A radio system for train drivers recommended after the Paddington rail crash has been delayed by five years.
Safety measures were suggested after the crash in 1999
The system, allowing signallers to speak to a number of drivers at the same time, will be delayed from 2008 to 2013 - 14 years after the crash.
It was a safety measure recommended after the crash between two trains in 1999 in which 31 people died after a driver went through a red light.
The Paddington Survivors Group said it was disappointed by the delay.
The delays in what is known as the GSM-Radio system had come about because the initial timescale was too optimistic, Network Rail said.
About 10,000 miles of cables need to be laid and 2,000 masts need to be put up for the network to work, a spokesman said.
"A realistic timescale has been set for this massive project," he added.
The survivors group was critical of the delay and warned it could put lives in danger.
"Given that serious rail crashes have occurred on average every two years, the probability is that there will be four or five major crashes before this communication system is in place.
"Surely that risk is enough to make Network Rail reconsider this 'money before safety' decision."
The radio system would be more reliable than the existing one and allow better communication between signallers and drivers.
It would also carry data for a new computerised control system aimed at making the network safer. The computer system will not be in place until 2015.
Network Rail denied the current system in the south of England would have to share frequencies with outside users.
This is something Ofcom, which regulates the communications industry, says it will not allow.
Earlier this week Thames Trains was fined a record £2m over health and safety breaches leading to the crash.
The Old Bailey ruled it had failed to properly train its driver who passed a red light at Ladbroke Grove in west London colliding with a First Great Western train.