The event, which is being held at Burghley Park from 4 to 7 September, attracts more than 140,000 people over the course of the four days.
The Highways Agency is working in partnership with the event organiser and local authorities to help get traffic to and from the horse trials and keep traffic flowing. Anyone travelling through the area is however, advised to allow extra time for their journey, or to plan an alternative route or time.
During peak periods there will be slip road closures on the A1 northbound and southbound exit slip roads leading to the B1081 Old Great North Road, just north of Carpenters Lodge junction. This will be in place between 7am and midday from Thursday, 4 September to Sunday 7 September. They will also be implemented from 2pm and 8pm on each day, except Saturday 6 September which will end at 9pm.
There will also be a 50mph speed limit in place throughout the duration of the Horse Trials.
Andy Shilliday, Highways Agency Routine Maintenance Delivery, said:
The slip road closures will only be implemented to relieve traffic flow on the A1 and will be monitored and removed as soon as traffic flows reach an acceptable level.
The temporary mandatory speed restriction, slip road closures and diversion routes will be clearly signposted throughout the event.
We expect traffic to be busier in the area throughout the weekend and we strongly advise road users in the area to plan ahead and allow extra journey time in case of any delays.
Members of the public should contact the Highways Agency Information Line on 0300 123 5000.
Journalists should contact the Highways Agency press office on 0844 693 1448 and use the menu to speak to the most appropriate press officer.