Louisiana CDL — Air Brakes practice
Signals & Pavement Markings
How to read traffic signals, lane lines, and pavement markings — including yellow and white lines, arrows, and flashing lights.
Content reviewed against official driver handbooks · July 7, 2026
6 questions · pass with 5 correct. You get instant feedback and an explanation after every answer.
Study questions with answers
6 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. What does the stop light switch do in an air brake system?
Correct answer: It turns on the brake lights to warn drivers behind you
An air-operated electric switch turns on the brake lights so following drivers know you are braking.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.12 - Stop Light Switch
2. A visible low air pressure warning must come on before tank pressure falls below what level?
Correct answer: 60 psi
The warning signal you can see is required to activate before the air pressure drops under 60 psi.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.11 - Low Air Pressure Warning
3. What does a supply pressure gauge tell the driver?
Correct answer: How much air pressure is in the storage tanks
The supply gauge reads the pressure held in the tanks; a dual system has one for each half, or a single gauge with two needles.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.9 - Supply Pressure Gauges
4. Where is the yellow ABS malfunction lamp located on a trailer?
Correct answer: On the left side, at the front or rear corner
Trailers carry the yellow ABS malfunction lamp on the left side, either the front or rear corner; tractors and trucks show it on the dash.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.16 - Antilock Braking Systems (ABS)
5. What is the 'wig wag' low-air warning device?
Correct answer: A mechanical arm that drops into the driver's view when pressure falls below 60 psi
The wig wag lowers a mechanical arm into the driver's view once system pressure drops below 60 psi.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.11 - Low Air Pressure Warning
6. On large buses, at about what pressure do the low-air warning devices commonly activate?
Correct answer: 80 to 85 psi
It is common for large buses to have their low-pressure warnings trigger at 80 to 85 psi rather than at 60.
Source: Louisiana Commercial Driver's License Manual, Section 5.1.11 - Low Air Pressure Warning
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