Investigating the contributors to hit-and-run crashes using gradient boosting decision trees

This paper uses the 2021 traffic crash data from the NHTSA CRSS as a sample for model training and validation. The CRSS data collects crash report data provided by police departments from all 50 states in the United States. It details various factors of each traffic crash, including crash information, driver information, vehicle information, road information, and environmental information.The crash accident data provided by CRSS include crash-related details such as the location, time, cause, type of crash, driver’s age, gender, attention level, injury status, risky driving behavior, vehicle type, usage, damage, and hit-and-run situations. However, due to the separate recording of the dataset and the presence of systematic errors and redundant information, the CRSS 2021 data undergo the following merging and filtering processes:1) Match and merge separately recorded data based on the unique case number "CASENUM" in the dataset.2) Records with missing values in critical variables (e.g., whether the crash involved a hit-and-run) were removed to avoid bias in the analysis. For non-critical variables, missing values were imputed using the mean or mode depending on the variable type. For continuous variables, such as speed limits, we used mean imputation. For categorical variables (e.g., weather, road surface conditions), mode imputation was applied.3) Noise in the dataset arises from both human error in crash reporting and random fluctuations in recorded variables. We used z-scores to detect and remove extreme outliers in numerical variables (e.g., speed limits, crash angle). Data points with a z-score beyond ±3 standard deviations were considered outliers and were excluded from the analysis. To handle noisy fluctuations in continuous variables (e.g., speed limits), we applied a symmetrical exponential moving average (EMA) filter.After processing, the CRSS 2021 data include a total of 54,187 crash accidents, among which there are 5,944 hit-and-run accidents, accounting for 10.97% of crash accidents. The hit-and-run and non-hit-and-run categories face a serious class imbalance issue, and data balancing processing is applied to the target variable during parameter calibration. Hit-and-run crashes constitute a relatively small proportion of total crashes in the dataset, leading to class imbalance in the binary classification target. To address this issue, we utilized the resampling techniques available in the data mining software. Specifically, random undersampling was applied to the majority class (non-hit-and-run crashes), while Synthetic Minority Over-sampling Technique (SMOTE) was used for the minority class. This ensured balanced class distribution in the training set, improving model performance and preventing the classifier from being biased toward the majority class.