DIRT Report

Three-Year Trending: Statistical Analysis Confirms Upward Damage Trajectory

Looking at trends in damage and 811 center data can provide additional context beyond focusing on submissions for any individual year. CGA engaged a statistical consultant to analyze DIRT data from 2020-2022 and assess damage count trends.

Damage Trend Analysis Highlights:

• Damages per million dollars of construction spending and damages per one thousand 811 center transmissions increased 12.35% and 9.34% respectively from 2021 to 2022.
• Statistical regression analysis, controlling for other influencing factors like economic activity and population density, confirms an upward damage trend over the three-year period (2020-2022).
• Increased construction spending consistently correlates with more damages. If significant changes are not made to U.S. damage prevention, infrastructure funding will further strain the system, resulting in more damages in the coming years.

Methodology: Comparable Dataset

The trend analysis uses a comparable three-year dataset (2020-2022) of consistent DIRT contributors that includes a representative sample and typical distribution of reporting stakeholders in a given year (facility owners/operators, 811 centers, locators, excavators, public works and private water, and regulatory agencies). This approach provides a focused view of damage trends. The comparable dataset is also used to examine damage root causes in the next section of this Report.

Damage Trends and Construction Spending

In addition to analysis of the three-year comparable damage dataset, CGA’s statistical consultant incorporated 811 center data and construction spending into the analysis to evaluate how damage counts have changed in recent years.

As noted in the 2021 DIRT Report, CGA makes every effort to normalize variables that can complicate interpreting damage trends over time. For example, disproportionate inflation rates between sectors require closely examining construction spending. As in 2020 and 2021, construction spending figures were adjusted to the latest year’s (i.e., 2022 in this case) consistent dollars using a construction-specific price index to account for inflationary pressures. 

Regression Analysis

The damages per construction spending and per transmission metrics normalize the number of damages accounting for factors most directly linked to levels of excavation activity. However, there are other less direct factors that can also influence the number of damages, such as weather, population and the density of infrastructure in an area. To fully understand the damage trends, CGA's statistical consultant performed regression analysis on three years of comparable data at the state and national level, incorporating such additional variables. This more advanced analysis controls for other potential influences on the damage rate. (Visit Appendix B for regression methodology.)

National-level regression used building permits to indicate construction activity. State-level regression explored spatial variation and revealed influential predictors:

• Real GDP as an indicator of economic activity
• Housing starts indicating construction volume
• Population density capturing infrastructure density

The regression analysis tested whether damage trend results were statistically different over time. The analysis took into consideration the factors outlined above and suggests that the increase in damages per spending and transmission is partially explained by other variables. However, evidence shows 2022 damages were higher than 2021, pointing to a continued rise in damages.

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