To determine the appropriate extent to which Ferrovial SA should issue hybrid bonds, we must analyze its current capital structure, financial performance, and strategic needs in the context of the provided S&P methodology and market conditions.

**1. Current Capital Structure and Hybrid Position**
First, we calculate the "Total Adjusted Capital" to understand the baseline.
*   **Equity (2023-01-01):** 6,354 million EUR.
*   **Debt:** We need to estimate the interest-bearing debt.
    *   Noncurrent Portion of Other Noncurrent Borrowings: 10,776 million EUR.
    *   Noncurrent Debt Securities and Bank Borrowings of Infrastructure Projects: 7,893 million EUR.
    *   Current Borrowings and Current Portion of Noncurrent Borrowings: 877 million EUR.
    *   Current Debt Securities and Bank Borrowings of Infrastructure Projects: 74 million EUR.
    *   *Note:* Infrastructure project debt is often ring-fenced. However, for a consolidated view of leverage pressure on the parent/group rating, we look at the total indebtedness. Total Debt approx = 10,776 + 7,893 + 877 + 74 = 19,620 million EUR.
    *   There are existing "Perpetual Subordinated Bonds" listed in equity movements. The line item "Other Equity Securities" is 508 million EUR (2023-01-01). This likely represents the equity credit portion of existing hybrids or similar instruments. Let's assume the nominal value is higher, but the equity credit is capped. For the purpose of the "15% of total adjusted capital" cap, we look at the ratio of Hybrid Equity Credit to (Equity + Adjusted Debt).
    *   Total Adjusted Capital ≈ Equity (6,354) + Debt (19,620) = 25,974 million EUR.
    *   Current Hybrid Equity Credit: The "Other Equity Securities" is 508 million. If this is fully equity-credited, it represents ~1.95% of Total Adjusted Capital. This is well below the 15% cap.

**2. Financial Performance and Leverage Pressure**
*   **Profitability:** Net Profit attributable to owners was 186 million EUR in 2022, down significantly from 1,198 million in 2021 (which included large fair value adjustments/disposals). Operating profit was 423 million.
*   **Cash Flow:** Cash flow from operating activities was 1,002 million EUR. Cash flow from investing was -732 million. Free cash flow before financing was positive (270 million).
*   **Leverage:** With ~19.6 billion in debt and ~6.35 billion in equity, the Debt-to-Equity ratio is roughly 3.1x. This is a moderate-to-high leverage profile typical for infrastructure/construction firms but suggests pressure on credit metrics.
*   **Refinancing Needs:** The company has significant non-current borrowings (10.7 billion excluding infrastructure projects). The maturity profile isn't explicitly detailed year-by-year, but the volume suggests ongoing refinancing needs. The cash balance is healthy (5.13 billion), providing liquidity buffer.

**3. Strategic Context and Market Conditions**
*   **Business Model:** Ferrovial is transitioning/has transitioned towards a pure-play infrastructure company (spinning off construction). This often involves significant M&A or capital restructuring. The "Investments in Infrastructure Projects" are large (13.6 billion).
*   **Market Data:** The swap curves and bond spreads in 2022 rose significantly compared to 2020-2021. The 10Y swap average went from -0.14% (2020) to 1.93% (2022). Corporate bond spreads (iBoxx) also widened. This means the *cost* of issuing new hybrids is higher than in previous years.
*   **Guideline Application:**
    *   **0%:** Incorrect. There are refinancing needs and leverage is not "low".
    *   **3.75%:** This implies "mild leverage optimization" and "limited rating flexibility". Given the drop in net profit and the high absolute debt load, Ferrovial likely needs more than mild optimization to maintain or improve its investment-grade rating, especially if pursuing growth/M&A.
    *   **7.5%:** This implies "moderate refinancing/acquisition needs" and that issuance "meaningfully improves adjusted leverage metrics". With existing hybrids at ~2% of capital, moving to 7.5% allows for ~1.4 billion EUR in new hybrid equity credit (approx). This is a manageable issuance size (<3bn cap) that would strengthen the equity base, lower reported leverage ratios (Debt/EBITDA, FFO/Debt), and provide cushion against earnings volatility (seen in the 2022 drop). It balances the higher cost of debt in 2022 with the need for structural subordination.
    *   **11.25% / 15%:** These levels are for "high capex intensity," "significant leverage pressure," or "material downgrade risk." While Ferrovial has debt, its operating cash flow is positive and covers interest (Interest paid 329m vs Operating Profit 423m + Depreciation 299m). It does not appear to be in distress or facing an imminent downgrade that *requires* maxing out hybrids. The cost of hybrids in the current rising rate environment (10Y swap ~1.9% + spread) would be material. Issuing up to 15% would significantly increase the weighted average cost of capital without a corresponding crisis-level need.

**Conclusion:**
Ferrovial has a moderate leverage profile and is in a phase of strategic focus on infrastructure. The drop in 2022 earnings highlights the benefit of strengthening the equity buffer. However, the company generates solid operating cash flow and holds significant cash. It does not face the extreme distress or transformational M&A scale that would justify the highest tier (15%) given the high cost of capital in 2022. A move to **7.5%** represents a balanced approach: it meaningfully improves leverage metrics and provides rating headroom for future infrastructure investments or acquisitions, without over-leveraging the cost structure in a rising rate environment. It moves from the current ~2% to a more robust 7.5%, utilizing the capacity efficiently.

<answer>7.5%</answer>