ADR defines five tunnel categories with progressively tighter restrictions on dangerous goods transport.
- Category A — no restriction.
- Category B — passage forbidden for goods causing a very large explosion.
- Category C — forbidden for goods causing a very large explosion, a large explosion, or a large toxic release.
- Category D — restriction for goods which may lead to a very large explosion, a large explosion, a large toxic release or a large fire.
- Category E — restriction on the carriage of all dangerous goods other than those marked
(-)in Column 15 of Table A, and on all dangerous goods carried under Chapter 3.4 (limited quantities) where the quantities exceed 8 tonnes total gross mass per transport unit (1.9.5.2.2).
The definitions come from 1.9.5.2.2, and the actual per-load restrictions from the table in 8.6.4 — which also carries the two quantity-dependent codes B1000C (net explosive mass above/below 1 000 kg) and C5000D (above/below 5 000 kg).
Each substance carries a tunnel restriction code in Column 15 of ADR Table A (formats like (B/D), (C/E), (D)). Per ADR 8.6.4, in a compound code X/Y the first letter X governs tank carriage (for code D/E — bulk or tank carriage), and the second letter Y governs other carriage, such as packages. Code (-) means no tunnel restriction (8.6.3.1), and goods carried under 1.1.3 are not subject to the restrictions unless the transport unit has to be marked under 3.4.13 (8.6.3.3).
References — ADR 2025 1.9.5.2.2 (tunnel categories), 8.6.3 (tunnel restriction codes), 8.6.4 (restrictions per code).