What speed could a train operate at when passing an approach block limit sign with a K-card for that block?

When a train approaches a block limit sign marked with a K-card, it indicates that the train has clear signals to proceed into that block. The K-card signifies a specific condition where the train's crew is aware of the signals and the block ahead. As a result, the train can operate at the maximum authorized speed for that section of track, provided that all other conditions and rules are met. This means the train is permitted to proceed at the speed limit established for that area, which is typically designed to ensure safety and efficiency.

Operating at maximum authorized speed is contingent upon having adequate control and the train being in compliance with safety requirements. This option reinforces the idea that under the correct conditions, including the presence of a K-card, trains are expected to utilize their full operational capability.