Final answer:
The speed limit when a highway traffic lane is closed due to construction varies by state or jurisdiction and is typically posted on signage at the construction site. It's essential to follow these speed limits as they are enacted for safety and often carry higher fines for speeding.
Step-by-step explanation:
When all or part of a highway traffic lane is closed due to construction, the speed limit is typically reduced to ensure the safety of workers and drivers. However, the reduced speed limit can vary by state or jurisdiction. For example, in some places, the speed might be set at 45 mph, while in others, it could be 55 mph or another number, always with the possibility of the speed being otherwise posted if local conditions warrant a different limit. Often there are specific construction zone speed limits that are posted on signs at the start of the construction area. It's important to always be alert and follow the posted signs as well as local laws because fines for speeding in construction zones are typically higher to encourage safer driving behavior.