Legal gross load versus axle spacing – empirical relation If L (metres) is the distance between the extreme axles of a vehicle, the maximum permitted gross load (in kilograms) should not exceed which of the following expressions?

Introduction / Context:
Highway regulations often limit a vehicle’s gross load as a function of axle spacing to control pavement and bridge damage. Empirical relations are used to reflect how load spread improves with larger axle spacing.

Given Data / Assumptions:

• L = spacing between extreme axles (m).
• Gross load limit expressed in kilograms.
• We are to identify the correct empirical expression among the choices.

Concept / Approach:
Such relations typically combine a linear increase with spacing (improved load distribution) and a small quadratic penalty (to limit runaway growth and reflect structural effects). The commonly cited form uses constants 1525 and 6.3 with a quadratic term 14.7 L^2.

Step-by-Step Solution:
Match the standard constant set to the given alternatives.Select 1525 (L + 6.3) - 14.7 L^2 as the consistent formula.

Verification / Alternative check:
For moderate values of L, the resulting gross load falls in realistic ranges for multi-axle vehicles; alternatives with altered constants produce inconsistent regulatory limits.

Why Other Options Are Wrong:
They change the intercept or slope constants or use a different leading coefficient, which do not correspond to the standard empirical relation.

Common Pitfalls:
Applying the formula without units; forgetting that bridge-specific postings may further restrict the value.

Final Answer:
1525 (L + 6.3) - 14.7 L^2