What the 2025 IMDG Code Changes for RoRo

IMDG Code Amendment 42-24 became mandatory on 1 January 2026, and for vehicle-carrier operators the concrete change is a reclassification: electric vehicles now have their own UN numbers instead of the generic catch-all. The headline is UN 3556 — lithium-ion-battery-powered vehicles — replacing UN 3171 for EVs. It does not make every EV a placarded dangerous-goods unit on a PCTC, but it does change how the deck is described, declared and, ultimately, known.

The headline: EVs get their own UN numbers

Amendment 42-24 splits battery-powered vehicles out of one generic entry into chemistry-specific ones. UN 3556 covers lithium-ion-battery-powered vehicles, UN 3557 lithium-metal-battery-powered vehicles, and UN 3558 sodium-ion-battery-powered vehicles. The old entry, UN 3171, is now restricted to vehicles powered by wet batteries, metallic sodium batteries or sodium-alloy batteries — it can no longer be used for a lithium-ion car. The amendment was available voluntarily from 1 January 2025, the dual-use transition ended on 31 December 2025, and it has been mandatory since 1 January 2026. The practical effect is a data one: a shipper's declaration and the vessel's dangerous-goods manifest can now distinguish a lithium-ion vehicle from a wet-cell one by UN number, a signal that simply did not exist while everything travelled as UN 3171.

What still exempts EVs on a RoRo deck

The reclassification did not, by itself, make EVs placarded dangerous goods on a car carrier. Vehicles driven aboard a designated ro-ro ship remain outside most IMDG documentation, marking and placarding requirements provided the long-standing carriage conditions hold: no electrolyte or battery leakage, the installed battery protected against short circuit and accidental activation, and the unit neither damaged nor defective. Amendment 42-24 keeps that architecture and clarifies it at the edges — for example, its Special Provision 388 confirms that hybrid vehicles carried on container ships follow the same regime as SP 961.1 on ro-ro decks, and sodium-ion vehicles under UN 3558 gain their own conditional relief. So a sound, correctly declared EV is still not a placarded package at the ramp; the exemption simply now hangs on a more precisely defined vehicle class.

Where the exemption stops: damaged, defective, used

The exemption is conditional, and the conditions bite hardest where the cargo is least known. A damaged, defective or recalled lithium battery falls outside the vehicle exemption and into the stricter special-provision regime — regardless of state of charge — because the carriage relief assumes an intact, non-hazardous unit. For the fast-growing used-EV export trade, where a vehicle's battery history and state of health are often opaque, that turns pre-shipment verification from a paperwork exercise into something closer to a fitness-for-purpose check. The operator absorbs most of the documentation burden by tightening the loading manual; the harder problem is establishing the true carrying condition of a second-hand battery before it is lashed to a deck. [VERIFY: the degree to which individual flag states and terminals have standardised used-EV pre-shipment battery inspection is an evolving operational picture, not a single published rule.]

What it means for vehicle-carrier operators

The practical burden of the 2026 change is data, not placards. Two things follow for operators. First, the shipper's declaration and the stowage plan must carry the correct chemistry-specific UN number, so booking systems, loading manuals and dangerous-goods manifests need updating away from a blanket UN 3171 habit. Second, and more useful, the manifest now encodes what a deck actually holds — how many lithium-ion vehicles, and where — which is exactly the input that stowage segregation, boundary planning and per-deck fire-risk profiling depend on. Classification is not detection, and a correct UN number does not prove a battery is sound. But a deck described precisely is a deck that can be planned for, and that is the quiet value of the 42-24 reclassification for the vehicle-carrier trade.

Sources

• IMO — International Maritime Dangerous Goods (IMDG) Code, Amendment 42-24: mandatory from 1 January 2026 (available voluntarily from 1 January 2025, transition ending 31 December 2025). New entries UN 3556 (lithium-ion-battery-powered vehicles), UN 3557 (lithium-metal-battery-powered vehicles) and UN 3558 (sodium-ion-battery-powered vehicles); UN 3171 restricted to wet-battery, sodium-metal and sodium-alloy vehicles — imo.org.
• ICHCA International — 'IMDG Code Amendment 42-24: summary of main changes': the UN 3556/3557/3558 split, the UN 3171 restriction, Special Provision 388 (hybrid vehicles on container ships aligned with SP 961.1 on ro-ro decks) and the sodium-ion conditional exemption.
• Maersk / Britannia P&I / CIRS — carrier and insurer guidance on Amendment 42-24: booking and declaration changes for battery-powered vehicles, the end of the concurrent UN 3171 / UN 3556 transition on 31 December 2025, and the tightened conditions for the vehicle carriage exemption.
• IMDG Code special provisions for vehicles on ro-ro ships (SP 961 / SP 962): conditional relief from marking, labelling, placarding and documentation for vehicles on a designated ro-ro ship where there is no leakage, the battery is protected against short circuit and accidental activation, and the unit is not damaged or defective.