A range of issues are impacting mobile radio frequency, resulting in subpar wireless coverage and internet connections for rail commuters.

Signal performance is influenced by the rolling stock’s insulation, the loading of trains and design factors.

A subsequent report by the same team to investigate mobile signal connectivity in tunnels is due to be published by DfT in 2022.

Transport advisors at FCP, alongside engineering firms Arup, Aecom as well as technology partners Realwireless and LS telecom, investigated concerns raised by the UK’s Department for Transport about poor mobile connectivity for passengers using rail services in the United Kingdom.

The reliability of on-board internet connectivity is measured in the bi-annual National Rail Passenger Survey conducted by Passenger Focus, a government-funded agency that represents the interest of passengers.

UK rail passengers dissatisfied with wifi and mobile coverage

In this 2020 National Rail Passenger Survey by Transport Focus, Britain’s independent watchdog representing the interests of Britain’s rail passengers, 48% of passengers said they were dissatisfied with internet connectivity, while 37% were satisfied and 15% were neutral.

Dissatisfaction rates were much higher for some individual train operators, including 62% dissatisfaction among customers of South Western Railway and Thameslink services, and 59% dissatisfaction among those travelling on the Merseyrail network, with a similar figure for local services in the West Midlands.

62% of passengers using South Western Railway services dissatisfied with internet connectivity.

Levels of satisfaction were higher on long-distance routes. London North Eastern Railway (LNER) had a 59% satisfied score, with 55% for Hull Trains, while Avanti West Coast recorded 50% satisfaction and the Great Western Railway recorded 48%. The lowest level of satisfaction for services in this category was recorded by East Midland Trains at 32%.

Study to understand train signal attenuation

Since satisfaction differed by train type, route and other factors, a deeper study was required to understand the underlying reasons for train signal attenuation, which refers to the loss of signal strength due to external or internal factors between the base station and the built-in antennae of passengers’ mobile devices.

The study revealed that signal performance is influenced by several factors, including the design characteristics of the vehicle, the angle of signal arrival, the location of the passenger within the train and the effect of loading (both passenger crowding and baggage).

Signal attenuation is typically measured in decibels (dB) or voltage and can occur due to a variety of factors. It may cause signals to become distorted or indiscernible. An example of this is wi-fi signal strength getting noticeably weaker the further that your device is from the router.

Wi-fi is not the only carrier, as digital networks increasingly deploy 4G LTR (long-term evolution) and in some cases move to 5G NR (new radio). These are all enhancements to the original global standard adopted in 1991.

The capacity available for mobile devices has increased from 14.4 kilobytes per second for 2G, to 3.1 Megabytes per second for 3G, 200 Megabytes per second for 4G and up to 1 Gigabyte per second for 5G, enabling a full-length high-definition film to be downloaded in 3 minutes.

Rolling stock design and window provision

The study looked at the decibel loss that occurred for different types of coaching stock design given construction and the area occupied by windows. The reduction was less for passengers sitting next to a window, but there were other factors.

For example, although rolling stock built by Siemens Desiro has a greater window area than the Bombardier Electrostar units, the loss of signal strength was considerably greater. This was thought to be the result of higher thermal and acoustic insulation standards for the Desiro units.

The efficient insulation used in Siemen Desiro vehicles is believed to be a cause of vehicle penetration mobile signal loss.

It was believed that poor internet connectivity on the Alstom Pendolino trains operated by Avanti West Coast was due to the glass window specification that resulted in a loss of mobile signal vehicle penetration.

For brick-built buildings and motor vehicles, mobile network operators expect a maximum of 10dB loss in signal strength. Despite increasing this to an expectation of up to 25dB penetration loss for railway vehicles, this figure has been exceeded due to rolling stock design factors and the loading of trains.

A subsequent report by the same team to investigate mobile signal connectivity in tunnels is due to be published by DfT in 2022.