A tunnel system is a huge positive for commuters, and the main reason why so much money, time and energy is spent setting up conveyor belts, tunnel boring machines and prefabricated concrete panels is because of just how much time and money is saved on travel.

This was the justification for High Speed 2, the Channel Tunnel, the Gotthard Base Tunnel and the currently under-construction Fehmarnbelt between Denmark and Germany. Tunnels cut travel times typically cut emissions and are typically adored by commuters.

In fact, for rail tunnels in particular, there is only one universal frustration with the tunnel experience, and that is the potential they have for creating wireless dead zones.

This is such a concern that Vodafone has commissioned a new type of mobile antenna specifically designed to be installed in tunnels to try and fix the problem.

What are dead zones, why do they form in tunnels and why is it important to try and consign them to the past?

What Is A Dead Zone?

A dead zone is any area or situation where it is impossible to get a mobile phone reception despite a carrier covering that particular area. 

This is different from a Faraday cage, a structure designed to block wireless and electromagnetic signals because they are an unintended side effect of the construction process and are also often undesirable.

Why Are They Caused By Tunnels?

It is typically caused by heavy-duty construction materials and geographic obstacles, both of which are a major part of tunnel construction because the wireless signals struggle to permeate through layers of dense concrete and metal.

A lot of larger buildings can create small pockets of wireless dead zones, but because the zones are so small, people generally are not in the same place long enough for it to cause an issue.

This is different with tunnels, which can leave a commuter without a signal for several minutes or more at a time depending on where they are and the type of wireless device they have.

Why Are They A Problem?

Ever since the mobile phone became popular in the late 1990s, it was grudgingly accepted that phone calls would drop, and any work that was being done on a laptop would need to be done offline.

However, with commuters often working whilst on the tunnel and even holding meetings via video conferencing apps, the need for a fast, stable internet connection is more widespread than ever.

However, as many people rely on their phones to keep them safe and in contact in case of an emergency, if there was a disruption that trapped people in a tunnel for a considerable length of time, it could potentially cause a major issue.

This is a problem that lift operators have needed to navigate as landline-based emergency phones have needed to be replaced with battery-supported alternatives.

What Are The Solutions?

Because this is a widespread concern and a lot of people are keen to close the coverage gaps, there are a lot of proposed ways to get around tunnel dead zones.

One is Vodafone’s solution to fit new-generation antennae into tunnels. Just five of them were enough to cover the 1400-metre Arlinger Tunnel project, although they needed to be designed to be robust enough to handle the wind tunnel vibrations.

Smaller tunnels can typically get away with fitting antennae at the start and the end, avoiding this issue entirely, but signal repeaters are typically a necessity and for modern tunnel projects may be factored into architectural decisions from day one.

A similar system is being deployed throughout the London Underground network, which whilst a shorter coverage area is complicated by the centuries-old tunnel system and the additional challenges that this inevitably causes.

Alternatively, some railway operators work with mobile operators to install signal boosters onto trains directly, which can help with reception for particular routes, although this can cause problems if multiple railway operators use the same line and come across the same problem.

As well as this, many phones offer wifi calling and many railway operators opt to set up a wifi connection. Whilst this can lead to an additional charge for commuters, it does mean that as long as the wifi itself is not disrupted, calls, texts and online services can continue.

For other types of tunnels and services such as GPS applications used on the road, one innovative solution involves connecting devices together in a type of peer-to-peer network that at some point connects to the outside world.

With ever-improving wireless technology such as 5G, it is possible that tunnel dead zones could be history, but it will require some coordination to find the right solution for each tunnel.