4
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
1
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37
 |Â
show 2 more comments
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
6
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
1
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
4
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
1
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
6
6
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
1
1
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
4
4
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
1
1
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37
 |Â
show 2 more comments
1 Answer
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An S7 underground train, as used on the Circle Line, weighs 213.7 tonnes empty, and carries up to 1045 passengers at speeds of up to 100km/h. A train carrying 500 passengers of average mass 60kg decelerating from 80km/h (22m/s) to stationary must get rid of 60MJ of energy via its brakes, which will be dissipated as heat into the environment.
If the platform is 120m long, and is of semi-circular cross-section with radius 5m, that energy is dumped into at most 5,000m^3 of air. My faithful old Science Data Book says that average air has a density of 1.293 kg/m^3 and a specific heat capacity of 993 J/kgK, so each train's energy causes a temperature rise of around 9K (9C, ~16F) in that air.
There are lots of confounding variables; you asked about New York, for a start. S7 stock has regenerative brakes that are able to shunt about 20% of that energy back into the network, trains on short inner-city runs probably don't get up to 80km/h between stations, the passage of the trains pulls air in and out of the tubes, most platforms have ventilation systems, the brakes are unlikely to cool to ambient temperature in the short time it takes to let passengers on and off, and so on. But on the face of it, trains do provide a significant heat source to the platform environment.
Edit: because comments threads can disappear around these parts, particularly on closed questions, I wish to link to an excellent article on the subject, drawn to my attention by Patricia Shanahan, to whom much thanks. It provided a much more detailed analysis of the contributors to heat in the system, and helpfully confirms that braking is the dominant contributor. It also discusses in much more detail how heat is removed from the system, and concludes that the battle can only be won by decreasing dissipated brake heat.
answered Aug 1 at 14:41
MadHatter
6,57312544
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
 |Â
show 3 more comments
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
13
down vote
An S7 underground train, as used on the Circle Line, weighs 213.7 tonnes empty, and carries up to 1045 passengers at speeds of up to 100km/h. A train carrying 500 passengers of average mass 60kg decelerating from 80km/h (22m/s) to stationary must get rid of 60MJ of energy via its brakes, which will be dissipated as heat into the environment.
If the platform is 120m long, and is of semi-circular cross-section with radius 5m, that energy is dumped into at most 5,000m^3 of air. My faithful old Science Data Book says that average air has a density of 1.293 kg/m^3 and a specific heat capacity of 993 J/kgK, so each train's energy causes a temperature rise of around 9K (9C, ~16F) in that air.
There are lots of confounding variables; you asked about New York, for a start. S7 stock has regenerative brakes that are able to shunt about 20% of that energy back into the network, trains on short inner-city runs probably don't get up to 80km/h between stations, the passage of the trains pulls air in and out of the tubes, most platforms have ventilation systems, the brakes are unlikely to cool to ambient temperature in the short time it takes to let passengers on and off, and so on. But on the face of it, trains do provide a significant heat source to the platform environment.
Edit: because comments threads can disappear around these parts, particularly on closed questions, I wish to link to an excellent article on the subject, drawn to my attention by Patricia Shanahan, to whom much thanks. It provided a much more detailed analysis of the contributors to heat in the system, and helpfully confirms that braking is the dominant contributor. It also discusses in much more detail how heat is removed from the system, and concludes that the battle can only be won by decreasing dissipated brake heat.
answered Aug 1 at 14:41
MadHatter
6,57312544
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
 |Â
show 3 more comments
up vote
13
down vote
An S7 underground train, as used on the Circle Line, weighs 213.7 tonnes empty, and carries up to 1045 passengers at speeds of up to 100km/h. A train carrying 500 passengers of average mass 60kg decelerating from 80km/h (22m/s) to stationary must get rid of 60MJ of energy via its brakes, which will be dissipated as heat into the environment.
If the platform is 120m long, and is of semi-circular cross-section with radius 5m, that energy is dumped into at most 5,000m^3 of air. My faithful old Science Data Book says that average air has a density of 1.293 kg/m^3 and a specific heat capacity of 993 J/kgK, so each train's energy causes a temperature rise of around 9K (9C, ~16F) in that air.
There are lots of confounding variables; you asked about New York, for a start. S7 stock has regenerative brakes that are able to shunt about 20% of that energy back into the network, trains on short inner-city runs probably don't get up to 80km/h between stations, the passage of the trains pulls air in and out of the tubes, most platforms have ventilation systems, the brakes are unlikely to cool to ambient temperature in the short time it takes to let passengers on and off, and so on. But on the face of it, trains do provide a significant heat source to the platform environment.
Edit: because comments threads can disappear around these parts, particularly on closed questions, I wish to link to an excellent article on the subject, drawn to my attention by Patricia Shanahan, to whom much thanks. It provided a much more detailed analysis of the contributors to heat in the system, and helpfully confirms that braking is the dominant contributor. It also discusses in much more detail how heat is removed from the system, and concludes that the battle can only be won by decreasing dissipated brake heat.
answered Aug 1 at 14:41
MadHatter
6,57312544
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
 |Â
show 3 more comments
up vote
13
down vote
up vote
13
down vote
An S7 underground train, as used on the Circle Line, weighs 213.7 tonnes empty, and carries up to 1045 passengers at speeds of up to 100km/h. A train carrying 500 passengers of average mass 60kg decelerating from 80km/h (22m/s) to stationary must get rid of 60MJ of energy via its brakes, which will be dissipated as heat into the environment.
If the platform is 120m long, and is of semi-circular cross-section with radius 5m, that energy is dumped into at most 5,000m^3 of air. My faithful old Science Data Book says that average air has a density of 1.293 kg/m^3 and a specific heat capacity of 993 J/kgK, so each train's energy causes a temperature rise of around 9K (9C, ~16F) in that air.
There are lots of confounding variables; you asked about New York, for a start. S7 stock has regenerative brakes that are able to shunt about 20% of that energy back into the network, trains on short inner-city runs probably don't get up to 80km/h between stations, the passage of the trains pulls air in and out of the tubes, most platforms have ventilation systems, the brakes are unlikely to cool to ambient temperature in the short time it takes to let passengers on and off, and so on. But on the face of it, trains do provide a significant heat source to the platform environment.
Edit: because comments threads can disappear around these parts, particularly on closed questions, I wish to link to an excellent article on the subject, drawn to my attention by Patricia Shanahan, to whom much thanks. It provided a much more detailed analysis of the contributors to heat in the system, and helpfully confirms that braking is the dominant contributor. It also discusses in much more detail how heat is removed from the system, and concludes that the battle can only be won by decreasing dissipated brake heat.
answered Aug 1 at 14:41
MadHatter
6,57312544
An S7 underground train, as used on the Circle Line, weighs 213.7 tonnes empty, and carries up to 1045 passengers at speeds of up to 100km/h. A train carrying 500 passengers of average mass 60kg decelerating from 80km/h (22m/s) to stationary must get rid of 60MJ of energy via its brakes, which will be dissipated as heat into the environment.
If the platform is 120m long, and is of semi-circular cross-section with radius 5m, that energy is dumped into at most 5,000m^3 of air. My faithful old Science Data Book says that average air has a density of 1.293 kg/m^3 and a specific heat capacity of 993 J/kgK, so each train's energy causes a temperature rise of around 9K (9C, ~16F) in that air.
There are lots of confounding variables; you asked about New York, for a start. S7 stock has regenerative brakes that are able to shunt about 20% of that energy back into the network, trains on short inner-city runs probably don't get up to 80km/h between stations, the passage of the trains pulls air in and out of the tubes, most platforms have ventilation systems, the brakes are unlikely to cool to ambient temperature in the short time it takes to let passengers on and off, and so on. But on the face of it, trains do provide a significant heat source to the platform environment.
Edit: because comments threads can disappear around these parts, particularly on closed questions, I wish to link to an excellent article on the subject, drawn to my attention by Patricia Shanahan, to whom much thanks. It provided a much more detailed analysis of the contributors to heat in the system, and helpfully confirms that braking is the dominant contributor. It also discusses in much more detail how heat is removed from the system, and concludes that the battle can only be won by decreasing dissipated brake heat.
answered Aug 1 at 14:41
MadHatter
6,57312544
edited Aug 2 at 10:52
answered Aug 1 at 14:41
MadHatter
6,57312544
answered Aug 1 at 14:41
MadHatter
6,57312544
answered Aug 1 at 14:41
MadHatter
6,57312544
6,57312544
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
 |Â
show 3 more comments
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
And also, all the bodies that are in the station and the train give quite a bit of heat themseves, too.
– SJuan76
Aug 1 at 22:04
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
@SJuan76 my wife raised that point, so I ran some numbers for that, and got less than 10% of the braking heat dissipation. But your figures may differ - do feel free to show them!
– MadHatter
Aug 1 at 22:51
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
Let’s add the fact that NYC subway rolling stock has air conditioning. Cooler inside means hotter outside.
– jcaron
Aug 1 at 22:56
1
1
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
The London Underground deep tunnels are a special problem. They run through clay that does not conduct heat well, and some have been running for over 100 years. See Cooling the tube – Engineering heat out of the Underground
– Patricia Shanahan
Aug 2 at 6:17
2
2
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
@PatriciaShanahan this may not be the place for this discussion, but there may be a misunderstanding. As long as the clay was cool, the cold sink it provided was non-negligible - it provided a significant cooling effect in the early days (see, eg, The deep tube tunnels section of your marvellous article) and so provided a significant confounding variable to the back-of-an-envelope heat calculation I did above. As the clay has warmed up, it is less useful as a cold sink because it is no longer cold, and so its confounding effect has become negligible.
– MadHatter
Aug 2 at 10:45
 |Â
show 3 more comments
Clash Royale CLAN TAG
This seems off-topic, but it's probably due to the heat generated by the trains themselves and the fact that the further down you go the temperature is more and more constant throughout the year. The heat from the sun just doesn't penetrate deep enough.
– Guido
Aug 1 at 14:28
6
I'm voting to close this question as off-topic because it's focus is not travel.
– Musonius Rufus
Aug 1 at 14:33
1
A why question like this is probably better-suited to Physics. It's hot because you're underground and the air pressure is higher, and because the trains are throwing off a tremendous amount of energy when they brake.
– choster
Aug 1 at 14:59
4
@choster Higher air pressure doesn't cause increased temperature. Sure, if you take air and compress it, it will heat up, but that's in a dynamic situation. In the static situation (where the air has already been compressed and you're not compressing it any more), it will equalize its temperature with its surroundings, just like anything else.
– David Richerby
Aug 1 at 15:35
1
@MadHatter The mass, length and speed of Circle Line trains are not travel-related in the sense of this site: a traveller doesn't need to know any of those things.
– David Richerby
Aug 1 at 15:37