Answer-first: A single mobile cell realistically carries only a few hundred connected devices at once — so when tens of thousands of people gather, or an incident makes everyone call at the same moment, the network saturates exactly when you need it. On 7 July 2005 in London, one operator’s call volume jumped 250% and its network hit capacity by 10am. Broadcast-based crowd communication, which reaches every screen on site over its own signal, keeps working when the mobile network does not.

How little capacity a mobile cell really has

A mobile mast is not a bottomless pipe. Telecoms engineer and author Martin Sauter puts realistic 4G numbers at roughly 250 devices attached per sector, of which only about 60–100 are actively connected at any one moment. In pure theory a cell can hold over 1,000 connections, but operators set the limit far lower because beyond that nobody gets a usable speed. His conclusion about crowds is blunt: stadiums need lots of small cells because a normal mast simply cannot cope. Bring 20,000, 50,000 or 80,000 people into range of a handful of masts and the maths breaks long before everyone is connected — which is why your phone shows full bars yet calls and data still fail.

What that looks like in a real crisis

The clearest UK example is the 7 July 2005 London bombings. According to the London Assembly’s official Report of the 7 July Review Committee and contemporary reporting:

• Vodafone’s call volume rose 250% and text volume roughly doubled; its network reached capacity at about 10:00am and it invoked access overload control (ACCOLC).
• O2 carried about 11 million calls that day, against a normal 7 million — roughly 60% more — not counting the calls that never connected.
• Cable & Wireless handled around 300,000 calls every 15 minutes, against 30,000 normally — about ten times the load.
• Police asked O2 to restrict the network to emergency use within 1 km² around Aldgate for four hours. As the academic explainer “When the phones went dead” records, it was only partly successful — some emergency responders’ own phones were blocked too.

It is not a uniquely British problem. On 11 September 2001, cellular traffic across New York and the US east coast roughly doubled and networks crashed. The pattern is always the same: the moment a crowd most needs to be reached is the moment the network is least able to carry it.

Networks are built for typical demand, not simultaneous demand

This is by design, not a fault. As the same analysis explains, networks are designed to cope with typical traffic demands — there simply isn’t enough capacity for everyone to use them at once. And we lean on them more than ever for safety: in 2023, 79% of the UK’s 41.9 million 999 calls were made from a mobile. A safety plan that assumes the mobile network will be there in a mass-casualty moment is planning around the one system most likely to fail under exactly those conditions.

“Cells on wheels” are a patch, not a guarantee

Operators do deploy temporary masts, small cells and distributed antennas at big events. They help — but they mostly relieve low-bandwidth texts and voice, not the instant, guaranteed, site-wide reach a safety procedure needs, and they still depend on the congested public network behind them. Even the engineer’s verdict above is that proper event coverage means dense in-venue small cells, not a couple of extra masts.

What actually keeps working

This is the gap we close. Our technology — for which a European patent application is pending — drives video and audio independently over its own broadcast signal, with no reliance on mobile networks, public IP networks (which can be targeted) or cabling. Because it does not depend on those networks, it keeps working precisely when they are overloaded or down. From a central control room, an operator switches every HIKER LED screen across the site to the same clear instruction at once — no app, no signal and no phone-in-hand required from a single visitor.

What this means for Martyn’s Law

Under Martyn’s Law, communication is a named public protection procedure. If your communication plan depends on visitors’ phones or an app, you are depending on the system the numbers above show fails first under crowd or incident conditions. A broadcast-based layer that reaches the whole crowd independently of the mobile network is exactly the kind of tested, real-time capability the duty calls for.

Frequently asked questions

How many people can one mobile mast actually serve at once?
Far fewer than people assume. Realistic 4G figures are around 250 devices attached per sector and only about 60–100 actively connected at any moment; the theoretical ceiling of ~1,000 is never used in practice because speeds collapse. A crowd of tens of thousands overwhelms a handful of masts quickly. (source)

Why does my phone fail at concerts and festivals even with full signal?
Full bars mean your phone can see the mast, not that the mast has room to carry your call. With thousands connecting at once, the cell saturates, new connections are refused and bandwidth is split thin.

Did mobile networks really fail in a real emergency?
Yes. During the 7 July 2005 London bombings, one operator’s call volume rose 250% and its network hit capacity by 10am, and emergency-only restrictions had to be imposed around Aldgate. (London Assembly report)

How does CrowdCows reach everyone if the mobile network is down?
We broadcast video and audio over our own signal — steered independently, with no mobile network, no public IP and no cabling — so every screen on site shows the same instruction at the same time, regardless of network congestion. (European patent application pending.)

Sources

• Martin Sauter (WirelessMoves) — LTE and the number of simultaneously connected users
• London Assembly — Report of the 7 July Review Committee (June 2006)
• The Conversation — When the phones went dead: 7/7
• Communication during the September 11 attacks
• 2023 UK 999 call statistics (79% from mobile, 41.9m calls)

Read the Martyn’s Law & crowd communication guide or talk to us about your venue.