Idaho CDL — General Knowledge practice
Idaho CDL — General Knowledge: Signals & Pavement Markings practice test
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 · August 12, 2026
14 questions · pass with 11 correct. You get instant feedback and an explanation after every answer.
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12 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.
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1. Safety forces you to move Division 1.1 explosives between two vehicles while on a public road. What must you set out to warn others?
Correct answer: Electric lanterns, flags, or red warning reflectors
Explosives in the three most dangerous divisions may be moved between vehicles on a public road only in an emergency, and then the driver must put out red reflectors, flags or electric lanterns as a warning.
Source: Idaho Commercial Driver's License Manual — Section 9.4.1, General Loading Requirements
2. Besides color coding, how are a tractor's trailer air lines sometimes identified so they get coupled correctly?
Correct answer: By metal tags stamped 'service' and 'emergency'
Blue is used for service lines and red for emergency lines, and some lines also carry metal tags with 'service' or 'emergency' stamped into them.
Source: Idaho Commercial Driver's License Manual — Section 6.2.5, Hose Couplers (Glad Hands)
3. Your oil pressure gauge shows pressure that is low, dropping or fluctuating. What does the manual's gauge illustration tell you to do?
Correct answer: Stop immediately, because an engine without oil can be destroyed quickly
The oil pressure illustration marks low, falling or fluctuating pressure with an instruction to stop at once, because an engine running without oil can be ruined in a very short time.
Source: Idaho Commercial Driver's License Manual — Section 2.1.5, Seven-step Inspection Method (Figure 2.5)
4. Why does the inspection guide have you check the electric lines running from the power unit to the trailer for damage?
Correct answer: Damaged lines can leave the trailer without turn signals or brake lights, so others can't tell what you are about to do
The guide warns that damaged electric lines can cost the vehicle its ability to communicate maneuvers, leaving no turn or brake lights, and that not being seen at night is a serious hazard.
Source: Idaho Commercial Driver's License Manual — Section 11.6.1, Combination Vehicles Only
5. During a bus inspection, with the key in the 'on' position, what do you check about the emergency exits?
Correct answer: That the emergency exit warning devices work
Besides confirming the exits are labeled, undamaged and work smoothly, the inspection has you turn the key on and confirm the exit warning devices operate.
Source: Idaho Commercial Driver's License Manual — Section 11.2, Passenger and School Bus Only
6. According to the oil pressure gauge illustration in the manual, what is the normal reading while the engine is operating rather than idling?
Correct answer: 35 to 75 psi
The illustration shows 5 to 20 psi at idle and 35 to 75 psi while operating.
Source: Idaho Commercial Driver's License Manual — Section 2.1.5, Seven-step Inspection Method (Figure 2.5)
7. As part of securing a school bus for an evacuation, which lights does the manual tell the driver to switch on?
Correct answer: The hazard-warning lights
Securing the bus for an evacuation means putting it in Park or Neutral, applying the parking brakes, turning the engine off, taking the key and switching on the hazard-warning lights.
Source: Idaho Commercial Driver's License Manual — Section 10.3.2, Evacuation Procedures
8. A shipping paper lists ordinary freight along with hazardous materials. Besides entering the hazardous items first or highlighting them in a contrasting color, how may they be identified?
Correct answer: By putting an 'X' ahead of the description, in a column headed 'HM'
Hazardous entries must be listed first, highlighted, or marked with an X in the HM column. RQ may take the place of the X when a reportable quantity has to be identified.
Source: Idaho Commercial Driver's License Manual — Section 9.3.5, The Item Description
9. On some older vehicles the tractor protection valve is worked by a lever instead of a knob. Which lever position do you use to tow a trailer?
Correct answer: The 'normal' position
On older vehicles 'normal' is the towing position, while 'emergency' cuts off the air supply and applies the trailer's emergency brakes.
Source: Idaho Commercial Driver's License Manual — Section 6.2.3, Trailer Air Supply Control
10. The service air line between a tractor and its trailer goes by two other names. What are they?
Correct answer: The control line or signal line
Control line and signal line are both alternate names for the service line, which carries air governed by the brake pedal or the trailer hand valve. 'Supply line' is another name for the emergency line.
Source: Idaho Commercial Driver's License Manual — Section 6.2.4, Trailer Air-lines
11. On a crowded transit bus, a rider stands next to the driver's seat, ahead of the standee line, to chat. Is that allowed?
Correct answer: No; standing riders must stay behind the standee line, which keeps them back of the driver's seat
Riders may not stand ahead of the back of the driver's seat. Buses built for standees mark that limit with a floor line, and everyone standing has to remain behind it.
Source: Idaho Commercial Driver's License Manual — Section 4.2.3, Standee Line
12. On large buses, at about what pressure is it common for the low air pressure warning devices to signal?
Correct answer: 80 to 85 psi
Most vehicles must give a visible warning before tank pressure falls below 55 psi, but the manual notes that the warning devices on large buses commonly come on at 80 to 85 psi.
Source: Idaho Commercial Driver's License Manual — Section 5.1.11, Low Air Pressure Warning
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