Ministers are "blatantly ignoring" safety concerns about smart motorways, according to MPs.
The Commons' Transport Select Committee claimed the Government had rejected the "principal recommendations" of its critical report into the conversion of hard shoulders into extra traffic lanes.
The cross-party group of MPs expressed its disappointment that the Department for Transport approved an all-lane running scheme on a 32-mile stretch of the M4 before its response to their report could be considered.
Officials have been keen to press ahead with smart motorway projects - which are already in operation on sections of the M42, M1, M6 and M5 - as a way of boosting capacity without widening roads.
The Government response to the committee revealed that Highways England, which is responsible for managing motorways and major A roads in England, is to review the spacing of emergency lay-bys to reduce the likelihood of cars stopping in live lanes.
MPs said the M4 proposal should not go ahead until this work was carried out.
They also described non-compliance with variable speed limits and Red X signals to indicate lane closures as "deeply worrying".
Labour MP and chairwoman of the committee, Louise Ellman, commented: "The Department for Transport is blatantly ignoring the safety concerns set out in our report.
"We had barely received the response to our report before the Government endorsed an all-lane running scheme on the M4.
"The committee isn't arguing with the Government about the need for more capacity on our motorways, or their statement that motorways are our safest roads. We support smart motorways such as the M42 scheme.
"But we take real issue with the Government's assertion that all-lane running schemes on motorways are no different to other types of roads without hard shoulders.
"Motorways are a different class of road and drivers have different expectations when using them."
She added: "We are not the only people who are worried about this incarnation of all-lane running schemes.
"In the course of our inquiry, there were genuine concerns raised by the emergency services, road workers and recovery operators. The Government cannot ignore them."
RAC chief engineer David Bizley said the "flat refusal" of the Government to listen to genuine voices of concern was "very worrying".
He went on: "The safety case for all-lane running is not yet proven and as a result we fear that it won't be long before there is a major tragedy that will make the Government think again."
AA president Edmund King said: "Four out of five drivers are scared about using emergency refuge areas, some even dubbing them 'death zones'.
"The Government needs to act now to improve this perception."
Transport minister John Hayes said: "We have some of the safest motorways in the world but we are not complacent and are always looking at ways to make them safer.
"All-lane running on the M25 has not only tackled congestion, it has cut collision rates by nearly a fifth and cut casualties by more than a quarter after a year of operation.
"Safety of all road users is our priority and I will ensure that Highways England continues to review all-lane running schemes and take action to improve them further."