{"id":13213,"date":"2020-04-15T15:06:35","date_gmt":"2020-04-15T22:06:35","guid":{"rendered":"https:\/\/www.dmv.ca.gov\/portal\/handbook\/commercial-driver-handbook\/section-7-doubles-and-triples\/"},"modified":"2022-03-30T11:35:58","modified_gmt":"2022-03-30T18:35:58","slug":"section-7-doubles-and-triples","status":"publish","type":"dmv_handbook","link":"https:\/\/www.dmv.ca.gov\/portal\/es\/handbook\/commercial-driver-handbook\/section-7-doubles-and-triples\/","title":{"rendered":"Section 7: Doubles and Triples"},"content":{"rendered":"

This section has information you need to pass the CDL knowledge test for driving safely with double and triple trailers. It tells about how important it is to be very careful when driving with more than 1 trailer, how to couple and uncouple correctly, and about inspecting doubles and triples carefully. (You should also study Sections 2<\/a>, 5<\/a>, y 6<\/a>.)<\/p>\n\n\n\n

Note<\/span> Triple combinations are not legal in California. Triples are discussed in this section because they are legal in many other states.<\/span><\/p>\n\n\n\n

The endorsement is given by knowledge test only. Do not bring in a set of doubles<\/strong> for a Class A skills test.<\/p>\n\n\n\n

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7.1 \u2013 Pulling Double\/Triple Trailers<\/h3>\n\n\n\n

Take special care when pulling 2 and 3 trailers. There are more things that can go wrong, and doubles\/triples are less stable than other CMVs. Some areas of concern are discussed below.<\/p>\n\n\n\n

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7.1.1 \u2013 Prevent the Trailer From Rolling Over<\/h3>\n\n\n\n

To prevent trailers from rolling over, you must steer gently and go slowly around corners, on ramps, off ramps, and curves. A safe speed on a curve for a straight truck or a single trailer combination vehicle may be too fast for a set of doubles or triples.<\/p>\n\n\n\n

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7.1.2 \u2013 Beware of the Crack-the-Whip Effect<\/h3>\n\n\n\n

Doubles and triples are more likely to turn over than other combination vehicles because of the \u201ccrack-the-whip\u201d effect. You must steer gently when pulling trailers. The last trailer in a combination is most likely to turn over. If you do not understand the crack-the-whip effect, study Subsection 6.1.2 of this handbook.<\/p>\n\n\n\n

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7.1.3 \u2013 Inspect Completely<\/h3>\n\n\n\n

There are more critical parts to check when you have 2 or 3 trailers. Check them all. Follow the procedures described later in this section.<\/p>\n\n\n\n

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7.1.4 \u2013 Look Far Ahead<\/h3>\n\n\n\n

Doubles and triples must be driven very smoothly to avoid rollover or jackknife. Therefore, look far ahead so you can slow down or change lanes gradually when necessary.<\/p>\n\n\n\n

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7.1.5 \u2013 Manage Space<\/h3>\n\n\n\n

Doubles and triples take up more space than other CMVs. They are not only longer, but also need more space because they cannot be turned or stopped suddenly. Allow more following distance. Make sure you have large enough gaps before entering or crossing traffic. Be certain you are clear at the sides before changing lanes.<\/p>\n\n\n\n

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7.1.6 \u2013 Adverse Conditions<\/h3>\n\n\n\n

Be more careful in adverse conditions. In bad weather, slippery conditions, and mountain driving, you must be especially careful if you drive double and triple bottoms. You will have greater length and more dead axles to pull with your drive axles than other drivers. There is more chance for skids and loss of traction.<\/p>\n\n\n\n

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7.1.7 \u2013 Parking the Vehicle<\/h3>\n\n\n\n

Make sure you do not get in a spot you cannot pull straight through. You need to be aware of how parking lots are arranged in order to avoid a long and difficult escape.<\/p>\n\n\n\n

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7.1.8 \u2013 Anti-lock Braking Systems on Converter Dollies<\/h3>\n\n\n\n

Converter dollies built on or after March 1, 1998, are required to have anti-lock brakes. These dollies have a yellow lamp on the left side of the dolly.<\/p>\n\n\n\n

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7.2 \u2013 Coupling and Uncoupling<\/h3>\n\n\n\n

Knowing how to couple and uncouple correctly is basic to safe operation of doubles and triples. Wrong coupling and uncoupling can be very dangerous. Coupling and uncoupling steps for doubles and triples are listed below.<\/p>\n\n\n\n

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7.2.1 \u2013 Coupling Double Trailers<\/h3>\n\n\n\n

Secure the Second (Rear) Trailer<\/em><\/h3>\n\n\n\n

If the second trailer does not have spring brakes, drive the tractor close to the trailer, connect the emergency line, charge the trailer air tank, and disconnect the emergency line. This will set the trailer emergency brakes (if the slack adjusters are correctly adjusted). Chock the wheels if you have any doubt about the brakes.<\/p>\n\n\n\n

For the safest handling on the road, the more heavily loaded semitrailer should be in first position behind the tractor. The lighter trailer should be in the rear.<\/p>\n\n\n\n

A converter gear on a dolly is a coupling device of 1 or 2 axles and a fifth-wheel by which a semitrailer can be coupled to the rear of a tractor-trailer combination forming a double bottom rig. See Figure 7.1.<\/p>\n\n\n\n

\"a<\/figure>\n\n\n\n

Figure 7.1 <\/strong><\/p>\n\n\n\n

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Position the Converter Dolly in Front of the Second (Rear) Trailer<\/em><\/h3>\n\n\n\n