Turnouts should not be placed opposite each other but should be at least ______ meters apart.

Turnouts, which are points where a track diverges from one line to another, require a certain minimum spacing to ensure safe and efficient operations. The correct answer of 30 meters is based on operational safety and the need to maintain adequate separation between turnouts to avoid conflicts in movement and reduce the risk of derailment or accidents.

Placing turnouts too close to each other can complicate train movements, increase the risk of human error during switching, and lead to potential mechanical issues. The 30-meter separation allows trains enough room to maneuver safely, especially considering the dynamic forces at play during switching operations and the potential for overlapping train paths. This spacing is particularly important in high-traffic areas where congestion is more likely.

In contrast, the other given distances either do not provide sufficient separation for the factors mentioned or may be overly cautious. Adhering to the 30-meter guideline aligns with standard operational practices recognized in the field of civil engineering and rail operations.