Network Rail’s much-delayed £1.7bn technology trial of the GSM-R unified communications system is at the half-way point.

Pilots began in Strathclyde in October, but the scheme has been plagued by delays and is not forecast to be fully rolled out until 2013.

The rail operator also had to re-assess the system after it emerged it could become overloaded at busy intersections.

But the pilots are proving helpful, said Network Rail programme manager John Collins.

"Trialling the system in a limited area meant the changes did not cause much impact,” he said.

The UK part of the European Rail Traffic Management System, a continent-wide safety system, will run on the GSM-R network.