Law and conditions dictate top speed
Your job as a driver is moving from one place to another as rapidly and efficiently as possible—with due regard for safety...your own safety, safety of the vehicle and cargo, and, above all, the safety of the public— any persons who may be using the same public ways. Although the term, “as rapidly as possible” denotes speed, the word “efficiently” must suggest caution. A trip cannot be efficient if it is not safe. To an immature driver, the word, “speed,” might mean “give’er all it's got!” But let's hope we have no such drivers. If you're not all skillful and experienced operators who always use sound judgment about what speed is proper for all situations and under any and all conditions, we face a tough job of coaching and retraining—or weeding out.
You might say speed for driving a motor vehicle of any kind is a relative term. Top speed on the open highway (for good drivers) does not mean the fastest possible with a powerful engine that responds so readily to your gas pedal. Let's repeat that top speed is variable, always a matter for sound judgment. On a good, dry open highway, top speed must never be faster than the law allows—the posted speed limit. If it starts to rain on that beautiful pavement, top speed must be much slower than the posted limit. If a fog rolls in, top speed may seem little more than a crawl—or must be reduced even to zero!
There are many reasons for a driver to decide that reducing speed is smart, aside from weather conditions. The traffic thickens so there is a problem maintaining safe following distance with our dropping back...an irresponsible driver is trying to gain time by weaving in and out of traffic lanes...up ahead there is a farm truck barreling along a side road that intersects the highway...on a superhighway, drivers start cutting across lanes to reach an exit or on a city street there may be children at playing close to the roadway...and many other reasons. Proper speed is a matter of judgment. The driver who does not quickly learn to choose the proper speed limit in any situation may not be driving very long.