Princess Road and Princess Parkway in Manchester will be lowered from 40mph to 30mph for an 18-month trial after a proposal was approved by councillors.
There have been two deaths and 84 crashes over the past three years.
A friend of Ian O'Mara, who died when he was hit by a coach on a pelican crossing in 2015, helped set up a petition to change the speed limit.
A coach driver who hit the dog walker in Princess Road was given a suspended sentence after admitting causing death by careless driving.
The change to the speed limit was passed by Manchester City Council on Wednesday, although a date for when it comes into force is yet to be confirmed.
Princess Parkway merges into Princess Road and stretches 3.7 miles (6km).
Campaigner Sam MacWilliam, from Chorlton, said: "The road is very important for people coming into the city, but they need to understand that they are coming off the motorway and into an area where people live.
"There are schools and churches here."
The speed limit on a major route into a city has been reduced following a campaign launched after a man's death.