Final answer:
Upon seeing the sign "Slow down for men working ahead", you should slow down and proceed cautiously for the safety of both the workers and motorists. Reduce speed immediately, and return to normal highway speed only after passing the worksite and ensuring the road is clear.
Step-by-step explanation:
When encountering the sign "Slow down for men working ahead", the correct action one should take is to slow down and proceed cautiously, as there are men working ahead. This ensures the safety of both the workers and those within the vehicle. It's not merely a suggestion; it's a warning that work is being carried out near the roadway, and thus extra caution is required. Upon seeing this sign, one should immediately reduce speed and be prepared for potential instructions from a flagger or altered traffic patterns.
After passing the worksite, ensure the road ahead is clear and you are past all the workers and their equipment before gradually returning to normal highway speed. It is important to stay vigilant for any additional signage that could indicate further changes in roadway conditions or speed limits beyond the work zone.