What is the maximum speed allowed over a Class 4 frog with tread wear of 1/2 inch, according to FRA guidelines?

The correct answer is based on the guidelines established by the Federal Railroad Administration (FRA) regarding the operation of trains over frogs, particularly considering the condition of the frog. A Class 4 frog, along with other track components, has specific speed restrictions that relate directly to its maintenance condition.

When the tread of the frog has significant wear, such as 1/2 inch, it indicates the necessity for reduced speed to ensure safe operation and prevent derailments or significant wear and tear on equipment. For a Class 4 switch or frog under these conditions, the maximum allowable speed is set to 10 MPH. This cautious approach ensures that any potential issues resulting from the frog's condition are mitigated through lower operating speeds, promoting safety for both trains and track infrastructure.

While other choices suggest higher speeds, they do not align with FRA regulations, which prioritize safety especially in conditions of increased wear and tear. Therefore, the correct understanding of speed limits in relation to infrastructure maintenance is crucial for safe rail operations.