Roadside and Cross-Section Design

The road from one right-of-way line to the other: lanes, shoulders, curbs and cross slopes; the forgiving roadside beyond them; the barriers that shield what cannot be moved; and the sidewalks, bike lanes and paths alongside. It carries 7–11 of the 80 questions on the Transportation exam, and it is worked largely from the supplied standards.

What the problems look like

Lookup-and-judge problems, usually on a typical section or a plan. Recurring shapes — clear-zone distance, with non-recoverable slopes and curves; which object lies inside it; barrier selection by dynamic deflection; flare rate, length of need and placement on slopes and behind curbs; terminals and crash cushions; Green Book section checks ("which element doesn't conform?"); and bike and pedestrian details — sidewalks, refuges, curb extensions, bike lanes.

By exam day you should be able to —

• find a clear zone and lay out the runout area past a non-recoverable slope;
• rank the treatments for an obstacle: remove, make traversable, relocate, breakaway, shield, delineate;
• choose a barrier system for the space behind it, then set its flare and length of need;
• check a typical section's lane, shoulder and border widths and cross slopes against the right Green Book table and text;
• size a median refuge and lay out bike lanes at an intersection approach.

Where people lose points

• Table entry: enter with the design speed, not the posted limit, the right design-volume band, and the table for the road's own functional class and setting.
• Measure from the right edge: clear zone and shy line run from the edge of the traveled way, not the shoulder; deflection space runs from the barrier to the face of the object it shields, not from the shoulder edge.
• Clear-zone geometry: a non-recoverable slope doesn't count, so the runout area continues past its toe; the curve adjustment applies on the outside of a curve only; and a hazard's lateral extent in the length-of-need equation stops at the clear-zone edge.
• Cross slope on a curve: on the high side of a superelevated section the lane and shoulder slopes add — check the algebraic difference, not the shoulder slope alone.
• Curbs aren't barriers: a curb has no significant redirection capability, so it does not stand in for clear zone or barrier, and it limits where a barrier can sit behind it.

Have these at your fingertips

Roadside Design Guide Chapters 3 (roadside topography and the clear zone), 4 (breakaway supports, poles and trees), 5 (roadside barriers) and 8 (end treatments); Green Book Chapter 4 and the functional-class chapters' section tables; and MUTCD Part 9 for bicycle facilities. The MUTCD edition you are supplied depends on your appointment date — the 2009 edition before the April 2027 exam, the 11th from it — so work from the edition listed for your exam window.

Going deeper

• Transportation design standards: the April 2027 HCM and MUTCD change
• Horizontal Design — the superelevation that sets the shoulder break and the curve clear zone

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.