Situation based under speed for a predictive cruise control

A computer-implemented method for controlling speed of a first vehicle, the method comprising:

• controlling, by a processor device of a computer system, a prime mover of the first vehicle to operate the first vehicle at a target set speed,
• determining, by the processor device, a rear traffic condition indicating whether there is a risk of being overtaken by a second vehicle travelling behind the first vehicle,
• determining, by the processor device, a topography of an upcoming road to be travelled by the first vehicle, and
• reducing, by the processor device, the target set speed of the first vehicle from a nominal set speed, said nominal set speed being the current speed of the first vehicle, to a reduced set speed, in response to the topography indicating a descending road condition and the rear traffic condition not indicating a risk of being overtaken by the second vehicle before arriving at the descending road condition.