The actual speed of a particle or vehicle is the local conversion of duration and distance, that is, local time and space. The potential speed of a particle or vehicle is a characteristic speed for similar particles or vehicles. This characteristic speed is a default speed, to be used if the actual speed is not known.
A characteristic speed may be a local default speed, that is, relative to a specific particle or vehicle and not necessarily applicable elsewhere. A characteristic speed may be relative to someone’s viewpoint, perhaps the way they drive or an estimate of the amount of congestion. A characteristic speed may be a universal speed, an absolute for all particles and vehicles, and so for time and space in general. In any case, an actual speed over-rides any default speed.
A signal speed used in determining the location or velocity of a remote particle or vehicle is similar to a characteristic speed. It is as if a generic particle or vehicle were used to bring the news of what actually happened. This speed might be known but if a generic service is used, then the characteristic speed would be the signal speed.
A characteristic speed may be the typical speed, which may be subject to change, or a maximum speed, which may never change. There are advantages and disadvantages in either case. If the characteristic speed is the typical speed, then it errors are minimized if it is substituted for an unknown actual speed. If the characteristic speed is the maximum or optimum speed, then it shows the extreme case, which may bound the problem.
The speed of light in a vacuum is a maximum or perhaps optimum speed. A typical speed may be the average speed from some speed data or a nominal speed in round units. The specific medium may set the default speed, for example, if the medium is air and sound is used for signaling, the speed of sound may be the logical characteristic speed. For a specific particle or vehicle type, their typical or optimal characteristics may be decisive for the characteristic speed.