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The article highlights several limitations of using Bluetooth traffic data for travel time prediction, including:1. Computational efforts: Processing Bluetooth data requires significant computational resources, especially when path information is needed.2. Spatial coverage: While Bluetooth devices can extend spatial coverage at a low cost, the range of Bluetooth technology has limitations, restricting the area for collecting traffic data.3. Accuracy and reliability: Various factors like signal interference, device malfunctions, and limited penetration rates can affect the accuracy and reliability of Bluetooth data.4. Limited information: Bluetooth data primarily provides information about the travel time between two specific points or detectors, which may not capture the complete picture of traffic conditions.5. Data filtering and cleaning: Bluetooth data often requires filtering and cleaning processes to remove outliers, errors, and inconsistencies, which can be time-consuming.6. Integration with other data sources: To enhance the accuracy of travel time predictions, Bluetooth data needs to be integrated with other data sources like GPS, video data, or weather information, but integrating multiple data sources can be complex.In summary, while Bluetooth traffic data offers advantages such as low cost and high-sampling rates, it also has limitations that need to be considered when using it for travel time prediction.