Design speed as a control – principles for geometric consistency Which statements about the role of design speed in geometric design are correct?

Introduction / Context:
Design speed is the foundational parameter that governs the selection of curve radii, sight distance, super-elevation, and other geometric elements. Consistency in design speed enhances safety and driver comfort by aligning user expectations with road geometry.

Given Data / Assumptions:

• A homogeneous highway section is under design.
• Ruling design speed is applicable to terrain and functional class.

Concept / Approach:
Most geometric parameters are functions of design speed. To promote consistency, the design speed should remain uniform over stretches of similar context. If reductions are necessary, they should be gradual and signaled; abrupt changes can surprise drivers and cause crashes.

Step-by-Step Solution:
Confirm that features are sized for the ruling speed → correct.Uniformity of design speed along a route of similar environment → preferable.Avoid sudden design speed drops; provide transitions and warnings → principle of consistency.Therefore, all statements are valid.

Verification / Alternative check:
Consistency checks in design software evaluate speed-profile variations; guidelines call for minimizing unexpected reductions.

Why Other Options Are Wrong:
None; each component reflects accepted practice.

Common Pitfalls:
Mixing urban and rural design speeds within short distances; not coordinating posted speeds with geometric capability.

Final Answer:
all the above