Based on the financial data and market context provided for FERROVIAL SA, the recommendation for the extent to which the entity should issue hybrid bonds in the next 18 months is 0%. 

Here is the detailed reasoning:
- **Historical Issuance & Current Capital Structure**: The provided data explicitly states that Ferrovial did not issue hybrid bonds in 2021 or 2022 and that its hybrid issuance has "stopped." The company currently has no material hybrid bonds in its capital structure (the adjustments for perpetual subordinated bonds in equity are negligible). As noted in the guidelines, the absence of recent hybrid bond issuance is a strong and reliable indicator that the firm has reasons to avoid this instrument moving forward.
- **Liquidity and Refinancing Needs**: The company finished the 2022 fiscal year with a massive liquidity buffer, holding over 5.1 billion EUR in cash and cash equivalents. With such a robust cash position compared to its current borrowings (877 million EUR), there are low immediate refinancing needs that would necessitate tapping into the more expensive hybrid bond market to preserve liquidity.
- **Cost of Debt**: Interest rates and swap curves climbed sharply in 2022 (e.g., the 5Y swap curve averaged 1.726%, up from negative territory in the prior two years, with the sub-senior delta expanding as well). Given the recent surge in yields and spreads for subordinated debt, issuing hybrid bonds now would materially increase the company's weighted average cost of capital without offering a commensurate strategic benefit. 
- **Leverage and Credit Profile**: Ferrovial generates strong operational cash flows (over 1 billion EUR in operating cash flows for 2022) and has a flexible, well-capitalized balance sheet. There is no evidence of a transformational M&A program, exorbitant capex pipeline, or severe leverage pressure that would threaten their investment-grade preservation and force a capital structure optimization via hybrids. 

For these reasons, the company does not need the equity credit provided by hybrid bonds and should avoid the higher interest costs associated with them.

<answer>0%</answer>