To determine the appropriate level of hybrid bond issuance for Ferrovial SA, we analyze its financial position, credit metrics, and the strategic rationale for hybrids based on the provided guidelines.

**1. Current Financial Profile and Leverage:**
As of December 31, 2022, Ferrovial reports:
- Total Equity: €6,354 million
- Total Financial Debt: €11,653 million (Calculated as Noncurrent borrowings of €10,776m + Current borrowings of €877m)
- Adjusted Debt / Total Adjusted Capital (Debt / (Debt + Equity)): 64.7%
This leverage ratio is elevated, pushing the boundaries for a solid investment-grade profile, particularly for an infrastructure entity that typically targets lower leverage. 

**2. Outstanding Hybrids:**
Ferrovial already has hybrid bonds in its capital structure. The "Other Equity Securities" line item, which includes these hybrids, stands at €508 million. At a 50% equity credit basis, this implies an outstanding hybrid nominal of ~€1,016 million. This represents approximately 6.6% of their total adjusted capital, meaning they already utilize hybrids to optimize leverage. 

**3. Rationale for Additional Issuance:**
Ferrovial is an infrastructure and construction group with significant investments in infrastructure projects (€13.66 billion in intangible/assets). The industry naturally requires heavy capital expenditure (capex) and concession funding. Additionally, the company is undergoing a transformational relocation of its parent company to the Netherlands (as indicated by the corporate identity note), which involves strategic restructuring and potential capex/acquisition pipelines. The year 2022 also saw a dramatic shift in the interest rate environment, with the 5Y swap curve moving from deeply negative to +1.72%, which materially increases refinancing costs and the cost of new debt. 

Given the high leverage (64.7%), there is "significant leverage pressure" and "rating headroom moderately constrained." Issuing hybrids up to 11.25% of total adjusted capital would provide a meaningful cushion to stabilize the adjusted leverage trajectory and preserve the investment-grade rating against macroeconomic and operational volatility. The guidelines note that 11.25% is appropriate when there is high capex intensity or large acquisition pipelines, and the preservation of IG status strongly depends on capital structure optimization.

**4. Hybrid Limits:**
S&P limits equity credit from hybrids to a maximum of 15% of total adjusted capital. Ferrovial currently sits at ~6.6%. An issuance moving them toward the 11.25% threshold would fall well within S&P's limits and the €3 billion annual issuance cap, providing necessary balance sheet resiliency without aggressively maxing out the equity credit basket. 

**Conclusion:**
Given the high underlying leverage, the capital-intensive nature of the business, and the need to preserve an investment-grade rating amid rising interest rates and strategic corporate changes, a hybrid issuance targeting 11.25% of total adjusted capital is highly advisable.

<answer>11.25%</answer>