SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/drive-hov-diamond

A white diamond painted in a highway lane marks what kind of lane?

A carpool (HOV) lane for vehicles meeting the posted occupancy rule.

  1. A carpool or HOV lane ✔
  2. A truck-only lane
  3. A lane that ends soon

Why: The diamond marks a high-occupancy vehicle lane. Signs tell you how many people must be in the car and the hours it is in effect.

Huh, didn't know that: A number after the diamond, like a 2 or 3, can show how many people the lane requires.

The dad joke
Why is the carpool lane marked with a diamond? Because friends are precious.
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References

Answer: A carpool or HOV lane. The diamond marks a high-occupancy vehicle lane. Signs tell you how many people must be in the car and the hours it is in effect.

  1. California Driver's Handbook, Section 6 www.dmv.ca.gov/portal/handbook/california-driver-handbook/navigating-the-roads
    The road surface in a HOV lane is marked with a diamond symbol and the words Carpool Lane.
    Checked 2026-10-09.
  2. MUTCD 11th Edition with Revision 1, Section 3E.03 mutcd.fhwa.dot.gov/pdfs/11th_Editionr1/mutcd11theditionr1hl.pdf
    A numeral indicating the vehicle occupancy requirements established for a high-occupancy vehicle lane may be included in sequence after the diamond symbol
    Checked 2026-10-09.

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Test yourself in the game

Cars & DrivingYour lane line changes from long dashes to short, closely spaced dots. What is it warning you about?Cars & DrivingTwo solid white lines separate your lane from a carpool lane. May you cross them?Cars & DrivingWhich lane should a normal right turn begin and end in?

That's stuff everyone should know.