Transportation Learning HubTransportation Learning Hub · PE Civil Transportation · Area 8 of 10
Traffic Control Design — PE Civil Transportation
The language of the road: signs, markings and — when the road is being rebuilt under traffic — the temporary arrangements that guide drivers safely past the work. Most of this area is conceptual (what device, in what order, doing what job), with a small family of taper and spacing calculations on top.
Take the free 3-question mini-quiz ↓
Permanent signs and pavement markings
Signs fall into three families by function. Regulatory signs state the law of the road (stop, yield, speed limits, prohibitions) and are typically black or red on white, or white on red. Warning signs flag conditions ahead (curves, junctions, crossings) and are yellow and diamond-shaped in the main. Guide signs give direction and information (destinations, distances, services) and are green for direction, blue for services, brown for recreation. Shape is a backup channel of information — the octagon and the inverted triangle are recognisable before their legends can be read. Pavement markings carry the same discipline in colour: yellow separates opposing traffic, white separates same-direction traffic and marks the right edge, and markings divide into longitudinal lines (continuous guidance) and transverse markings (stop lines, crosswalks) plus symbols and words.
Regulatory = law · Warning = conditions ahead · Guide = direction and information
Yellow lines: opposing traffic · White lines: same-direction traffic and right edge line
A device must satisfy the basic requirements of traffic control: fulfil a need, command attention, convey a clear and simple meaning, command respect, and give adequate time for response. Questions that describe a confusing, redundant or contradictory device are testing those five requirements.
Temporary traffic control — the four zones
Work zones are laid out as a sequence every driver passes through. The advance warning area tells road users what to expect ahead. The transition area moves traffic from its normal path to the work-zone path, using tapers formed by channelizing devices. The activity area is where the work happens — workspace, protected by buffer space (longitudinal and lateral) that traffic must not enter, with traffic space beside it for vehicles to pass. The termination area returns traffic to normal, ending with devices that mark the end of the temporary control. Flaggers, arrow boards and temporary signals are layered onto this skeleton as the situation demands, and the same zone logic protects workers, drivers and pedestrians simultaneously.
Advance warning → Transition → Activity (buffer + workspace + traffic space) → Termination
| Channelizing devices | cones, tubular markers, drums and barricades that guide traffic and mark the taper or edge |
|---|---|
| Buffer space | empty recovery space between traffic and the workspace; no work, storage or vehicles belong in it |
| Taper | the angled line of devices that shifts traffic laterally; merging, shifting and shoulder tapers differ in length |
Tapers and channelizing devices
The merging taper — the one that closes a lane — is the longest and the one the calculations use. For speeds of 45 mph or more its length is \(L = W \times S\), with \(W\) the lateral shift (usually one lane width) and \(S\) the speed in mph; at lower speeds a shorter formula applies, and shifting tapers (which move traffic across without a merge) are a fraction of the merging length, as a problem statement will specify. Channelizing devices are then spaced along the taper closely enough to read as a continuous guide — a common rule given in problems is a spacing in feet equal to the speed in mph on tapers — and counting devices means counting positions along the length, including both ends.
\[L = W \times S \qquad \text{Number of devices} = \frac{L}{\text{spacing}} + 1\]
| L | merging taper length, ft |
|---|---|
| W | width of the lateral shift (lane width), ft |
| S | speed, mph — used directly in this US customary formula, not converted |
The \(+1\) in the device count is the classic miss: a taper with devices at both ends has one more device than it has spaces.
Worked example Merging taper length 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. Find the merging taper length and the number of devices on the taper.
Solution:
- Taper length: \(L = W \times S = 12 \times 50 = 600\) ft.
- Spacing: 50 ft, so the number of spaces is \(600 / 50 = 12\).
- Devices, counting both ends: \(12 + 1 = 13\).
Answer: Taper length 600 ft; 13 channelizing devices on the taper.