Highway design basis: Modern highway geometric and pavement design considers multiple vehicle-related parameters. Which of the following set best represents the core vehicle parameters used (in combination with traffic and environmental inputs)?

Introduction / Context:
Highway design does not rely on a single vehicle parameter. Instead, it integrates several vehicle characteristics with traffic, climate, and subgrade inputs to arrive at safe and durable geometric and pavement designs. Recognizing these parameters helps explain why standards specify lane widths, turning radii, load repetitions, and pavement layer thicknesses.

Given Data / Assumptions:

• The options list major vehicle-related parameters relevant to design.
• Question asks which are used for design (not which one parameter dominates).
• Applies to both geometric elements (e.g., curves, intersections) and pavement thickness design.

Concept / Approach:

Pavement thickness is mainly governed by axle loads (magnitude), axle configurations/spacing (load repetitions and damage), and traffic spectra. Geometric design (turning, layout, clearances) depends on wheelbase, track width, and overall length. Therefore, all listed parameters contribute to some aspect of design.

Step-by-Step Solution:

Verification / Alternative check:

Standard design guides compile vehicle design templates (overall length and wheelbase) for intersections and curves, and axle loading spectra for mechanistic-empirical pavement design—confirming the multi-parameter basis.

Why Other Options Are Wrong:

• Axle loads only: ignores geometry and load spacing effects.
• Axle spacing only: does not capture magnitude or geometry.
• Wheelbase or overall length alone: cover turning geometry but not structural design.

Common Pitfalls:

• Assuming one parameter (e.g., axle load) governs all aspects; geometry still needs length and wheelbase.

Final Answer:

All the above.