Everyone should take care when slowing to 40km/h and avoid braking suddenly.
On a road above 80km/h, if it is unsafe for you to slow down to 40km/h you must slow down as safely as you can. If a heavy vehicle is behind you or in front of you, take care by braking gradually and make sure there is plenty of time for the heavy vehicle to slow down as well.
Remember to focus on the task of driving while slowing down and avoid being distracted by the incident on the side of the road.