Merge Taper Length Calculator

This calculator uses a widely applied work zone taper approach based on speed and lane width.

• Merge taper (lane drop or merge): For speeds up to 40 mph L = W × S
• Merge taper (higher speeds): L = W × S² ÷ 60
• Shift taper (optional): For speeds up to 40 mph L = 2 × W × S
• Shift taper (higher speeds): L = W × S² ÷ 30

Where L is taper length (ft), W is lane width (ft), and S is speed (mph). Inputs entered in metric units are converted internally.

1. Enter the design or posted speed and choose its unit.
2. Enter the lane width to be tapered and choose its unit.
3. Select Merge for lane closures or Shift for lateral shifts.
4. Pick your rounding preference for reporting.
5. Click Calculate to display results above the form.
6. Use the CSV or PDF buttons to export the computed report.

A merge taper provides a controlled lateral transition so drivers leave a closing lane without sudden steering. Longer tapers lower side friction demand, reduce encroachment, and improve queue stability where volumes are high. The computed length is a planning baseline, then refined for sight distance, lighting, and channelization spacing.

Key Inputs and Units

This calculator uses design speed and the effective width being shifted, typically a full lane width. Speed can be entered in mph or km/h and width in feet or meters, then converted internally to maintain consistent equations. Field widths should reflect the traveled way, not shoulder striping, unless traffic is guided onto that area.

Interpreting Taper Length Results

For lower speeds the relationship is linear, producing practical values for urban streets. At higher speeds the squared-speed form increases length rapidly, reflecting reduced driver reaction margin. The ratio output (1:n) shows how gradual the taper is; larger n indicates a longer transition for the same width. Compare the computed length with available approach distance so the merge does not spill into intersections, ramps, or driveways.

Applying Standards in Work Zones

Agencies commonly follow MUTCD-style guidance for merge and shift tapers in temporary traffic control. Merge tapers are used for lane drops and merges near the activity area. Shift tapers are longer because they move traffic laterally while keeping the same number of lanes, often upstream of barriers or narrowed sections. Select merge versus shift based on whether lanes are reduced or only repositioned, and keep downstream alignment clear with adequate buffer spacing.

Quality Checks and Field Tips

Verify that the taper fits within available distance and that upstream signs and cone spacing are coordinated. Consider heavy vehicles, wet pavement, and nighttime conditions that may justify added length. Check that delineator spacing supports driver path guidance, and avoid placing devices where drainage or uneven pavement could tip them. Always coordinate with project traffic control plans, standards, and field supervision before installation.

1) What is a merge taper in temporary traffic control?

A merge taper is a line of devices that guides traffic out of a closed lane into an open lane using a gradual lateral transition, reducing sudden steering and side-swipe risk.

2) When should I choose shift instead of merge?

Choose shift when the number of lanes stays the same but traffic must move laterally, such as around barriers, narrow bridges, or work areas that pinch the alignment.

3) Which speed should I enter?

Use the posted speed if it reflects typical operating speed. If a traffic control plan specifies a design speed, enter that value to match the intended taper layout.

4) What width should I use if the closure is partial?

Use the effective lateral offset drivers must travel, such as a narrowed lane shift or partial lane closure width. Measure the distance between centerlines or edge lines as used in the plan.

5) Why does the formula change above 40 mph?

At higher speeds, drivers need more distance to perceive, react, and merge smoothly. The squared-speed relationship increases taper length faster to reflect reduced reaction time margins.

6) Do I still need to follow local standards?

Yes. This calculator provides a common baseline, but agencies may require minimum lengths, device spacing rules, or special treatments for grades, curves, and high truck percentages.

• Local agencies may require different taper policies or minimum lengths.
• Consider site constraints, traffic mix, and visibility when finalizing designs.
• Always verify work zone layouts with your project specifications.