What type of train handling technique is critical when traversing steep grades?

When traversing steep grades, employing controlled and regulated brake pipe reductions is essential for maintaining optimal train handling. This technique involves making gradual and measured adjustments to the brake pipe pressure, which allows the engineer to manage the train's speed effectively without causing excessive strain on the braking system or risking a loss of control.

By using controlled brake pipe reductions, the engineer can create a balance between the train's momentum and braking forces, preventing the train from gaining too much speed on downhill stretches. This strategy helps avoid the risk of over-stressing the brakes, which can lead to overheating and potential failure, as well as reducing the likelihood of a runaway train scenario.

In contrast, utilizing maximum throttle consistently or making frequent and large brake pipe reductions can lead to unstable train handling. Maximum throttle can increase the risk of gaining excessive speed, while abrupt brake reductions can lead to jerky movements, adversely affecting the train's balance and potentially leading to safety concerns. Additionally, removing all retaining valves would eliminate critical safety features that support braking on downhill grades, further compromising train control.

Overall, controlled and regulated brake pipe reductions provide the most effective and safest method for managing a train on steep gradients, allowing for smoother operations and enhanced safety.