What is an electronic logging device (ELD) primarily used for?

An electronic logging device (ELD) is primarily used to automatically record driving time, which is essential for complying with hours of service regulations set forth by transportation authorities. ELDs are designed to connect to a vehicle's engine and monitor driving hours, thereby promoting safety on the roads by preventing driver fatigue. This automatic recording helps provide an accurate account of a driver's work hours, ensuring that they do not exceed legal limits and thereby enhancing overall road safety and regulatory compliance.

The other options, while related to vehicle operation, do not accurately define the primary function of an ELD. Tracking vehicle mileage, monitoring fuel consumption, and assisting with route planning are functions typically handled by different systems or devices, such as odometers, telematics systems, and GPS navigation tools. Thus, while these functions are important in their own right, they are not the main purpose of an ELD.