## 4 Results
### Descriptive Statistics
#### 4.1.4 Performance  
Figure 5 shows the performance of the bridge deck across all bridge-wearing surfaces. The performance of the bridge deck seems to vary significantly with various bridge-wearing surfaces, as reflected by the Baseline Difference Score (BDS). The normality test (Shapiro-Wilk test) suggests that the distribution of performance (BDS) score is not normal, with a \(p\)-value (0.0) less than 0.5. The Kruskal-Wallis (non-parametric) test reveals that minor differences in performance scores between bridge decks with different wearing  
Figure 4: Distribution of maintenance interventions (categorized as zero, one, and two) across various bridge wearing surface types.  
Figure 3: Distribution of computed Deterioration Scores (based on computation of slope) across different types of bridge wearing surfaces: Monolithic Concrete, Gravel, Wood or Timber, Bituminous, Low Slump Concrete, and Other.  
surfaces, while relatively small, are statistically significant. It is essential to note that the BDS indicates the long-term performance of bridge components, considering the average condition rating of bridge decks with specific surface types with respect to their age.  
The positive BDS values indicate that certain types of bridge decks with wearing surfaces perform better than the average, with Monolithic Concrete (0.16) and Low Slump Concrete (0.37) demonstrating the highest median baseline difference scores. These high BDS values signify a superior than average performance of bridges with these surface types, possibly due to their durable and resilient nature.  
Conversely, the negative BDS values for Bituminous (\(-\)0.67) and Gravel (\(-\)0.29) deck-wearing surfaces suggest that these bridges perform below the average. These wearing surfaces may be more prone to damage and deterioration due to traffic load, environmental conditions, or maintenance practices. The Bituminous wearing surface shows a low BDS, indicating a much worse performance than the average bridge deck.  
The magnitude of the BDS reflects the extent to which a specific bridge-wearing surface's performance deviates from the baseline, as seen in Figure 6. Therefore, the larger the absolute value of the BDS, the more significant the difference from the average performance of the bridge deck. According to the BDS, this understanding allows for more targeted and effective bridge maintenance strategies, focusing on wearing surfaces that show a tendency to underperform. Conversely, it may also guide future bridge design choices toward materials that have demonstrated superior long-term performance.  
Figure 6 presents a comparison of the baselines--defined as the average condition rating relative to age--for all bridge decks in Nebraska, labeled as overall (Deck - Baseline), against individual wearing surface types: Monolithic Concrete, Gravel, Wood or Timber, Bituminous, Other, and Low Slump Concrete. It is important to remember that the overall category may encompass bridges not included in this specific study. When examining individual wearing surface types, bridges with decks composed of Monolithic Concrete and Low Slump Concrete exhibit superior performance compared to the overall deck baseline. This indicates that these surface types may have a better-than-average longevity relative to their age. In contrast, decks with Bituminous and Wood or Timber-wearing surfaces show the lowest performance relative to the deck-baseline. This suggests these bridge decks might not age well or be more susceptible to wear and tear or deterioration.  
Figure 5: Baseline Difference Score (BDS) across various types of bridge wearing surfaces: Monolithic Concrete, Gravel, Wood or Timber, Bituminous, Low Slump Concrete, and Other.