Final answer:
Idaho law mandates that drivers maintain a speed that is reasonable and prudent at all times, which may differ from both posted and implied ('de facto') speed limits depending on road conditions and other factors.
Step-by-step explanation:
Idaho law requires drivers to maintain a speed that is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing. This means that drivers should always drive at a speed that is safe for the road conditions, regardless of the posted speed limit. For example, if the speed limit is 35 miles per hour but there is dense fog or it is icy, the reasonable and prudent speed would be lower than the posted limit.
In the scenario provided, Peter, feeling frustrated by the slower vehicle, should remember that the driver ahead of him might be maintaining a speed that he considers reasonable and prudent for his own safety or due to physical limitations that come with age. Although some drivers tend to drive above the posted speed limit, this is not always the safest option, as the ideal speed on roads also depends on factors like visibility, traffic density, and road conditions.
While the term 'de facto speed limit' refers to the speed at which the police are most likely to pull you over, it is important to adhere to the 'de jure speed limit' which is legally posted, unless conditions dictate a need for slower travel. Understanding and abiding by these laws help maintain safety on the road for all users.