Detention
Detention compensates a carrier for equipment or time held beyond the free period outside the terminal: a container or chassis kept too long after gating out, or a truck driver stuck at a dock past the allowed loading window. It is the mirror image of demurrage, which accrues while a container is still inside the terminal. Equipment detention bills per day; driver detention bills per hour.
Examples
Driver detention: A receiving dock with two free hours runs a chronic backlog, and trucks average 3.7 hours door to door. At $75 per detention hour across 30 inbound loads a week, the site pays about $3,800 a week, nearly $200,000 a year, for slow unloading.
Container per diem: An importer strips containers only when warehouse space opens up, so empties return an average of six days past free time at $125 per day. Across 40 containers a month, that habit costs $30,000 monthly until the team sets a 48-hour strip-and-return rule.
Definition
Where the equipment sits decides which charge applies. A late container inside the terminal accrues demurrage; the same container kept too long after it gates out accrues detention, which ocean carriers often call per diem. Trucking applies the same logic to people: hold a driver at your dock beyond the free window, typically the first one or two hours, and the carrier bills detention by the hour.
Carriers charge it because the equipment is their working capital. A container parked behind a consignee's warehouse cannot be repositioned for the next booking, and a driver stuck at a dock cannot take the next load, so detention is priced to change behavior, not just to recover cost. On freight invoices it lands among the accessorial charges, where at many shippers it is the largest single line.
The fix is operational rather than contractual: measure dock dwell time by door and by shift, schedule unloads against real labor capacity, strip and return ocean containers on a standing cadence, and stop treating carrier equipment as free warehouse space. Facilities that turn trailers in under two hours rarely see the charge at all.
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