Design of tank wagons for steep mountainous routes For mountainous regions with steep road gradients, the bottoms of liquid-carrying wagons should be arranged:

Introduction / Context:
Liquid cargo vehicles must minimize sloshing and spillage when traversing steep grades. The free surface of a liquid at rest is horizontal; tank design should take advantage of this to maintain safe headspace and predictable pressure distribution.

Given Data / Assumptions:

• Vehicle moves at low acceleration relative to gravity (quasi-static on slopes).
• Goal: maintain safe clearance and avoid unintended overflow through vents.

Concept / Approach:
In hydrostatics, the free surface aligns with the equipotential—horizontal in the Earth’s gravitational field. If the tank bottom is parallel to the horizontal plane, the geometry of the headspace and structural supports remains consistent regardless of road gradient, improving safety and capacity utilization. If the bottom follows the road slope, the liquid surface intersects the tank differently uphill vs downhill, risking poor utilization and unbalanced loads.

Step-by-Step Reasoning:

Verification / Alternative check:
Field practice and codes often require level bottoms or internal arrangements that assume a horizontal liquid surface for capacity markings and pressure calculations.

Why Other Options Are Wrong:
Bottom parallel to road surface will alternately reduce or increase effective headspace; deliberately tilting up or down with the direction of motion is impractical; “parallel to chassis” is ambiguous.

Common Pitfalls:
Ignoring dynamic accelerations and braking; baffles are still needed even with level bottoms.

Final Answer:
parallel to the horizontal (level) plane