Signals & Pavement Markings

Study questions with answers

7 sample Signals & Pavement Markings questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.

1. 1. In a dual air system, when should the low air pressure warning come on?

   Correct answer: Before either system's pressure sinks below 60 psi

   The warning light and buzzer must activate before pressure in either the primary or secondary system falls under 60 psi; if it does while driving, stop and park safely.

   Source: South Carolina CDL Manual — Section 5.2: Dual Air Brake

2. 2. How does a 'wig wag' low-pressure warning device alert the driver?

   Correct answer: It drops a mechanical arm into the driver's view

   The wig wag lowers a mechanical arm into view when pressure falls below 60 psi; an automatic one lifts back out of view once pressure climbs above 60 psi again.

   Source: South Carolina CDL Manual — Section 5.1.11: Low Air Pressure Warning

3. 3. On many large buses, at what pressure do the low air pressure warning devices commonly signal?

   Correct answer: At 80 to 85 psi

   While most vehicles warn before 60 psi, large buses often have their low-pressure warnings set to signal at a higher 80 to 85 psi.

   Source: South Carolina CDL Manual — Section 5.1.11: Low Air Pressure Warning

4. 4. A visible low air pressure warning must come on before tank pressure falls below what level on most vehicles?

   Correct answer: 60 psi

   The warning you can see is required to activate before pressure drops under 60 psi (or half the governor cut-out on some older vehicles).

   Source: South Carolina CDL Manual — Section 5.1.11: Low Air Pressure Warning

5. 5. Where would you look for the ABS malfunction lamp on a trailer?

   Correct answer: On the left side, at a front or rear corner, in yellow

   Trailers carry a yellow ABS malfunction lamp on the left side, either at a front or rear corner; tractors, trucks, and buses show theirs on the instrument panel.

   Source: South Carolina CDL Manual — Section 5.1.16: Antilock Braking Systems (ABS)

6. 6. What is the purpose of the stop light switch in an air brake system?

   Correct answer: To turn on the brake lights when the brakes are applied

   A switch operated by air pressure lights the brake lamps the instant you apply the brakes, alerting the drivers behind you.

   Source: South Carolina CDL Manual — Section 5.1.12: Stop Light Switch

7. 7. What does a supply pressure gauge tell the driver?

   Correct answer: How much air pressure is stored in the tanks

   Every air brake vehicle has a gauge showing tank pressure; a dual system shows each half, either with two gauges or one gauge with two needles.

   Source: South Carolina CDL Manual — Section 5.1.9: Supply Pressure Gauges