Which action may lead to a bus or motorcoach crash?

The action that indicates a significant risk for a bus or motorcoach crash is not accounting for the size of the gap needed to merge. Merging onto highways or into traffic requires careful consideration of the vehicle's size and the speed of other vehicles. Buses and motorcoaches are larger and have different acceleration capabilities compared to smaller vehicles, meaning they require more space to safely enter the flow of traffic. Failing to properly judge the gap can result in a collision, either by cutting off another vehicle or miscalculating when it is safe to join the lane.

In contrast, driving slowly on highways, while it may not be ideal, is not inherently a crash-causing action. It can be safe if done thoughtfully and within the context of other vehicles' speeds. Always using turn signals is a safe practice that contributes to road safety by informing other drivers of your intentions. Similarly, driving within the speed limit is essential for maintaining control and ensuring safety, reducing the likelihood of an accident. Therefore, understanding the critical importance of proper merging techniques is key to preventing crashes with larger vehicles like buses and motorcoaches.