The phrase "a relatively higher speed" is correct and usable in written English.
It can be used when comparing speeds in a context where one speed is higher than another, but not by a large margin.
Example: "The new model operates at a relatively higher speed than its predecessor, improving overall efficiency."
Alternatives: "a comparatively faster speed" or "an increased speed relative to".
Athletes finishing in the first 25% of all finishers ran the first two 5-km segments at a relatively lower speed than athletes in the second to fourth 25% of all finishers but at a relatively higher sped after km 35.
Torque from the gas engine peaks at a relatively high speed, while diesel engines generate maximum torque at low r.p.m., so there could be a personality clash when diesels and electric motors meet.
Sony says that to get ideal picture quality, a consumer should have an Internet connection that is at least 3 megabits per second, a relatively high speed in most homes, and that could be viewed as yet another drawback to the Bravia Link.
Ismay was widely reviled for having entered a lifeboat rather than going down with his ship; worse, perhaps, it seems to have been he who pressed the Titanic's experienced captain, E. J. Smith, to maintain a relatively high speed even though the ship had been receiving ice warnings.
The second sub-event ruptured at a relatively high speed of 2.78~4.70 km/s.
In this mode, robot can move at a relatively high speed and get over low-height obstacle.
The total rupture duration was approximately 60 s, and the rupture propagates at a relatively high speed of approximately 3.0 km/s.
The vehicle would drift out if the vehicle steers severely at a relatively high speed because of limitation of the lateral tire force.
For example, for a channel with many reflectors, with no line-of-sight (LOS) component, and with a relatively high speed of the users, a Rayleigh channel model will give a good estimate of the distribution of the channel gain.
