To estimate S&P's credit trend for VINCI from 2021 to 2022, we follow the S&P general corporate methodology alongside considerations for the Transportation Infrastructure industry, as VINCI operates largely in concessions and contracting.

**Step 1: Identify the relevant industry**
VINCI operates extensively in toll roads, airports, and construction. We will apply the standard Corporate / Transportation Infrastructure principles for estimating Adjusted EBITDA, FFO, and Adjusted Debt.

**Step 2: Estimate the 2021 Adjusted EBITDA**
* Operating Profit (Reported): €4,438m
* Add back D&A: €3,219m
* Impairments/Provisions & Non-recurring adjustments: €206m (Impairments) + €26m (Non-recurring expenses)
* **2021 Adjusted EBITDA:** 4,438 + 3,219 + 206 + 26 = **€7,889m**

**Step 3: Estimate the 2021 FFO**
* Cash Interest Paid (Net): €557m
* Cash Taxes Paid: €1,213m
* **2021 FFO:** 7,889 - 557 - 1,213 = **€6,119m**

**Step 4: Estimate the 2021 Adjusted Debt**
* Reported Borrowings (Current & Non-current): €22,212m + €2,757m + €5,769m = €30,738m
* Add Leases (Current & Non-current): €524m + €1,574m = €2,098m
* Add Post-retirement/Pension Liabilities: €1,459m
* Less Eligible Cash & Cash Management Assets: €11,065m + €200m = €11,265m
* **2021 Adjusted Debt:** 30,738 + 2,098 + 1,459 - 11,265 = **€23,030m**

**Step 5: Calculate the 2021 Leverage Ratio**
* **2021 Adjusted Debt / Adjusted EBITDA:** 23,030 / 7,889 = **2.92x**

**Step 6: Calculate the 2021 FFO to Debt Ratio**
* **2021 FFO / Adjusted Debt:** 6,119 / 23,030 = **26.6%** (or 0.266)

**Step 7: Estimate the 2022 Adjusted EBITDA**
* Operating Profit (Reported): €6,489m
* Add back D&A: €3,613m
* Impairments & Non-recurring adjustments: €0m (Impairments) - €8m (Non-recurring gains)
* **2022 Adjusted EBITDA:** 6,489 + 3,613 - 8 = **€10,094m**

**Step 8: Estimate the 2022 FFO**
* Cash Interest Paid (Net): €563m
* Cash Taxes Paid: €1,603m
* **2022 FFO:** 10,094 - 563 - 1,603 = **€7,928m**

**Step 9: Estimate the 2022 Adjusted Debt**
* Reported Borrowings: €20,425m + €3,205m + €6,368m = €29,998m
* Add Leases: €522m + €1,580m = €2,102m
* Add Post-retirement/Pension Liabilities: €1,149m
* Less Eligible Cash & Cash Management Assets: €12,578m + €755m = €13,333m
* **2022 Adjusted Debt:** 29,998 + 2,102 + 1,149 - 13,333 = **€19,916m**

**Step 10: Calculate the 2022 Leverage Ratio**
* **2022 Adjusted Debt / Adjusted EBITDA:** 19,916 / 10,094 = **1.97x**

**Step 11: Calculate the 2022 FFO to Debt Ratio**
* **2022 FFO / Adjusted Debt:** 7,928 / 19,916 = **39.8%** (or 0.398)

**Step 12: Classify the Year-on-Year Credit Trend**
* **Signal 1 (Leverage):** 1.97x - 2.92x = **-0.95x**. This is well past the -0.2x threshold required for an "Improving" trend. 
* **Signal 2 (Cash-Flow Coverage):** 39.8% - 26.6% = **+13.2 percentage points** (+0.132). This is robustly above the +0.03 threshold required for an "Improving" trend.

Both signals perfectly align, supported by surging profitability parameters, strong operating cash generation post-pandemic, and net debt reduction. 

<answer>Improving</answer>