M4 'smart motorway' safety concerns raised
Safety concerns have been raised over proposals to turn part of the M4 into a "smart motorway".
About 32 miles (51km) between London and Theale, Berkshire, would be widened in both directions to four lanes, using the hard shoulder.
Some motorists and the RAC have said the lack of a hard shoulder would leave motorists in a vulnerable position if there was a breakdown.
The Highways Agency said there would be refuges for broken down vehicles.
Senior project manager Andrew Hitch said converting the hard shoulder into a lane would also discourage motorists from stopping for non-emergencies, such as to answer their phones.
Smart motorways also use a range of new technology, including electronic signs, to vary speed limits in response to driving conditions.
They are managed and monitored by the Highways Agency's regional control centres using CCTV.
Steve Bowles, who regularly uses the M4 for his haulage business, described the lack of a hard shoulder as "scary".
"I want to deliver the cargo safely. I don't want to deliver it in a dangerous way on a dangerous motorway," he said.
Simon Williams, of the RAC, said the permanent use of the hard shoulder as a running lane would put lives at risk.
"The chances of being able to get into a refuge area are reduced because of the spacing between them, which is up to 2.5km," he said.
Similar schemes already operate on stretches of the M25 and M1.
The proposals, which went on public display earlier at Reading's Madejski Stadium, include upgrading or replacing 11 overbridges and five underbridges as part of the £700m project.