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TunnelUnited States

An introduction to the traffic rules and road signs of United States. Learn about driving, road safety and much more in our illustrated book, with answers to frequently asked questions.

For informational purposes only. Always follow official regulations. Some content and images were created with AI assistance.

Traffic signs
Traffic rules
United States

9. Tunnel

A tunnel is a covered passage that carries a road through or beneath an obstacle such as a hill, mountain, building, waterway or another transport route. Road tunnels may contain one or more traffic lanes and can carry traffic in one or both directions.

Driving in a tunnel requires particular attention because visibility, available escape routes and space for avoiding hazards are limited. Drivers should follow the applicable lighting, speed, lane and following-distance rules and pay attention to emergency exits, traffic signals and variable-message signs.

Collier Tunnel on U.S. Route 199. (Del Norte County, California, United States)
Wikimedia.org • Akampfer • CC BY-SA
What should I check before entering a tunnel in the United States?

Rules depend on the state and tunnel operator. For example, the Blue Ridge Parkway advises low-beam headlights and checking vehicle height against each tunnel’s clearance while remaining in your lane.

🔗 nps.gov • National Park Service — Blue Ridge Parkway tunnel clearance and low-beam advice

🔗 mutcd.fhwa.dot.gov • FHWA MUTCD11th Edition including Revision1 — relevant signs/markings; device standard, not state law

Does a tunnel sign in the United States set a universal speed limit?

No single speed can be read from the tunnel pictogram. Apply the road’s relevant limit and any permanent or electronic speed restriction, and drive more slowly when visibility, queues or another hazard require it.

🔗 nps.gov • National Park Service — Blue Ridge Parkway tunnel clearance and low-beam advice

🔗 mutcd.fhwa.dot.gov • FHWA MUTCD11th Edition including Revision1 — relevant signs/markings; device standard, not state law

Warning for a tunnel. Warning for a tunnel.

English • SW37(CA) • Tunnel ahead. Warns of a tunnel ahead. Adjust your speed and follow the tunnel's traffic controls. California design, documented in the Caltrans sign specifications and the 2026 California MUTCD.

Sources

🔗 Commons.wikimedia.org
🔗 Dot.ca.gov • Caltrans: SW37(CA) specification
🔗 Dot.ca.gov • Caltrans: 2026 California MUTCD, section2C.18

SVG source: California Department of Transportation • Public domain • Original revision 2024-05-22. Wikimedia original unmodified.

Is every tunnel in the United States open to pedestrians and cyclists?

No. Check the road category and access signs before entering. A motorway tunnel, a vehicle-restricted tunnel and a purpose-built walking or cycling underpass have different access arrangements. Emergency evacuation routes do not establish ordinary public access.

🔗 nps.gov • National Park Service — Blue Ridge Parkway tunnel clearance and low-beam advice

🔗 mutcd.fhwa.dot.gov • FHWA MUTCD11th Edition including Revision1 — relevant signs/markings; device standard, not state law

1 United States 2 Motorway 3 Expressway 4 Speed limit 5 Minimum speed 6 Advisory speed 7 Bike path 8 Pedestrian warning 9 Tunnel 10 Bridge 11 Speed bump 12 Toll road 13 One-way traffic 14 Slope 15 Bus lane 16 Bus stop 17 Dead end 18 Stop sign 19 Give way 20 Roundabout 21 Road narrowing 22 Pedestrian crossing 23 Railway crossing 24 Mandatory direction 25 Turn prohibition 26 School area 27 Crossing animals 28 Slippery road 29 Rockfall 30 Aircraft 31 Curve 32 Chevron 33 Wrong-way driving 34 Roadworks 35 Height limit 36 Weight limit 37 Radar speed sign 38 Selective barriers 39 Traffic lights 40 Traffic lights warning 41 Pedestrian lights 42 Road markings 43 Bike box 44 Speed feedback 45 Driving licence 46 Traffic mirror 47 Emergency telephone 48 Cycling route 49 Parking 50 No parking 51 No stopping 52 Parallel parking 53 Park and ride 54 Kiss and ride 55 Disabled parking 56 Traffic management 57 Reversing 58 U-turn 59 Carpool 60 Detour 61 Uncontrolled crossroad 62 Ramp 63 Exit 64 Horse riding 65 Emergency exit 66 Runaway truck ramp 67 Oversize load 68 City limit 69 Tourist attraction 70 Horn 71 Axle weight limit 72 Licence plate 73 Charging station 74 Flooding 75 Dip 76 Horse 77 Local traffic 78 Pedestrian 79 Cyclist 80 Motorcycle 81 Truck 82 Bus 83 Police 84 Ambulance 85 Police signals 86 Gravel road 87 Pothole 88 Median strip 89 Public property 90 Path 91 Particulates 92 Air pollution 93 Interchange 94 Rush hour 95 Filling station 96 Road code 97 Two-way traffic 98 Passing lane 99 Street gutter 100 Road debris ...