Traffic Signs & Signals — District of Columbia
District of Columbia CDL practice test: 423 free practice questions (Based on the official driver handbook). The official format is not yet verified; check the official site before your test. Traffic Signs & Signals: 2 questions.
Regulatory, warning and guide signs, plus traffic light and pavement marking questions.
This topic page is still being reviewed against the official handbook. Until review is finished it is hidden from search engines.
| Topic / Metric | Value |
|---|---|
| Topic | Traffic Signs & Signals |
| License test | District of Columbia CDL permit (CLP) knowledge tests |
| Topic questions | 2 (0% of 423 total) |
| Review status | This topic page is still being reviewed against the official handbook. Until review is finished it is hidden from search engines. |
Official handbook
Not yet verified
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Questions (2)
1. What does the trailer air supply control look like?
- It is a square blue knob.
- It is a triangular yellow knob.
- It is an eight-sided red knob. ✓
- It is a circular orange knob.
Answer: C. It is an eight-sided red knob.
The trailer air supply control on newer vehicles is a red eight-sided knob. The handbook describes the trailer air supply control in the cab, which operates the tractor protection valve. On newer vehicles it is a red knob with eight sides. You push it in to send air to the trailer and pull it out to cut the air off and apply the trailer emergency brakes. The same knob pops out on its own when air pressure falls to roughly 20 to 45 psi, closing the tractor protection valve. Older vehicles may instead have a lever rather than a knob.
2. A vehicle stopped at a green light may indicate that the driver:
- Is impaired. ✓
- Is colorblind.
- Does not know the rules of the road.
- Is very patient.
Answer: A. Is impaired.
A vehicle stopped at a green light may indicate that the driver is impaired. The handbook lists stopping at a green light, along with waiting too long at a stop, as stopping at the wrong time. It places that behavior with weaving, drifting, and leaving the road, actions that show a driver is not responding normally to the traffic situation. Among the choices, impairment fits a driver who fails to go on a green signal; the passage does not tie the stop to colorblindness, rule ignorance, or patience.
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Last checked: 2026-10-17 · Verified from official source
Updated: · Based on the official driver handbook