Final answer:
The 'detour 1000 ft' sign indicates an upcoming alternate route for vehicles, typically due to road construction or temporary closure. Drivers should follow detour signs to navigate around the obstruction.
Step-by-step explanation:
The yellow sign that says "detour 1000 ft" indicates that there is an upcoming alternate route for vehicles. This is often due to road construction, a temporary road closure, or some other obstruction that makes the usual path impassable or not safe for use. Drivers should prepare to follow detour signs that will lead them around the obstruction and back onto their original route. Despite the presence of this sign, it does not necessarily mean there will be a speed limit reduction; however, drivers should always be cautious and ready to adjust their speed according to the road conditions and any additional signage.