You go down to the platform, open your map so you don't get lost, and... the signal bar goes blank. If you're traveling with an eSIM and wondering why your internet on the underground metro is spotty, the short answer is simple: underground coverage doesn't depend on your eSIM, but on whether that metro network has antennas installed in the tunnels. In this guide, I'll explain where it works, where it doesn't, and how to be prepared.
Does eSIM work underground?
Yes, an eSIM works just like a physical SIM: it connects to the local operator's antennas. The problem isn't the eSIM; it's that there's usually no signal underground. In stations and tunnels with repeater antennas, you'll have perfect 4G or 5G; in tunnels without coverage, neither your eSIM nor any mobile will have data until you reach the surface.
It's important to understand this before traveling because many people blame the eSIM when it's actually a "blind" tunnel. The same card that goes silent between two stations will give you full-speed data again when you reach the platform if that platform has a repeater. If you want to review how the technology works internally, you can find the complete explanation in what an eSIM is.
Why the signal cuts out in tunnels
Mobile waves travel through the air and weaken when passing through concrete, earth, and iron. A metro tunnel is practically a cage: without an antenna installed inside, the signal cannot enter. That's why many older networks only provide coverage in stations, not on the journey between them.
There are three typical scenarios you'll encounter as a traveler:
- Full coverage: antennas on platforms and in tunnels; continuous internet (modern networks in Asia and Northern Europe).
- Station only: you have data when stopped, but it cuts out when the train starts. This is the most common case.
- Zero coverage: old or very deep lines where nothing gets through until you exit.
The band matters: 5G is very fast but penetrates enclosed spaces worse than 4G, so sometimes you'll see 5G on the platform and the phone "drops" to 4G as soon as you enter the tunnel.
Traveler tip: If your map app allows you to download the city offline, do so before going down to the metro. You'll still see your approximate location and stops even if you lose data.
Metros with good coverage (and those that don't)
Not all metros in the world are the same. As a general guide for planning, here’s the overall picture based on eSIM traveler experiences:
| City / Network | Tunnel Coverage | Public WiFi |
|---|---|---|
| Seoul, Tokyo, Singapore | Complete (4G/5G throughout the journey) | Yes, free |
| London (Elizabeth line and extensions) | Partial, growing by lines | Yes, on platforms |
| Paris, Madrid, Barcelona | Good in station, irregular in tunnel | Limited |
| New York | Stations only | Yes, in stations |
| Old and deep metros | Scarce or none | Variable |
If you travel to Asia, it's likely you'll have uninterrupted data throughout your journey, something that's taken for granted there. In Europe, it depends heavily on the line and the year it was built. The practical recommendation: don't take underground connection for granted and have a backup plan.
Metro WiFi: when it's convenient
Many metro networks offer free WiFi in stations. It's useful for sending a quick message or checking the line, but it has drawbacks: it usually requires registration, it's slow during peak hours, and it disappears as soon as the train starts moving. Furthermore, open public transport WiFi networks are not the ideal place to do banking or enter passwords.
The advantage of an eSIM over public WiFi is that it uses the operator's encrypted mobile network, not an open hotspot shared by thousands of people. If you have data on the platform, you're usually safer relying on your eSIM than on the station's WiFi. And if you need to provide internet to another device while waiting, you can activate the shared hotspot from your eSIM.
Tips to avoid losing connection
Just because a tunnel doesn't have a signal doesn't mean you have to go blind. With a little foresight, you'll be covered:
- Download the offline map of the city and your route before going down.
- Take screenshots of the metro map and your destination stop.
- Write the message before losing signal: it will send automatically when you regain data upon exiting.
- Manually reactivate data if your phone takes time to reconnect after exiting the tunnel (toggle airplane mode on and off).
- Adjust your usage: review how much data each app uses so a small plan lasts you the entire trip.
If you're going to use public transport a lot, planning your data usage well prevents surprises. These tips for saving data abroad will help your eSIM last all your days without needing to top up mid-trip.
eSIM, coverage, and what to really expect
To summarize the important points: an eSIM gives you internet whenever there's a local operator network. In a city, you'll have stable 4G/5G on the street, in hotels, cafes, and most platforms; underground, between stations, you'll depend on whether that specific line has antennas. It's not a defect of your card; it's the physics of tunnels.
The good news is that outside the metro, the coverage of a travel eSIM is practically identical to that of a local SIM, because it relies on the same antennas. With 218 destinations available and activation in 1 minute, you'll be connected from the airport. And if your metro journey is interrupted, you know that as soon as you step out onto the street, you'll have all your data back at full speed. For extreme cases like boats or remote areas, also check the eSIM coverage on cruises, where the challenge is similar.
Frequently asked questions
Why do I lose internet on the metro with eSIM?
Because the tunnel between stations doesn't have a mobile antenna. It's not the eSIM's fault: no phone would have data there. When you exit the tunnel or reach a platform with a repeater, the connection automatically returns without you having to do anything.
Which metros in the world have full coverage?
Modern networks such as those in Seoul, Tokyo, Singapore, or Hong Kong offer 4G/5G throughout the journey, including tunnels. In Europe and New York, coverage is usually limited to stations, although it's expanding to more lines each year.
Is it better to use metro WiFi or eSIM?
If you have data with an eSIM, the eSIM is better: it uses the operator's encrypted network and is more secure than an open public WiFi. Metro WiFi is useful for quick tasks on the platform, but it's usually slow and cuts out when the train starts moving.
How do I get the map on the metro without a connection?
Download the area on your map app before going down. Google Maps and Maps.me allow you to save the city offline and still see your route and stops even if you lose the signal in the tunnel. Combine it with a screenshot of the metro map.
Does eSIM work on trains and road tunnels?
Yes, as long as there is coverage. On high-speed trains and long tunnels, there may be occasional cuts for the same reasons as in the metro, but on normal journeys through cities and on roads, the eSIM provides data with complete normality.
Conclusion
Your eSIM connects you to the best available network at all times; if there's no antenna underground, no miracle is possible, but as soon as you return to the surface, you'll regain full access. With a downloaded map and a couple of tricks, the metro stops being a problem. Travel with an eSIM that activates in 1 minute and works in 218 destinations and forget about searching for WiFi at every station.
