Construction Zone Traffic Control (C-31) · Lesson 1 of 6

Merging Taper Length and Cone Count

"Merging Taper Length and Cone Count" is lesson 1 of 6 in the Construction Zone Traffic Control (C-31) Learning Hub. It opens with "Why the Taper Length Is Calculated, Not Guessed" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Why the Taper Length Is Calculated, Not Guessed
  2. The Two Formulas (Table 6B-4)
  3. Other Tapers Are Fractions of L
  4. How Far Apart the Devices Go (Table 6K-101(CA))
  5. Count the Devices

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Pick the formula" through "Work out the companion tapers if the plan calls for them".

What you'll be able to do

  • Explain the main idea of "Merging Taper Length and Cone Count" in plain language you can use on the exam.
  • Apply this step with confidence: "Other Tapers Are Fractions of L".
  • Apply this step with confidence: "How Far Apart the Devices Go (Table 6K-101(CA))".
  • Apply this step with confidence: "Count the Devices".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Merging Taper Length and Cone CountPLAN VIEW (not to scale)CLOSEDTRAFFICL = 245 ftW =12 ft35 ft max spacing8 cones = 7 spaces + 1merging taper, 12-ft lane at 35 mphSTEP 1 - TAPER LENGTH35 mph is 40 or less, so:L = W x S² / 60L = 12 x 35² / 60L = 12 x 1,225 / 60L = 245 ftSTEP 2 - DEVICESTaper spacing at 35 mph = 35 ft245 / 35 = 7 spaces7 + 1 = 8 cones45 mph or more: L = W x S12-ft lane at 35 mph: 245-ft merging taper, cones 35 ft apart8 cones in the merging taperCompanion tapers: shifting L/2 = 123 ft, shoulder L/3 = 82 ftSource: CA MUTCD 2026 Tables 6B-3(CA), 6B-4, 6K-101(CA); 2025 Caltrans Standard Plan T9 Table 1CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Why the Taper Length Is Calculated, Not Guessed

A merging taper is the diagonal row of channelizing devices that pushes traffic out of a closed lane. The CA MUTCD 2026 Section 6B.08 says a merging taper needs the longest distance of any taper because drivers must merge into common road space, so it has to be long enough for them to see the warning, slow down and move over before the taper ends. It also warns that longer is not automatically better: very long tapers encourage sluggish driving and late lane changes. That is why the manual gives a formula instead of one fixed number.

Step 2: The Two Formulas (Table 6B-4)

Taper length L, in feet, depends on speed S (mph) and offset width W (feet). At 40 mph or less, L = W x S x S / 60. At 45 mph or more, L = W x S. W is the sideways distance traffic must move: a closed 12-foot lane is W = 12. S is the posted speed, the off-peak 85th-percentile speed before work started, or the anticipated operating speed (CA MUTCD 2026 Table 6B-4). Notice the jump at the 40/45 boundary: for a 12-foot offset the taper goes from 320 feet at 40 mph to 540 feet at 45 mph.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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