A £205M upgrade of the M1 between junctions 28 at Mansfield and 31 at Worksop has been completed.
The final phase went live today and the hard shoulder has been permanently converted to an extra lane, despite concerns about the safety of hard shoulder conversions.
The smart motorway section includes variable speed limits.
Highways England says a similar scheme on the M25 has been running for a year and journey times have been shortened and collisions reduced by a fifth.
Highways England senior programme manager Andy Kirk said: “The new smart motorway will tackle congestion and improve journey times for the thousands of drivers who use it every day.
“The hard shoulder has been permanently converted to an extra lane to significantly increase capacity, and we’ll keep vehicles moving using variable speed limits.”
If there is an incident, lanes will now be closed by using a red “X” on the overhead signs. There are also 20 emergency refuge areas.