Section 7: Doubles and Triples - California DMV

Overview

• Purpose: Information for the CDL knowledge test for driving double and triple trailers safely.
• Key Focus: Handle with care, correct coupling/uncoupling, and inspecting trailers thoroughly.
• Legal Note: Triples illegal in California but covered for knowledge on other states.
• Endorsement: Knowledge test only, no need for a set of doubles in the skills test.

7.1 Pulling Double/Triple Trailers

• Stability: Less stable and more prone to issues than single CMVs.

7.1.1 Prevent Trailer Roll Over

• Use gentle steering.
• Slow down around corners, ramps, and curves.

7.1.2 Crack-the-Whip Effect

• More likely to turn over due to this effect.
• Steer gently, especially the last trailer susceptible.

7.1.3 Inspect Completely

• Check all critical parts.

7.1.4 Look Far Ahead

• Drive smoothly to avoid rollovers or jackknifes.

7.1.5 Manage Space

• Allow more space for doubles/triples.
• Need larger gaps for traffic maneuvers.

7.1.6 Adverse Conditions

• Be cautious in bad weather and mountain driving.

7.1.7 Parking the Vehicle

• Avoid difficult escape spots.

7.1.8 ABS on Converter Dollies

• Required for dollies built after March 1, 1998.

7.2 Coupling and Uncoupling

• Importance: Correct procedure essential for safety.

7.2.1 Coupling Double Trailers

• Secure Rear Trailer: Ensure emergency brakes are set or chock wheels.
• Position Converter Dolly: Align with kingpin and ensure all secure.
• Connect and Test: Ensure all connections are secure and brakes work.

7.2.2 Uncoupling Double Trailers

• Uncouple Rear Trailer: Follow safety measures.
• Uncouple Converter Dolly: Follow procedures to avoid injury.

7.2.3 Coupling and Uncoupling Triple Trailers

• Legal Note: Not allowed in California.

7.2.4 Other Combinations

• Coupling/uncoupling varies with different vehicle types.

7.3 Inspecting Doubles and Triples

• 7-step Inspection: Follow Section 2 guidelines.

7.3.1 Additional Checks

• Coupling System: Ensure all connections and attachments are secure.
• Landing Gear: Fully raised and not damaged.
• Doubles/Triples Specific: Check all valves, lines, and connections.

7.3.2 Walk Around Inspection

• Additional checks combined with Section 5 for air brakes.

7.4 Doubles/Triples Air Brake Check

• Follow Section 6 for combination vehicles.

7.4.1 Additional Air Brake Checks

• Air Flow Check: Ensure air reaches all trailers.
• Tractor Protection Valve: Test functionality.
• Trailer Emergency/Service Brakes: Ensure proper function and connection.

Test Your Knowledge

• Various questions to test understanding of handling, coupling, uncoupling, and safety checks.