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Topic 4 · Section 15

Matching Flow of Traffic

🚘 Match the Speed of Surrounding Traffic

  • It’s generally safest to travel at the same speed as traffic (within the legal limit).
  • If the posted speed is 65 mph and most cars are going 65, that’s ideal.
  • Driving significantly slower without reason can be dangerous — others may tailgate or pass unsafely.
  • If you prefer to go slower, stay in the right lane so faster vehicles can pass.
  • Impeding traffic (driving too slowly without cause) can result in a citation.

🌊 Hydroplaning

  • Happens when your tires lose contact with the road due to water buildup.
  • Signs: steering feels light or unresponsive.
  • What to do:
    • Ease off the accelerator.
    • Do NOT brake hard.
    • Make small steering corrections if necessary.
    • Let the vehicle gradually slow down until tires regain grip.

🔄 Sharp Corners / Blind Turns

  • Slow down enough that you could stop safely if there’s something unexpected ahead (e.g., pedestrian, stalled car).
  • Follow posted advisory speeds — they’re there for a reason.

📉 Avoid “Speed Creep”

  • On open roads, you may accidentally speed because lower speeds feel slow.
  • Glance at your speedometer periodically, especially:
    • After exiting a highway.
    • When transitioning into residential or school zones.

⚠️ Basic Speed Law Reminder

  • You can be ticketed for driving the speed limit if it’s unsafe for current conditions (rain, fog, congestion).
  • You can also be cited for going too slow without reason and impeding traffic.

Key principle: Ask yourself:
“Given the road, weather, and traffic, is my speed appropriate?”


💥 Speed and Crash Risk

  • Crash energy increases exponentially with speed.
  • At 60 mph, the crash energy is 4x greater than at 30 mph.
  • Even a small reduction in speed can make a crash far less severe — or avoidable altogether.

Check you have it

179 practice questions cover defensive driving and safe driving practices, each explaining the reasoning behind its answer.

Practise this topic

Source: California Driver's Handbook (DL 600, rev. 6/2025). Edited by Fernando Aguilera. Aprobify is not affiliated with the California DMV.

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