MPs and protestors are complaining about the rollout of smart motorways after safety concerns.
Campaigners are recommending that their continued introduction be paused.
Demonstrators are adamant that they should not got ahead and have protested outside parliament.
They carried 38 coffins - which is one for each life lost on smart motorways between 2014 and 2019 - and revealed banners saying "How many more have to die?" and "Still here no thanks to smart motorways".
Highways England revealed that by 2025 an additional 300 miles of smart motorway will be created across the country, but there is real doubt over the safety of them and if they should go ahed.
There are already sections of smart motorway on parts of the M1 , M4 , M5 , M6 , M42 and M62 .
What are smart motorways?
Smart motorways use the hard shoulder as a running lane and speed limits that vary, in order to try and manage congestion.
There are three types of smart motorway: all lane running, dynamic hard shoulder and controlled motorway
Are smart motorways dangerous?
The RAC explained why some drivers are worried about smart motorways.
"Drivers have voiced concerns about sudden variable speed limit changes causing them to slam on their brakes to reduce their speed in time," they said.
There were 38 killed people on smart motorways between 2014 and 2019.
However, the report also noted that the roads have the lowest casualty rates on major English roads.
Tory MP Huw Merriman, who chairs the committee, said: "Looking at the available evidence, smart motorways do appear to be safer than conventional motorways even once the hard shoulder is removed.
"However, this evidence is also open to question. Only 29 miles of these all-lane running smart motorways have operated for over five years.
"It therefore feels too soon, and uncertain, to use this as an evidence base to remove the hard shoulder from swathes of our motorway network."
How do smart motorways work?
All lane running smart motorways covert the hard shoulder into a running lane permanently.
Lane one, that was formerly the hard shoulder, is only closed to the public when there is an accident.
Signs are installed on this section of the motorway to control the speed limit, which can vary.
For drivers that breakdown, there are emergency refuge areas along the sides of the motorways.
Dynamic hard shoulders open extra lane at different points to ease congestion. The RAC said: "On these stretches a solid white line differentiates the hard shoulder from the normal carriageway. Overhead signs on gantries indicate whether the hard shoulder is open to traffic."
Controlled motorway schemes only use the hard shoulder in a 'genuine emergency' and these also have variable speed limits.
