CELE Transportation & Highway Engineering — Highway Engineering and Geometric DesignConcept Map

Concept

Stopping Sight Distance (SSD)

Sub Concepts

• Perception-reaction distance (0.278Vt)
• Braking distance (V²/[254(f±G)])
• Grade effect (uphill vs. downhill)
• Friction coefficient (f)
• Reaction time (t ≈ 2.5 s)

Relationship To Central

Core safety requirement determining safe braking space

Concept

Horizontal Alignment & Superelevation

Sub Concepts

• Minimum radius formula: Rmin = V²/[127(e+f)]
• Superelevation angle (e)
• Side friction (f)
• Design speed (V)
• Transition (spiral) curves
• Superelevation runoff

Relationship To Central

Controls curve safety and centripetal force balance

Concept

Vertical Alignment

Sub Concepts

• Parabolic curves (crest & sag)
• Grade limitations
• Crest curve sight distance
• Sag curve headlight throw
• Vehicle performance on grades

Relationship To Central

Manages grades, drainage, and sight over crests/sags

Concept

Cross-Section Design

Sub Concepts

• Lane widths (standard & design vehicle)
• Shoulder width and type
• Camber/crown for drainage
• Median design
• Clear zone width
• Traffic barriers and safety

Relationship To Central

Defines lane widths, shoulders, drainage, and clear zones

Concept

Design Parameters & Standards

Sub Concepts

• Design speed (km/h)
• Design vehicle (car, truck, bus)
• Traffic volume (AADT)
• Friction coefficients
• Grade limits
• Philippine standards (DPWH, NSCP)

Relationship To Central

Foundational inputs for all geometric calculations

Concept

Safety & Operational Considerations

Sub Concepts

• Passing sight distance
• Decision sight distance
• Night visibility
• Vehicle stability on curves
• Skid resistance
• Drainage slope

Relationship To Central

Ensures geometry accommodates human and vehicle limits

To

Design Speed

From

Stopping Sight Distance (SSD)

Strength

strong

Relationship

SSD is calculated directly from design speed V; higher speed → longer SSD required

To

Vertical Alignment

From

Stopping Sight Distance (SSD)

Strength

strong

Relationship

SSD limits crest curve length; inadequate sight over crests violates SSD standards

To

Grade Effect

From

Stopping Sight Distance (SSD)

Strength

strong

Relationship

Grade sign directly modifies braking distance denominator; downgrade lengthens SSD, upgrade shortens it

To

Design Speed

From

Horizontal Alignment & Superelevation

Strength

strong

Relationship

Minimum radius Rmin = V²/[127(e+f)] is quadratic in speed; faster speeds require much sharper curves or larger radii

To

Superelevation Runoff

From

Horizontal Alignment & Superelevation

Strength

strong

Relationship

Transition spirals develop superelevation gradually over runoff distance; longer spirals reduce rate of change (comfort)

To

Friction Coefficient

From

Horizontal Alignment & Superelevation

Strength

strong

Relationship

Side friction (f) complements superelevation (e) in providing centripetal force; both contribute to Rmin formula

To

Design Speed

From

Vertical Alignment

Strength

strong

Relationship

Design speed determines sight distance threshold; higher speeds require longer vertical curves

To

Grade Limitations

From

Vertical Alignment

Strength

moderate

Relationship

Steep grades (>6%) may trigger climbing lanes, runaway truck ramps, or design speed reduction

To

Design Vehicle

From

Cross-Section Design

Strength

strong

Relationship

Design vehicle width and turning radius determine minimum lane width and shoulder width

To

Drainage

From

Cross-Section Design

Strength

moderate

Relationship

Crown (camber) slope must match cross-fall percentage (2–3%) to shed water; affects lane edge profile

To

All Geometric Elements

From

Design Parameters & Standards

Strength

strong

Relationship

Design speed, friction coefficient, and vehicle type are inputs to SSD, Rmin, grade limits, and cross-section

To

Stopping Sight Distance (SSD)

From

Friction Coefficient

Strength

strong

Relationship

Friction (f) in denominator of braking distance formula; higher f → shorter SSD

To

Minimum Radius

From

Friction Coefficient

Strength

strong

Relationship

Side friction (f) in Rmin formula adds to superelevation (e); higher f → smaller Rmin

To

Vehicle Performance

From

Grade Effect

Strength

moderate

Relationship

Downgrade increases braking distance and brake fade risk; upgrade aids deceleration but limits engine braking

To

Design Speed

From

Clear Zone Width

Strength

moderate

Relationship

Higher speeds increase clear zone requirement to safely recover from edge departures

To

Minimum Radius

From

Superelevation Angle

Strength

strong

Relationship

Larger superelevation (e) reduces Rmin; maximum e is typically 4–8% to prevent sliding on wet pavements

To

Stopping Sight Distance (SSD)

From

Reaction Time

Strength

strong

Relationship

Reaction time (t ≈ 2.5 s) multiplies design speed in perception-reaction distance term (0.278Vt)

To

Vertical Alignment

From

Passing Sight Distance

Strength

moderate

Relationship

On undivided highways, crest curve length must accommodate passing sight distance (longer than stopping sight)

To

Clear Zone Width

From

Shoulder Width

Strength

moderate

Relationship

Paved shoulder width contributes to clear zone; wider shoulders reduce clear zone barrier distance

To

Design Vehicle

From

Lane Width

Strength

strong

Relationship

Design vehicle width plus lateral clearance (0.2 m per side) determines minimum lane width (typically 3.5–3.75 m)