Work Zone Longitudinal Buffer Space and Activity Area Length (MUTCD 6B.06)
How long a lane closure's buffer space is, how far apart the drums go, and how long the whole closure runs.
Example
You enter
- Speed: posted, off-peak 85th percentile, or anticipated (mph) 35
- Work space length (ft) 400
- Width of the lane closed (ft) 12
- Downstream taper (ft, 50 to 100) 50
- Shadow vehicle or arrow board ahead of the work space (ft, 0 if none) 0
You get
- Buffer (ft) 250
- Merging taper (ft) 245
- Buffer devices 5
- Work devices 6
- Closure (ft) 945
Checked against published worked examples from: FHWA.
Details, formula, and sources
ScopeHow long a lane closure's buffer space is, how far apart the drums go, and how long the whole closure runs, by the MUTCD 11th Edition. Section 6B.06 sizes an optional longitudinal buffer by stopping sight distance from Table 6B-2, 115 ft at 20 mph up to 820 ft at 75 mph, and nothing is stored or worked in it. Section 6K.01 spaces channelizing devices no more than 1 ft per mph apart along a taper and 2 ft per mph along a tangent. A 35 mph street with a 12 ft lane closed and a 400 ft work space has a 245 ft merging taper, a 250 ft buffer with drums every 70 ft (five, counting both ends), and 945 ft from the first drum to the end of a 50 ft downstream taper; at 55 mph it is a 660 ft taper, a 495 ft buffer and 1,605 ft. A shadow vehicle's offset ahead of the work is added, since only the area upstream of it counts as buffer. The traffic taper length calculator does the tapers in detail; the agency's traffic control plan governs.
Formula or tablebuffer = Table 6B-2 stopping sight distance at the next row at or above the speed (115 ft at 20 mph ... 820 ft at 75 mph); merging taper L = W S^2 / 60 (S <= 40 mph) or W S (S >= 45 mph) when not entered; tangent spacing = 2 S ft, taper spacing = S ft; devices along the buffer = ceil(buffer / 2S) + 1, along the work space = ceil(work / 2S); activity area = buffer + shadow offset + work; closure = L + activity area + downstream taper (50 to 100 ft).
Source and editionMUTCD 11th Edition (FHWA, December 2023 printing, as posted at mutcd.fhwa.dot.gov and read on 2026-10-19): Section 6B.06 paragraphs 11 and 13, Table 6B-2, Table 6B-3, Table 6B-4, and Section 6K.01 paragraphs 4 and 5.
Free accessThe MUTCD is public domain and free at mutcd.fhwa.dot.gov.
What governsEstimate. AHJ and licensed professional govern.
API field namesspeed_mph, work_length_ft, lane_width_ft, downstream_taper_ft, shadow_offset_ft, buffer_ft, merging_taper_ft, buffer_devices, work_devices, closure_ft
- Next row up between speeds a speed between table rows takes the higher rowconservative reading of Table 6B-2
- Device count both ends of the buffer counted; the taper's own devices are the taper calculator'sstated assumption