Tunnel Driving Procedures for Commercial Vehicles: Safety and Compliance

Tunnel Restrictions for Commercial Vehicles

Many tunnels restrict or prohibit hazardous materials, oversized vehicles, and vehicles carrying certain cargo types. These restrictions exist because a fire or hazmat release inside a tunnel is exponentially more dangerous than one on an open road due to the enclosed space, limited ventilation, and restricted escape options.

Hazmat tunnel restrictions vary by tunnel. Some tunnels prohibit all hazmat. Others allow certain classes while restricting others. Some restrict hazmat to specific hours or require escorts. The FHWA assigns tunnel restriction codes (A through E) based on the types of hazmat allowed. Check the specific restrictions for every tunnel on your route before departure, not when you are approaching the tunnel entrance.

Height and weight restrictions are common for tunnels. Older tunnels may have clearances as low as 12 to 13 feet, well below the 13 feet 6 inches standard height of a dry van trailer. Weight restrictions exist because the tunnel structure has load-bearing limits. Overweight vehicles stress the tunnel's structural support and road surface.

Some tunnels require headlights on, windows closed, and radios off. These requirements ensure visibility, prevent exhaust accumulation inside the cab, and avoid electronic ignition sources near potential fuel vapors. Follow all posted requirements at each tunnel entrance.

Speed and Safety Inside Tunnels

Tunnel speed limits are typically lower than the approach highway speed, usually 35 to 55 mph depending on the tunnel length, width, and design. Reduce to the tunnel speed before entering because braking inside the tunnel is more hazardous than on open road due to the confined space and inability to swerve or leave the road.

Maintain your lane precisely inside the tunnel. Tunnel lanes are often narrower than highway lanes, and the walls and barriers are unforgiving if you drift. The visual effect of the tunnel walls and lighting can create an illusion of narrowing that causes some drivers to unconsciously slow down or drift from their lane.

Maintain adequate following distance inside the tunnel. In the event of a sudden stop ahead, you have no shoulder or escape route in a tunnel. Following distance of 7 or more seconds gives you maximum stopping room. If traffic slows or stops inside the tunnel, use your hazard flashers to alert following vehicles.

Never pass another vehicle inside a tunnel unless the tunnel has designated passing lanes with adequate width. The confined space, limited visibility, and absence of shoulders make passing inside tunnels extremely dangerous.

Ventilation and Air Quality Awareness

Tunnel ventilation systems manage the air quality inside the tunnel by removing exhaust fumes and providing fresh air. Long tunnels (over 1,000 feet) typically have mechanical ventilation fans that draw in fresh air and exhaust contaminated air. However, during heavy traffic, especially in tunnels with stop-and-go conditions, carbon monoxide and particulate levels can rise significantly.

Keep your windows closed and your ventilation system on recirculate when driving through tunnels. This prevents drawing in tunnel air, which has higher concentrations of diesel exhaust and carbon monoxide than outside air. If you are stuck in a tunnel with the engine running for an extended period, monitor for symptoms of CO exposure: headache, dizziness, and nausea.

In the event of a fire in a tunnel, the ventilation system may reverse to push smoke in one direction, creating a clear zone for evacuation. Follow the tunnel's emergency signage, which indicates evacuation routes, fire extinguisher locations, and emergency exits. Understanding the tunnel's ventilation response helps you make the right decision about whether to drive through smoke or stop and evacuate.

Some long tunnels have emergency ventilation buildings at intervals along the route. These enclosed areas provide refuge with clean air during a fire or hazmat event. Know the locations of these refuges in tunnels you drive through regularly.

Emergency Response Inside Tunnels

If your vehicle breaks down inside a tunnel, pull as far to the right as possible, turn on hazard flashers, and immediately call the tunnel's emergency number (posted at tunnel entrances and intervals inside the tunnel). Do not attempt to make repairs inside the tunnel because the confined space, limited visibility, and proximity to traffic make roadside repairs extremely dangerous.

If a fire occurs inside the tunnel, your response depends on the fire's location relative to your position. If the fire is ahead of you and you can back up safely, do so. If the fire is behind you and you can drive through to the exit, do so quickly. If you are trapped between the fire and other vehicles, turn off the engine, leave the vehicle, and proceed to the nearest emergency exit on foot. Do not stay in the vehicle hoping the fire will be extinguished.

Tunnel fires produce toxic smoke that rises and fills the tunnel ceiling first, then descends. Stay low if you must walk through smoke. Follow the emergency exit signs and tunnel lighting that indicates the evacuation direction. Some tunnels have emergency walkways and cross-passages that provide safe evacuation routes.

If you are involved in or witness an accident inside a tunnel, call emergency services immediately using the tunnel's emergency phone or your cell phone (if service is available, which it may not be in all tunnels). Turn off your engine to reduce emissions in the enclosed space. Set emergency triangles if possible to warn approaching traffic. Help injured persons if you can do so safely, and be prepared to evacuate if fire develops.

Planning Routes Through Major US Tunnels

The Lincoln Tunnel and Holland Tunnel (New York/New Jersey) are among the busiest truck tunnels in the US. Both have hazmat restrictions, height limits, and peak-hour commercial vehicle restrictions. The Holland Tunnel prohibits all commercial vehicles between certain hours. Plan alternate routes (George Washington Bridge, Goethals Bridge) during restriction periods.

The Chesapeake Bay Bridge-Tunnel (Virginia) includes two tunnels that restrict certain oversized vehicles and hazmat loads. High-wind closures are common due to the bridge's exposed location. Monitor wind advisories before crossing.

The Eisenhower Tunnel (Interstate 70, Colorado) at 11,158 feet elevation has specific hazmat restrictions and is the highest point on the Interstate highway system. Winter conditions can close the tunnel approaches, and chain requirements are common.

The Ted Williams Tunnel and Sumner Tunnel (Boston) have hazmat restrictions and tolls. The Big Dig tunnel system connects to these tunnels and has its own set of restrictions and regulations for commercial vehicles.

Research every tunnel on your planned route before departure. The FHWA maintains a database of tunnel restrictions that is accessible online. Commercial GPS systems include tunnel restriction data, but verify against official sources because GPS databases may not reflect the most recent changes.