What Are Tunnel Restriction Codes?
ADR tunnel restriction codes determine whether a vehicle carrying dangerous goods is permitted to pass through a road tunnel. Tunnels present unique risks for dangerous goods incidents — confined space, limited ventilation, restricted evacuation routes, and the potential for catastrophic consequences from fires or toxic releases underground.
Every road tunnel that applies dangerous goods restrictions is assigned a tunnel category (A through E), and every dangerous goods entry in the ADR list has a corresponding tunnel restriction code that determines which tunnel categories it may or may not pass through.
You can see the tunnel restriction code for any UN number in the ADR dangerous goods lookup.
The Five Tunnel Categories
Tunnels are classified into five categories based on the level of restriction they impose. Category A is the least restrictive and Category E is the most restrictive:
Category A — No Restrictions
No restrictions on the transport of dangerous goods beyond the general ADR provisions. Most motorway tunnels and short tunnels fall into this category.
Category B — Restricted
Restricts dangerous goods that could lead to a very large explosion. Affected: Class 1 goods in large quantities, certain explosives precursors, and some self-reactive substances.
Category C — More Restricted
Restricts goods that could lead to a very large explosion, a large explosion, or a large toxic release. Includes all Category B restrictions plus certain toxic gases, flammable liquids in tanks, and toxic liquids.
Category D — Highly Restricted
Restricts goods that could lead to a very large explosion, a large explosion, a large toxic release, or a large fire. In addition to Category C restrictions, this includes most flammable liquids and flammable gases in significant quantities.
Category E — Most Restricted
Restricts all dangerous goods other than those carried under exemptions (e.g., 1.1.3.6 small quantities, limited quantities, or excepted quantities). Essentially, only fully exempt loads may pass through Category E tunnels.
How Tunnel Codes Appear in the ADR List
In Table A of the ADR dangerous goods list (Column 15), each entry has a tunnel restriction code. These codes use the format of the letter(s) of the tunnel categories where the goods are restricted, sometimes with additional qualifiers in parentheses:
- (B) — Passage prohibited through Category B, C, D, and E tunnels
- (B/D) — Prohibited through B, C, D, E tunnels when carried in tanks; prohibited through D, E tunnels in other cases
- (B/E) — Prohibited through B, C, D, E tunnels when carried in tanks; prohibited through E tunnels in other cases
- (C) — Prohibited through C, D, and E tunnels
- (C/D) — Prohibited through C, D, E tunnels when in tanks; prohibited through D, E tunnels otherwise
- (C/E) — Prohibited through C, D, E tunnels when in tanks; prohibited through E tunnels otherwise
- (D) — Prohibited through D and E tunnels
- (D/E) — Prohibited through D, E tunnels when in tanks; prohibited through E tunnels otherwise
- (E) — Prohibited through E tunnels only
- (—) — No tunnel restriction
The slash notation (e.g., B/D) indicates different restrictions depending on whether goods are in bulk/tank or in packages. The first letter applies to tank transport; the second to packaged goods.
UK-Specific Tunnel Restrictions
The UK has several major tunnels with dangerous goods restrictions. While the UK follows ADR tunnel categorisation, some tunnels have additional or specific rules:
- Dartford Crossing (Dartford Tunnel): Category E tunnel. Most dangerous goods loads must use the Queen Elizabeth II Bridge (eastbound). Westbound traffic through the tunnel has significant DG restrictions. Vehicles carrying dangerous goods must display appropriate orange plates and contact the tunnel operator.
- Channel Tunnel (Eurotunnel): Has its own comprehensive dangerous goods rules that go beyond standard ADR tunnel codes. A specific list of prohibited and restricted goods applies. Consignors must declare DG loads in advance, and certain classes (notably Class 1 and Class 7) are completely prohibited. Always check the current Eurotunnel dangerous goods policy before booking.
- Tyne Tunnel: Restrictions on dangerous goods transport, particularly for flammable liquids and gases. Category D applies to the older tunnel bore; check current restrictions for the new tunnel bore.
How to Check Tunnel Codes
Use the FreightUtils ADR lookup to search any UN number and see its tunnel restriction code displayed on the detail page. The tunnel code is shown alongside the transport category, hazard class, and packing group.
For mixed loads, you need to consider the tunnel codes for every item in the consignment. The most restrictive code applies to the whole vehicle. Use the ADR 1.1.3.6 calculator to check whether your load qualifies for the small quantity exemption that permits passage through more restrictive tunnels.
Practical Tips for Route Planning
- Always check tunnel codes before planning a route, not after loading
- If a tunnel restricts your load, plan an alternative surface route in advance
- Night-time or weekend restrictions may apply — some tunnels only restrict DG during peak hours
- Mixed loads take the most restrictive tunnel code of all goods on board
- Exempted loads (1.1.3.6, LQ, EQ) can generally pass through all tunnel categories, but check local rules
- Keep tunnel restriction codes visible in your transport documentation