What an Electronic Logging Device Records, and What It Does Not
An ELD is an hours-of-service record, not a black box. Knowing the difference saves investigators from asking it questions it was never built to answer.
Since December 18, 2017, most interstate truck drivers have recorded their hours of service on an electronic logging device. Carriers that had already installed older automatic onboard recording devices had until December 16, 2019 to switch1. The ELD is often the first record requested after a serious crash. It answers some questions very well and others not at all.
What it records
An ELD connects to the truck’s engine and records a fixed set of data elements: date, time, the vehicle’s location, engine hours, vehicle miles, and identification for the driver, the vehicle and the motor carrier1. It records them at every change of duty status, at engine power-up and shutdown, and at least once an hour while the truck is moving. Logins, logouts and device malfunctions are time-stamped as well.
Driving time is automatic. When the truck’s speed passes a threshold that cannot be set higher than 5 miles per hour, the device switches the driver’s status to driving1. The other statuses (off duty, sleeper berth, on duty not driving) are entered by the driver.
Location is deliberately coarse. During on-duty driving, the recorded position is accurate to about a 1-mile radius. During authorized personal use of the truck it drops to about a 10-mile radius12.
The device also keeps a separate “Unidentified Driver” account. If the truck moves with no one logged in, the driving goes there. Drivers and carriers must review it and either assign the time to a driver or annotate why it is unassigned. Carriers keep those records for at least 6 months1.
What it does not record
An ELD is not a speed recorder or a crash recorder. FMCSA says plainly that ELDs “are not required to collect data on vehicle speed,” and that the ELD rule does not require real-time tracking2. The device uses speed only to decide whether the truck is moving. It does not log the speed curve, brake application, throttle position or a hard-braking event.
That data lives elsewhere: in the engine control module and in any telematics or camera systems the carrier runs, each with its own retention behavior. Our explainer on what a truck’s engine control module stores covers them. Many carriers buy ELD and telematics functions from one vendor on shared hardware, so a request for “the ELD data” alone may miss what the rest of the system holds.
Nor can the ELD say whether a driver slept. It shows when the driver was logged off duty or in the sleeper berth, not what happened then.
Edits and annotations
Drivers can edit their logs, within limits. Every change or addition must carry an annotation. A carrier may propose edits, but the driver must accept or reject them and recertify the record, and carriers may not coerce a false certification1.
Two limits matter most after a crash. Automatically recorded driving time cannot be shortened by edit. And the original records survive. FMCSA’s guidance says “the original ELD records are retained even when allowed edits and annotations are made”2, and the regulation bars carriers from altering or erasing the original data1. The edit history, showing what was changed, when and at whose request, is often as informative as the final log.
Personal conveyance and yard moves
A carrier may configure the ELD to let a driver flag two special driving categories: authorized personal use and yard moves. The driver selects the category before the movement and clears it after1.
Personal conveyance is driving a truck for personal reasons while off duty. FMCSA’s 2018 guidance allows it to be logged off duty only when the driver has been relieved from work and all responsibility for performing work by the carrier. The truck may be loaded, since the load is not being moved for the carrier’s commercial benefit at that time3. Driving to a nearby, reasonable, safe place to rest after loading or unloading can qualify. Driving to the carrier’s terminal after a delivery does not3. Because personal conveyance does not count as driving time, it is a recurring point of dispute when a crash happens during it.
Retention and supporting documents
Carriers must keep ELD records and supporting documents for 6 months, and keep a backup copy on a separate device12. Supporting documents are the business records used to check the log: bills of lading or other trip documents, dispatch records, expense receipts, fleet management messages, and payroll or settlement records. A carrier need not keep more than eight per driver per day, but must keep those with the earliest and latest times1.
Drivers must keep the current day and the previous 7 days available for inspection while on duty1.
How the records are requested
At roadside, the driver transfers the data to the inspector. Devices must support one of two transfer methods: telematics (wireless web services and email) or local transfer (USB and Bluetooth)2. The output follows a standard file format set in the regulation’s technical appendix1.
After a crash, the carrier holds the records and must produce them electronically when an authorized safety official asks1. In civil litigation they are sought through preservation letters and discovery, under rules that vary by court and state. The 6-month retention period is the practical clock: a request that arrives later may find only what the carrier chose to keep. Our guide to evidence after a truck crash covers how ELD data fits with the other records, and our hours-of-service explainer covers the limits the log is measured against.
