The speed limit on the A140 in Suffolk is being cut to 50mph.
Some places on the A14 will be restricted to 40mph or 30mph.
Suffolk County Council made the decision on Thursday for the new limit on the road which connects Suffolk to Norfolk.
It is an experimental speed limit along the entire stretch of the A140 - which has seen 80 people die in road accidents over the last 20 years.
The 50mph limit will be in place for the next 18 months with a view to making it permanent if it is a success in cutting the number of accidents.
As well as that speed limit, a 30mph limit will be imposed between Earl Stonham and Stonham Parva - where the limit is currently 40mph.
At Brome it will be 40mph through the village.
New electronic signs will also go up, which will be activated by cars travelling too close together or too fast.