Ferrovial is a large infrastructure‑focused group with very high financial leverage: total debt (including leases) around €22.6 bn against equity of €6.4 bn, giving a debt‑to‑assets ratio of roughly 86 % and net‑debt‑to‑EBITDA of about 17×. Interest coverage is modest (operating profit ≈ €423 m versus finance costs ≈ €320 m), leaving limited margin for error. At the same time the company generates solid operating cash flows (≈ €1 bn in 2023) and holds a large cash buffer (≈ €5.1 bn), providing some liquidity cushion.

The market environment for 2022 shows gradually rising risk‑free rates (5‑year swap average 1.73 %, 10‑year 1.93 %) and investment‑grade corporate bond yields around 1.1 %, while sub‑senior (hybrid‑type) spreads average roughly 2.3 %. This suggests that hybrid bonds can be issued at a reasonable financing cost, albeit higher than senior debt, but still well below the cost of equity.

Hybrid instruments can be treated as equity by rating agencies, improving reported leverage ratios and providing greater financial flexibility without immediate dilution. Given Ferrovial’s already high leverage, adding a modest portion of hybrid debt can help balance the capital structure, reduce reliance on senior secured borrowings, and take advantage of the current low‑rate environment while preserving cash flow coverage.

A conservative approach—matching the industry practice for infrastructure companies—would be to allocate roughly one‑quarter of total debt to hybrid bonds. This level provides meaningful equity‑like credit support without excessively increasing interest burden or refinancing risk in a rising‑rate environment. More aggressive proportions (50 % or higher) would further elevate leverage and could strain coverage ratios, especially if rates continue to climb.

Therefore, a moderate reliance on hybrid bonds of about 25 % of the capital structure is appropriate.

<answer>25%</answer>