The fatal crash on the M1 in Bedfordshire on Saturday happened on a section of hard shoulder that is sometimes used as a live lane, it has been confirmed.
However, the Highways Agency said the hard shoulder was not a general running lane at the time of the collision, which left three men dead and another seriously injured.
The incident happened on the northbound M1 between junctions 12 and 13, part of the smart motorway network, where the hard shoulder can be brought into general use to reduce congestion.
Police continue to appeal for witnesses to the accident, which happened at 6.46am on Saturday 14 February and left the road closed for several hours.
A coach driver was arrested on suspicion of causing death by dangerous driving, before being released on unconditional bail to return to police in May.
The driver of an Audi A3, a London man in his late 50s, died, as did two of the three passengers, all of whom were men in their 20s from Buckinghamshire. Police said the Audi was stationary on the hard shoulder at the time of the collision.
The third passenger was taken for surgery at the John Radcliffe Hospital in Oxford.
No-one in the coach, which was travelling from Kent with a group of 60 women and three men, was hurt.
The Highways Agency is helping police with their investigation into the incident, and no cause has yet been established.
Unrelated to this specific accident, the Agency has previously raised concerns about the public’s understanding of smart motorway traffic signals.
A road survey published by the Agency last week showed that a third of road users did not know what to do when they saw a red ‘X’ sign - which is commonly used to indicate that a lane is closed.
In November last year, a Red X sign was set over lane 1 on a section of the M25 for 10 minutes to allow recovery of a broken down light goods vehicle yet 145 vehicles were observed on CCTV failing to comply with the sign, risking a collision.
Drivers should never use the hard shoulder for general running unless specificly directed to do so.