What are ADR tunnel restriction categories and which European routes are affected?

ADR assigns road tunnels to one of five categories — A through E — governing which dangerous goods may pass through. Category A imposes no restrictions. Categories B through E progressively restrict higher-risk classes and quantities, with Category E excluding most dangerous goods except limited and excepted quantities. National road authorities assign categories to individual tunnels. Alpine freight corridors — the Brenner Pass, Mont Blanc, Gotthard, and Fréjus tunnels — each carry category restrictions that vary by UN number. Carriers must confirm the applicable tunnel category for their specific goods before departure — the tunnel category is a pre-booking compliance check, not a post-transit formality.