CELE Transportation & Highway Engineering — Traffic Engineering and Highway CapacityConcept Map

Concept

Fundamental Traffic Variables

Sub Concepts

• Flow (Volume) q
• Speed u (space-mean)
• Density (Concentration) k

Relationship To Central

Core inputs to flow modelling; define the state of traffic at any instant

Concept

Fundamental Flow Equation

Sub Concepts

• q = k·u relationship
• Flow-density curve
• Optimal density concept
• Congested vs free-flow regimes

Relationship To Central

Mathematical relationship linking traffic variables; basis for capacity estimation

Concept

Spacing and Headway Analysis

Sub Concepts

• Spacing s = 1000/k (metres)
• Headway h = 3600/q (seconds)
• Inverse relationship to density
• Safety and comfort implications

Relationship To Central

Physical and temporal measures of vehicle separation; indicators of traffic state

Concept

Peak-Hour Factor (PHF)

Sub Concepts

• PHF = V / (4·V₁₅) formula
• Design flow rate = V / PHF
• Peak 15-minute concentration
• Range 0.25 to 1.0

Relationship To Central

Converts hourly count to design flow; accounts for temporal demand variation

Concept

Capacity and Highway Performance

Sub Concepts

• Capacity definition (~2000 pc/h/lane ideal)
• Ideal vs field conditions
• Lane width, grade, weather effects
• Heavy vehicle equivalents

Relationship To Central

Determines maximum sustainable flow; defines facility adequacy

Concept

Level of Service (LOS) Classification

Sub Concepts

• LOS A (free flow) to F (breakdown)
• Freeways: graded by density
• Intersections: graded by delay
• v/c ratio thresholds
• Design LOS criteria by road class

Relationship To Central

Qualitative measure of operating conditions; basis for design standards

Concept

Signal Timing and Intersection Control

Sub Concepts

• Webster's cycle length formula
• Optimal cycle length
• Delay estimation (Webster/HCM)
• Phase split design

Relationship To Central

Manages capacity at controlled intersections; optimizes green time allocation

Concept

Road Classification and Design Standards

Sub Concepts

• National roads (DPWH/RA 544 jurisdiction)
• Provincial and municipal roads
• Expressways and tollways
• Design speed and functional class links

Relationship To Central

Establishes context for capacity and LOS targets per Philippine standards

To

Fundamental Flow Equation q = k·u

From

Flow (Volume) q

Strength

strong

Relationship

Primary input variable; forms left side of fundamental relationship

To

Fundamental Flow Equation q = k·u

From

Speed u (space-mean)

Strength

strong

Relationship

Essential variable; must use space-mean (harmonic mean) not time-mean for accuracy

To

Fundamental Flow Equation q = k·u

From

Density (Concentration) k

Strength

strong

Relationship

Core variable; determines vehicle spacing and congestion state

To

Density (Concentration) k

From

Spacing s = 1000/k

Strength

strong

Relationship

Inverse relationship; as density increases, spacing decreases

To

Flow (Volume) q

From

Headway h = 3600/q

Strength

strong

Relationship

Inverse relationship; as flow increases, headway (time gap) decreases

To

Capacity Concepts

From

Flow-Density Curve

Strength

strong

Relationship

Graphical representation showing peak capacity occurs at intermediate density

To

Level of Service (LOS) Classification

From

Capacity Concepts

Strength

strong

Relationship

Capacity sets upper threshold; LOS grades service quality relative to capacity

To

Design flow rate

From

Peak-Hour Factor (PHF)

Strength

strong

Relationship

PHF converts hourly volume to design flow; accounts for peak concentration

To

Capacity Concepts

From

Design flow rate

Strength

strong

Relationship

Design flow compared to capacity determines if facility is adequate

To

Road Classification and Design Standards

From

Level of Service (LOS) Classification

Strength

strong

Relationship

Different road classes assigned different target LOS values per RA 544 and DPWH standards

To

Level of Service (LOS) Classification

From

Signal Timing and Intersection Control

Strength

moderate

Relationship

Intersection LOS determined by control delay; signal timing reduces delay and improves LOS

To

Capacity Concepts

From

Capacity Adjustment Factors

Strength

strong

Relationship

Reduce ideal 2000 pc/h/lane to realistic field capacity via lane width, grade, vehicle mix, weather

To

Level of Service (LOS) Classification

From

Density (Concentration) k

Strength

strong

Relationship

Freeway LOS determined directly by density; threshold values define each LOS grade

To

Signal Timing and Intersection Control

From

Webster's Cycle Length Formula

Strength

strong

Relationship

Calculates optimal cycle length to minimize delay and maximize intersection capacity

To

Speed-Density Curve

From

Flow-Density Curve

Strength

moderate

Relationship

Both derived from same data; show complementary relationships among traffic variables

To

Capacity Adjustment Factors

From

Vehicle Composition

Strength

strong

Relationship

Heavy vehicles reduce effective capacity; converted to passenger car unit equivalents

To

Peak-Hour Factor (PHF)

From

Peak 15-Minute Count V₁₅

Strength

strong

Relationship

V₁₅ is divisor in PHF formula; measures peak demand concentration within hour

To

Capacity Adjustment Factors

From

Ideal vs Field Conditions

Strength

strong

Relationship

Field conditions require adjustment factors; ideal 2000 pc/h/lane is baseline

To

Capacity Concepts

From

Road Classification and Design Standards

Strength

moderate

Relationship

Road class determines design speed and capacity target; higher class = higher capacity requirement

To

Flow-Density Curve

From

Fundamental Flow Equation q = k·u

Strength

strong

Relationship

Mathematical basis for curve; shows how flow varies with density at different speeds