MUTCD taper length calculator

MUTCD 11th Edition Table 6B-4 splits the calculation at the 40/45 mph boundary. Below and at 40 mph the length grows with the square of the speed; at and above 45 mph it grows linearly.

40 mph or less:  L = W × S² ÷ 60
45 mph or more:  L = W × S

L = taper length in feet
W = width of offset in feet
S = posted speed limit, off-peak 85th-percentile speed
    prior to work starting, or anticipated operating speed

Table 6B-3 then applies the criterion for the taper type. A merging taper is at least L, a shifting taper at least 0.5 L, and a shoulder taper at least 0.33 L. The one-lane two-way and downstream tapers are not multiples of L at all — both are 50 feet minimum and 100 feet maximum, with devices at approximately 20-foot spacing.

A utility crew closes one 12-foot lane on a 35 mph city street. The offset W is 12 feet and the speed S is 35 mph, so L = 12 × 35² ÷ 60 = 245 feet. If the closure needs a merging taper, the taper is 245 feet. If traffic only shifts laterally, a shifting taper of 0.5 L is 125 feet (rounded up to the nearest 5 feet, since Table 6B-3 states a minimum).

Channelizing devices in that taper space at no more than 1 × the speed limit in feet, so 35 feet apart — eight cones over a 245-foot merging taper.

MUTCD Section 6B.08 is explicit that longer tapers are not necessarily better, particularly in urban areas with short block lengths or frequent driveways, because extended tapers encourage sluggish operation and lead drivers to delay lane changes. Table 6B-3 states minimums; treat them as the target, not the floor of a range you should exceed.

What is the MUTCD taper length formula?

MUTCD 11th Edition Table 6B-4 gives two formulas. At 40 mph or less, L = W × S² ÷ 60. At 45 mph or more, L = W × S. L is the taper length in feet, W is the width of the lateral offset in feet, and S is the posted speed limit, off-peak 85th-percentile speed prior to work starting, or the anticipated operating speed in mph.

How long should a merging taper be?

At least L, per MUTCD Table 6B-3. A merging taper requires the longest distance of any taper type because drivers have to merge into shared road space.

How long should a shifting taper be?

At least 0.5 L, per MUTCD Table 6B-3. A shifting taper is used when traffic needs a lateral shift rather than a merge.

How long should a shoulder taper be?

At least 0.33 L, per MUTCD Table 6B-3. If the shoulder is used as a travel lane, either through practice or during the work, use a normal merging or shifting taper instead.

How long is a downstream taper?

A minimum of 50 feet and a maximum of 100 feet, with channelizing devices at approximately 20-foot spacing, per MUTCD Table 6B-3 and Section 6B.08. The older "100 feet per lane" rule of thumb is not what the 11th Edition says.

Which table is the taper formula in?

In the MUTCD 11th Edition (December 2023) it is Table 6B-4, with the taper type criteria in Table 6B-3. The 2009 Edition carried the same content as Tables 6C-4 and 6C-3, so older references cite the earlier numbers.