Electronic Logging Devices: What ELD Data Actually Records

More than eight years after the Federal Motor Carrier Safety Administration's (FMCSA) electronic logging device (ELD) mandate took full effect in December 2017, basic misconceptions about what these devices record persist — among drivers, among carriers, and notably among reporters covering the trucking industry. The rule is narrower than the popular picture of an always-on tracking computer. It is also more specific. Understanding the actual data set matters, because the same recorded fields show up later in roadside inspections, audits, civil litigation, and the post-incident investigations covered in our piece on telematics in accident reconstruction.

The regulatory baseline

The ELD rule lives in 49 CFR Part 395, Subpart B. It applies to most commercial motor vehicle drivers who are required to keep records of duty status (RODS). The rule prescribes a list of data elements the device must capture automatically, the intervals at which they must be captured, and the formats in which they must be transmitted to an authorized safety official. Anything outside that list is at the carrier's discretion — and many of the additional fields fleets collect come from telematics layered on top of the ELD, not from the ELD itself.

What the device captures automatically

An ELD is required to be integrally synchronized with the vehicle's engine. The synchronization is what distinguishes it from the older Automatic On-Board Recording Device (AOBRD) standard and from paper logs. When the engine starts, the device must record the event. When the vehicle begins moving — defined in the rule as reaching a speed threshold of five miles per hour — the device must automatically place the driver in driving status. When the vehicle has been stationary for five consecutive minutes, the device prompts the driver to confirm whether the duty status should change.

Beyond those triggered events, the ELD captures position data at 60-minute intervals during driving and at every duty-status change, power-on, power-off, and yard-move or personal-use transition. The position is recorded with the limited accuracy described above; it is not a continuous GPS track of the route. This is one of the most consistently misunderstood points: a compliant ELD does not, by regulation, log a breadcrumb trail of where the truck went between hourly samples. Carriers that want that level of detail rely on a separate telematics layer.

What an ELD does not record

The rule says nothing about audio. It says nothing about video. It does not require continuous GPS tracking, biometric data, in-cab imagery, or any record of the driver's communications. It does not require the device to record engine fault codes, brake applications, lane departures, or driver-monitoring events. All of those data streams exist in modern trucks, but they exist because of telematics, dashcams, and engine control module (ECM) features that operate independently of the ELD requirement.

This separation matters for legal and privacy questions. When a driver is told that "the ELD captured" a particular event, the more accurate statement is often that the carrier's integrated telematics platform — which happens to include ELD functionality — captured it. The distinction is not academic. The required ELD data set is narrowly defined and tightly regulated; the optional telematics data set is broad, vendor-specific, and governed mostly by carrier policy and state privacy law. We covered the privacy side of that gap in our article on continuous monitoring.

How the data leaves the device

The ELD must be capable of producing the required record set in a standardized output format for an authorized safety official. The two primary methods specified in the rule are a telematic transfer (web service plus email) and a local transfer (USB 2.0 plus Bluetooth). The output file format is a comma-delimited file conforming to the FMCSA's published data dictionary. In practice, during roadside inspections, an officer typically requests an electronic transfer to the eRODS (Electronic Records of Duty Status) system; if transfer fails, the driver presents the display on the device or a printout.

The required ELD data set is narrowly defined. The optional telematics data set sitting beside it is not.

Retention

Carriers must retain RODS and supporting documents for six months. Supporting documents are defined in 49 CFR § 395.11 and include items like bills of lading, fuel receipts, and dispatch records that can corroborate the duty status reflected in the ELD. The ELD itself must retain on-device data for the current 24-hour period plus the previous seven consecutive days; the back-office record-keeping requirement extends that to six months. After a reportable accident, preservation duties expand substantially — see what happens to truck data after a crash for the post-incident pipeline.

Edits, annotations, and the audit trail

One of the most important features of the ELD standard is that the device must retain an immutable record of original entries and any subsequent edits. A driver may annotate a record to correct a missed status change; a carrier's safety office may request an edit, which the driver must confirm. The device retains the original entry, the edit, the annotation, and the identity of the person who made each change. In audits and investigations, that edit history is often where the substantive findings come from — not from the duty status numbers themselves but from the pattern of changes around them.

The practical takeaway

For fleet operators, the ELD is the regulated floor, not the ceiling, of recorded data. For drivers, it is worth knowing exactly what the federally mandated device records — and recognizing that almost everything else carriers collect (dashcam footage, harsh-braking events, dwell time, route deviation) comes from a separate layer governed by carrier policy. The distinction shapes everything from a roadside inspection to a deposition years later.