Final answer:
Farm equipment typically travels at speeds lower than highway speed limits due to safety and design considerations. During the 1970s oil crisis, speed limits on highways were around 90 km/h for efficiency.
Step-by-step explanation:
When transitioning from rural highways onto a highway or freeway, farm equipment often travels at its maximum allowable speed. The maximum speed of farm equipment is typically much lower than the speeds maintained by other vehicles on highways. While discussing ideal speed, it's important to consider that this speed refers to the maximum safe speed at which a vehicle can turn on a curve without the aid of friction between the tire and the road. In the case of farm equipment, however, their design and functionality dictate that their speeds are much lower, primarily for safety and efficiency reasons.
During the 1970s oil crisis in the United States, maximum speed limits on highways were set at about 90 km/h (55 mi/h) to save fuel because over 50% of a car's power is used to overcome air drag at highway speeds, and the most fuel-efficient cruising speed is about 70-80 km/h (45-50 mi/h). It is safe to assume that farm equipment would travel at speeds significantly lower than these limits. Therefore, on rural highways, farm equipment would likely travel at the lower end of highway speeds, which could be further reduced depending on the type of equipment and local regulations.