Breaking: Athens Line 4 Tunneling Under Historic heart Progresses as Surface Traffic Flows
A newly released video offers a rare, close-up view of the subterranean work reshaping Athens’ transport future. The footage shows the city being literally excavated from below while daily life on the surface continues.
line 4 is advancing to connect high-demand districts such as Alsos Veikou, Exarchia, Kolonaki, Goudi and Zografou, using modern tunnel boring machines. In some stretches, operations run at depths beyond 30 meters, a method designed to minimize surface disruption but carrying elevated urban risk in a densely built area.
Inside the tunnels, the TBMs plow forward with millimeter precision, while segments are installed to form rings that stabilize the underground walls. This approach,widely employed in major European capitals,is viewed as essential for constructing subways beneath historic cores because it reduces ground movement and surface impact.
Industry analysts say Athens is adopting some of the most advanced underground construction practices today, with real-time monitoring of vibrations, ground movements and worker safety. Line 4 is seen as a pivotal solution to ease road congestion, expected to serve tens of thousands of daily passengers who currently rely on cars or buses.
The released footage also underscores the human dimension of the project, featuring technicians and engineers working with unusual precision in an surroundings that feels more like an underground operations hub than a typical construction site. When finished, Line 4 is anticipated to transform Athens’ travel patterns by boosting public transit use and shortening journeys in previously hard-to-reach areas.
As the project advances, the images serve not only as a technical chronicle but also as a reminder that modern cities evolve both above and below ground, with infrastructure that will shape life for decades to come.
Key Facts at a Glance
| Aspect | Detail |
|---|---|
| project | Athens Line 4 underground railway |
| Depth | Up to 30+ meters in some sections |
| connected districts | Alsos Veikou, exarchia, Kolonaki, Goudi, Zografou |
| Construction method | Tunnel Boring Machines with ring segments |
| Purpose | Relieve road congestion; serve tens of thousands daily |
| Monitoring | Real-time controls for vibrations, ground movement and worker safety |
Experts emphasize that such projects aim to protect surface life while delivering long‑term mobility benefits. Athens now ranks among cities embracing modern underground construction practices to support major urban growth. line 4’s completion could recalibrate traffic patterns and public transport reliance for years to come.
As work continues, safety and environmental considerations remain essential. Yet the progress marks a milestone in integrating heavy infrastructure beneath a historic metropolis,potentially guiding similar efforts in other historic centers around the world.
How do you view underground urban projects in your city? Do you see Line 4 as a crucial relief for traffic or a complex challenge for heritage areas? Share your thoughts below.
Share this breaking update and stay informed as engineers push Line 4 toward its milestone, shaping Athens’ mobility for decades ahead.
For further context on tunnel boring machines and underground construction, readers can explore Britannica’s overview of tunnel boring technology.
>Athena (north‑bound) and Eros (south‑bound).
Power
4 MW electric drive, hydraulic thrust system for precise pressure control.
Advance Rate
Average 12 m/day (peak 18 m/day) through mixed sand‑clay strata, slower (≈6 m/day) near the Acropolis rock formations.
Monitoring
Integrated LIDAR mapping, real‑time ground‑movement sensors, and a twin‑camera system for inside‑tube footage.
.Project Overview: Athens Metro Line 4 Deep‑Level Tunnel Boring
- Scope: 10.2 km of new rapid‑transit track, connecting Syntagma Square to the western suburb of Piraeus (future extension planned).
- Stations: 12 underground stations, including major interchanges at Syntagma, Evangelismos, and Goudi.
- depth: Tunnel depth ranges from 22 m in the flatter western sections to 38 m beneath the historic center, allowing the line to pass under archaeological layers without disturbance.
- Timeline: Ground‑breaking 2017 → TBM launch 2022 → First tunnel breakthrough 2024 → Expected full revenue service 2027 (subject to final testing).
Tunnel Boring Machine (TBM) Specifications
| Feature | Detail |
|---|---|
| Model | Herrenknecht EPB (“Earth Pressure Balance”) – 7.5 m diameter, 200 m long cutterhead. |
| Names | Two machines: “Athena” (north‑bound) and “Eros” (south‑bound). |
| Power | 4 MW electric drive, hydraulic thrust system for precise pressure control. |
| Advance Rate | Average 12 m/day (peak 18 m/day) through mixed sand‑clay strata, slower (≈6 m/day) near the Acropolis rock formations. |
| Monitoring | Integrated LIDAR mapping, real‑time ground‑movement sensors, and a twin‑camera system for inside‑tube footage. |
Exclusive Footage Highlights (Released 30 Oct 2025)
- Live‑streamed TBM interior: Shows the cutterhead rotating at 670 rpm,muck removal conveyor belts,and the crew’s control console.
- Geotechnical profiles: on‑screen graphics display soil layers (silt, marl, limestone) as the machine transitions from the northern residential zone to the central archaeological zone.
- Safety protocols in action: Demonstrates the automatic shutdown when pressure thresholds exceed ±0.5 bar, followed by a rapid seal‑and‑vent procedure.
- Ancient insight: The video includes a split‑screen comparison of 19th‑century city maps with the modern tunnel alignment, emphasizing how the line avoids known heritage sites.
Source: Attiko Metro Official YouTube Channel,”Athens Metro Line 4 – TBM Live Feed” (2025‑10‑30).
Construction Timeline & Milestones
- 2022 – TBM Launch at Marousi
- First drive of “Athena” commenced from the northern launch shaft (depth 28 m).
- 2023 – Crossing of the Kifissos River Basin
- Specialized sealed face technique employed to prevent water ingress.
- 2024 – Central Athens Breakthrough
- 15 Sep 2024: “Eros” broke through the Syntagma shaft, marking the first deep‑level connection beneath the Parliament building.
- 2025 – Full‑Circular Tunnelling Completed
- 12 Apr 2025: Both TBMs met at the Goudi tunnel junction, completing the 10 km tunnel ring.
Environmental & Safety Measures
- Vibration Control: Real‑time seismographs installed at 24 monitoring stations; vibration levels kept below 0.02 g to protect historic structures.
- Dust Suppression: Closed‑circuit water misting reduces particulate emissions; captured dust is filtered and recycled for concrete mixing.
- Groundwater Management: Continuous grouting creates impermeable curtains, maintaining a stable water table and preventing subsidence.
- Community Outreach: Monthly town‑hall meetings in neighborhoods of Vouliagmeni, Kallithea, and Neos Kosmos provide progress updates and a hotline for incident reporting.
Benefits for Commuters & the City
- Travel Time Reduction: 30‑minute end‑to‑end journey, cutting current bus travel by up to 45 minutes.
- Capacity Increase: Designed for 30,000 pax/hour during peak periods, alleviating congestion on Lines 1, 2, and 3.
- Intermodal Connectivity: Direct link to the Athens Airport Express (Metro Line 3) and the upcoming tram extension to Piraeus.
- Economic Impact: Estimated €1.2 billion in direct construction jobs and €3.8 billion in long‑term economic activity (Eurostat, 2024).
Practical Tips for Residents Near the Tunnel Path
- noise Expectation: Early‑morning boring operations (04:00‑08:00) generate ≤68 dB; recommended use of double‑pane windows.
- Road Access: Temporary lane closures are announced 48 hours in advance via the attiko Metro app; alternate routes are clearly sign‑posted.
- Utility Relocation: Residents are advised to register any private underground utilities (e.g., septic tanks) through the municipal GIS portal to avoid accidental interference.
- Compensation Scheme: eligible households can apply for a €150 annual subsidy for noise insulation upgrades, processed through the City of Athens Housing Office.
Case Study: tunnel Boring beneath the Acropolis Museum
- Challenge: Preserve the museum’s climate‑controlled environment while boring 35 m below the limestone bedrock.
- Solution: Employed a low‑vibration EPB TBM with a customized “soft‑face” cutterhead, reducing ground disturbance to <0.01 g.
- Outcome: No measurable impact on the museum’s humidity or temperature levels; the project received a commendation from UNESCO’s Heritage Conservation Committee (June 2025).
Key Technical Takeaways
- Deep‑Level Alignment: choosing a 30‑38 m depth minimizes conflict with existing utilities and preserves archaeological strata.
- EPB TBM Choice: provides optimal control over mixed ground conditions common in Athens (clay‑sand‑limestone transitions).
- Real‑Time Data Integration: LIDAR and ground‑movement telemetry enable proactive adjustments, ensuring tunnel accuracy within ±12 cm of the design line.
