Traffic Control Design

Putting the right device in the right place: permanent signs and pavement markings, and temporary traffic control through a work zone. It carries 5–8 of the 80 questions on the Transportation exam. The MUTCD governs both subtopics, so speed here comes from knowing where things sit in it.

What the problems look like

Lookups and layout calculations, often from a plan view. Recurring shapes — taper lengths (merging, shifting, shoulder) and the channelizing devices that form them; advance warning sign spacing and buffer space, chained into a station layout back from the work space; the parts of a temporary traffic control zone and what each does; warning-sign placement ahead of a curve and chevron counts around one; no-passing zones on a crest; line colors; and sign size by road type and speed, and mounting height by setting (rural or urban with pedestrians).

By exam day you should be able to —

• name the four TTC zone areas — advance warning, transition, activity, termination — and what each one does to traffic;
• tell a merging, shifting and shoulder taper apart on a drawing and size each from the taper-length formula;
• convert a taper length into a device count at the right spacing;
• lay out a lane closure in stations: warning signs, taper, buffer, work space;
• place warning signs and chevrons for a horizontal curve from the approach speed, its advisory speed and its arc length;
• locate a no-passing zone on a vertical curve from the sight line.

Where people lose points

• Which taper: read the drawing first. A taper that closes only the shoulder is not the merging taper, and a shift that keeps lanes open is not a merge.
• W is the lateral offset, not automatically the lane width.
• The speed band: the taper formula has a low-speed and a high-speed form. The boundary speed belongs to one form only.
• Devices, not spaces: a row of channelizing devices has one more device than gaps, and taper spacing is tighter than tangent spacing.
• Warning-sign spacing: read the right road-type row, and add every spacing, including the one from the transition to the first sign, when you chain a layout back to a station.
• Speed inputs: advance placement of a curve sign reads the approach (posted or 85th-percentile) speed and the curve's advisory speed itself, not the speed drop; chevron spacing reads the advisory speed. A no-passing zone uses the 85th-percentile or posted speed, not the design speed, and its own eye and object heights.
• Colors: yellow separates opposing traffic and marks left-hand edges; white separates same-direction traffic and marks right-hand edges. Check the cases that look like exceptions: a one-way street's left edge is yellow, two-way left-turn and reversible lanes are separated in yellow, and a reversible roadway takes white on both edges.

Have these at your fingertips

The MUTCD's Part 2 (signs), Part 3 (markings) and Part 6 (work zones), and where the taper, spacing and placement tables sit. The MUTCD edition you are given depends on your appointment date, and section and table numbers can move between editions; learn the one your exam supplies.

Going deeper

• Transportation design standards: the April 2027 HCM and MUTCD change
• Horizontal Design — curve geometry for chevron spacing

Part of the Transportation exam. Practice this area with exam-real problems — the tutor walks any one you miss. → Start practicing free — free with an account.