Look up and interpolate AASHTO 2011+ passing sight distances for two-lane highways. See the assumed passing and passed vehicle speeds.
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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
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)
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
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
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
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
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)
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.