Transportation Learning HubFree calculator
Taper Length Calculator — PE Civil Transportation Worked Example
A merging taper moves traffic laterally across a lane width W at speed S. Enter the offset width and the speed; the tool applies the taper formula for the speed range and counts the channelizing devices on the taper using the spacing rule stated below.
For study and checking only. This calculator runs entirely in your browser — nothing is sent anywhere. It is meant to verify your hand calculations while you study; on the exam you will work by hand with the NCEES reference handbook.
Quick answer: the merging taper formulas
\[L = W\,S \quad (S \ge 45\ \text{mph}) \qquad L = \frac{W\,S^{2}}{60} \quad (S \le 40\ \text{mph})\]
Two forms, chosen by speed — using the high-speed form at low speed overstates the length, which is the planted error. This tool counts devices with the rule used in the hub’s worked example: devices spaced at the speed in feet, with a device at each end of the taper, so \(N = L/S + 1\).
How to use it — and how to sanity-check the answer
Confirm which taper you are sizing — merging tapers use the full length; shifting and shoulder tapers use fractions of it in the standard taper family, and the exam stem states the type. Sanity-check the device count: spacing in feet equals the speed in mph under the stated rule, so a 600-ft taper at 50 mph carries devices every 50 ft — 12 spaces, 13 devices including both ends.
Worked example (reproduces in the tool above)
Worked example Merging taper and device count
Given: A lane closure on a road with a speed of 50 mph closes one 12-ft lane. The given rule for this problem is that channelizing devices on the taper are spaced at the speed in feet, with a device at each end.
Solution:
- Speed is 50 mph (≥ 45), so \(L = W \times S = 12 \times 50 = 600\) ft.
- Device spacing \(= 50\) ft, so the taper has \(600/50 = 12\) spaces and \(12 + 1 = 13\) devices.
Answer: Taper length \(600\) ft; \(13\) devices.