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Transportation & Surveying

Passing Sight Distance (AASHTO 2011+)

Passing sight distance for two-lane, two-way highways per the AASHTO 2011+ Green Book single-model design values (Table 3-4, from NCHRP Report 605): PSD and the assumed passing/passed vehicle speeds, with linear interpolation between tabulated design speeds. Use for: 'find the PSD for a design speed of 60 mph', passing-zone design values on two-lane highways. Not for: stopping or decision sight distance, MUTCD no-passing-zone marking warrants (shorter values), or the obsolete pre-2001 four-component PSD model.

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Worked examples

These are the solver's own reference problems — the answers come from published sources or independent hand computation, never from the solver itself. The solution below is the live solver output for each.

Example 1

US 60 mph → PSD 1000 ft (passed vehicle assumed at 48 mph)

Given

design speed
60 mi/h

Assumptions

  • Model: AASHTO 2011+ single-model PSD design values (Green Book Table 3-4, adopted from NCHRP Report 605) — the Green Book publishes design values, not a closed-form equation; the obsolete pre-2001 four-component model is intentionally NOT used.
  • Model assumptions (Green Book): passing and opposing vehicles travel at the design speed; the passed vehicle is 12 mph slower; both vehicles are 19 ft long; 1 s perception-reaction to abort; aborts decelerate at 11.2 ft/s²; 1-s headways and clearance.
  • Sight-distance measurement basis: driver eye height 3.5 ft (1.08 m) to an object height of 3.5 ft (the opposing vehicle).

Solution steps

  1. Assumed maneuver speeds

    The passing (and opposing) vehicle travels at the design speed; the passed vehicle is assumed slower by a fixed differential.

    Vpassed = V − ΔV, with ΔV = 12 mph (US) or 19 km/h (metric)

    V = 60 mi/h; passed vehicle = 60 mi/h − 12 mi/h = 48 mi/h

  2. Design PSD from the AASHTO table

    The 2011+ Green Book tabulates PSD directly (validated against field passing behavior via the Glennon and Hassan et al. abort/complete models); intermediate speeds interpolate linearly.

    PSD = Green Book Table 3-4 value at the design speed

    PSD = 1000 ft at 60 mi/h

    = 1000 ft

Results

Passing sight distance (design value)

1000ft

Assumed passing-vehicle speed (= design speed)

88ft/s

Assumed passed-vehicle speed

70.4ft/s

Where this answer was checked
source
AASHTO 2011 Green Book Table 3-4 via NCHRP 605 Exhibit 3-4 (fetched) and MDOT guidelines (fetched) — URLs in file header — table row: 60 mph | passed 48 | passing 60 | PSD 1,000 ft
verified by
published-answer
derivation
Tabulated design value (no closed form exists to re-derive); both fetched sources print the identical row. Passed-vehicle speed check: 60 − 12 = 48 mph.

Example 2

metric 100 km/h → PSD 320 m (passed vehicle assumed at 81 km/h)

Given

design speed
100 km/h

Assumptions

  • Model: AASHTO 2011+ single-model PSD design values (Green Book Table 3-4, adopted from NCHRP Report 605) — the Green Book publishes design values, not a closed-form equation; the obsolete pre-2001 four-component model is intentionally NOT used.
  • Model assumptions (Green Book): passing and opposing vehicles travel at the design speed; the passed vehicle is 19 km/h slower; both vehicles are 5.8 m long; 1 s perception-reaction to abort; aborts decelerate at 3.4 m/s²; 1-s headways and clearance.
  • Sight-distance measurement basis: driver eye height 3.5 ft (1.08 m) to an object height of 3.5 ft (the opposing vehicle).

Solution steps

  1. Assumed maneuver speeds

    The passing (and opposing) vehicle travels at the design speed; the passed vehicle is assumed slower by a fixed differential.

    Vpassed = V − ΔV, with ΔV = 12 mph (US) or 19 km/h (metric)

    V = 100 km/h; passed vehicle = 100 km/h − 19 km/h = 81 km/h

  2. Design PSD from the AASHTO table

    The 2011+ Green Book tabulates PSD directly (validated against field passing behavior via the Glennon and Hassan et al. abort/complete models); intermediate speeds interpolate linearly.

    PSD = Green Book Table 3-4 value at the design speed

    PSD = 320 m at 100 km/h

    = 320 m

Results

Passing sight distance (design value)

320m

Assumed passing-vehicle speed (= design speed)

27.78m/s

Assumed passed-vehicle speed

22.5m/s

Where this answer was checked
source
NCHRP 605 Exhibit 3-4, metric column (fetched) — URL in file header — table row: 100 km/h | passed 81 | passing 100 | PSD 320 m
verified by
published-answer
derivation
Tabulated design value. Passed-vehicle speed check: 100 − 19 = 81 km/h.

Example 3

US 50 mph → PSD 800 ft

Given

design speed
50 mi/h

Assumptions

  • Model: AASHTO 2011+ single-model PSD design values (Green Book Table 3-4, adopted from NCHRP Report 605) — the Green Book publishes design values, not a closed-form equation; the obsolete pre-2001 four-component model is intentionally NOT used.
  • Model assumptions (Green Book): passing and opposing vehicles travel at the design speed; the passed vehicle is 12 mph slower; both vehicles are 19 ft long; 1 s perception-reaction to abort; aborts decelerate at 11.2 ft/s²; 1-s headways and clearance.
  • Sight-distance measurement basis: driver eye height 3.5 ft (1.08 m) to an object height of 3.5 ft (the opposing vehicle).

Solution steps

  1. Assumed maneuver speeds

    The passing (and opposing) vehicle travels at the design speed; the passed vehicle is assumed slower by a fixed differential.

    Vpassed = V − ΔV, with ΔV = 12 mph (US) or 19 km/h (metric)

    V = 50 mi/h; passed vehicle = 50 mi/h − 12 mi/h = 38 mi/h

  2. Design PSD from the AASHTO table

    The 2011+ Green Book tabulates PSD directly (validated against field passing behavior via the Glennon and Hassan et al. abort/complete models); intermediate speeds interpolate linearly.

    PSD = Green Book Table 3-4 value at the design speed

    PSD = 800 ft at 50 mi/h

    = 800 ft

Results

Passing sight distance (design value)

800ft

Assumed passing-vehicle speed (= design speed)

73.33ft/s

Assumed passed-vehicle speed

55.73ft/s

Where this answer was checked
source
AASHTO 2011 Green Book Table 3-4 via NCHRP 605 / MDOT (both fetched) — URLs in file header — table row: 50 mph | passed 38 | passing 50 | PSD 800 ft
verified by
published-answer
derivation
Tabulated design value; both fetched sources agree.