How Long-Haul and Subsea Fiber Routes Affect Data Center Site Selection

Long-haul fiber carries traffic between metro areas and regions, often over hundreds of kilometers. These are high-strand-count cables, usually in buried conduit, built along continuous rights-of-way. The most common corridors are railroads, interstate and state highways, pipelines and electric transmission lines, because each offers a long, controlled path with a single or small number of owners.

Because light weakens over distance, long-haul routes need in-line amplifier sites at intervals along the path, commonly somewhere in the range of 60–100 km depending on the system design. These small buildings or huts hold power and optical equipment. They are also natural places where a route can be accessed, which is one reason a cable passing a site does not mean the site can connect to it.

Our fiber connectivity guide covers the basics of route types, diversity and laterals. This guide focuses on the regional and global layer.

For latency-sensitive colocation and cloud sites, metro fiber and proximity to interconnection hubs usually matter most. Long-haul routes matter most for sites outside major metros, which is where many large power-driven campuses end up. A remote campus needs high-capacity, diverse paths back to the hubs and regions it serves, or it cannot be used regardless of how much power it has.

The shift toward large, remote AI campuses has made long-haul access a real screening criterion rather than an afterthought. See AI data center site requirements and the tradeoffs in near-metro vs. remote power-rich sites.

Light in fiber covers about 200 km per millisecond, which works out to roughly 1 millisecond of round-trip time for every 100 km of route. Long-haul routes rarely follow a straight line. A rail corridor may bend around terrain, and a route between two cities may detour through a third. The useful number is route distance from the site to each target hub, plus the lateral.

For training workloads, a few extra milliseconds is usually acceptable. For inference, interconnection and cloud regions that pair facilities, it may not be. When a user gives a latency budget, convert it into a maximum route distance and test each candidate site against actual routes, not radius circles.

Diversity at the site boundary is only half the story. Two long-haul routes that leave a site in opposite directions can still converge on the same bridge, mountain pass or city. Natural chokepoints concentrate routes: major river crossings, narrow valleys, and the approach to large metros. A single event at one of those points can cut several routes at once.

• Trace each route from the site to its destination hub, not just to the nearest junction.
• Identify shared crossings and corridors, including routes owned by different providers that use the same rail line or bridge.
• Prefer destinations in different metros, or at least different buildings, so one hub outage does not isolate the site.
• Check hazard exposure along each path, such as floodplains, wildfire areas and seismic zones.

Subsea cables carry most intercontinental traffic. Each one comes ashore at a cable landing station, a facility near the coast where the marine cable meets terrestrial networks. From there, terrestrial backhaul routes carry traffic inland to network hubs and data centers.

Siting near a landing station has a few specific considerations:

• Landing stations cluster on stretches of coast with suitable seabed, shore conditions and permitting history, so they are not evenly spread.
• Coastal sites face storm surge, coastal flooding, salt air and, in some areas, hurricane exposure. Our guide to natural hazard risk covers how to screen these.
• Coastal land is often expensive, constrained and subject to additional coastal zone review.
• A new landing involves marine and coastal permits and long lead times, which is a different project from a data center.

For most inland campuses, the practical question is how directly the site connects to the hubs where subsea capacity is handed off, and whether the backhaul from those hubs is diverse. A site does not need to be near the coast to use international capacity.

Large remote campuses sometimes sit far enough from existing routes, or need enough capacity, that a provider builds new long-haul cable to them. That turns fiber into a linear infrastructure project with its own path, schedule and approvals.

• Right-of-way: easements or permits along roads, rail lines, pipelines or transmission corridors, each with its own owner and terms.
• Crossings: railroads, highways, rivers and wetlands, which can require separate agreements and permits.
• Environmental review: a long route can cross species habitat or cultural resource areas, and a federal permit or federal land can trigger federal review.
• Amplifier sites: small parcels along the route for equipment huts, with power.
• Commitment: providers usually want a committed anchor customer before building.

Projects that pair power and fiber along a shared corridor, such as a new transmission line, can sometimes simplify this, but the agreements are separate and the timing rarely lines up on its own.

1. 01List the user’s target hubs or regions and its latency budget, if any.
2. 02Map long-haul routes within a reasonable distance and identify the owner of each.
3. 03Find known access points and amplifier sites on each route, and ask owners where new access is possible.
4. 04Measure route distance to each target hub and convert it to round-trip latency.
5. 05Trace each path for shared chokepoints and hazard exposure.
6. 06If new construction is needed, sketch the corridor, crossings and landowners, and ask which providers would build.

When we screen remote sites, long-haul access is checked alongside power, because the sites with the most power available are often the ones farthest from existing high-capacity fiber.