Traffic Engineering and Highway Capacity - Concept Map
Fundamental Traffic Flow Relationship and Highway Capacity Analysis
Related concepts
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
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
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
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
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
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
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
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
Concept connections
- Flow (Volume) qFundamental Flow Equation q = k·uPrimary input variable; forms left side of fundamental relationship
- Speed u (space-mean)Fundamental Flow Equation q = k·uEssential variable; must use space-mean (harmonic mean) not time-mean for accuracy
- Density (Concentration) kFundamental Flow Equation q = k·uCore variable; determines vehicle spacing and congestion state
- Spacing s = 1000/kDensity (Concentration) kInverse relationship; as density increases, spacing decreases
- Headway h = 3600/qFlow (Volume) qInverse relationship; as flow increases, headway (time gap) decreases
- Flow-Density CurveCapacity ConceptsGraphical representation showing peak capacity occurs at intermediate density
- Capacity ConceptsLevel of Service (LOS) ClassificationCapacity sets upper threshold; LOS grades service quality relative to capacity
- Peak-Hour Factor (PHF)Design flow ratePHF converts hourly volume to design flow; accounts for peak concentration
- Design flow rateCapacity ConceptsDesign flow compared to capacity determines if facility is adequate
- Level of Service (LOS) ClassificationRoad Classification and Design StandardsDifferent road classes assigned different target LOS values per RA 544 and DPWH standards
- Signal Timing and Intersection ControlLevel of Service (LOS) ClassificationIntersection LOS determined by control delay; signal timing reduces delay and improves LOS
- Capacity Adjustment FactorsCapacity ConceptsReduce ideal 2000 pc/h/lane to realistic field capacity via lane width, grade, vehicle mix, weather
- Density (Concentration) kLevel of Service (LOS) ClassificationFreeway LOS determined directly by density; threshold values define each LOS grade
- Webster's Cycle Length FormulaSignal Timing and Intersection ControlCalculates optimal cycle length to minimize delay and maximize intersection capacity
- Flow-Density CurveSpeed-Density CurveBoth derived from same data; show complementary relationships among traffic variables
- Vehicle CompositionCapacity Adjustment FactorsHeavy vehicles reduce effective capacity; converted to passenger car unit equivalents
- Peak 15-Minute Count V₁₅Peak-Hour Factor (PHF)V₁₅ is divisor in PHF formula; measures peak demand concentration within hour
- Ideal vs Field ConditionsCapacity Adjustment FactorsField conditions require adjustment factors; ideal 2000 pc/h/lane is baseline
- Road Classification and Design StandardsCapacity ConceptsRoad class determines design speed and capacity target; higher class = higher capacity requirement
- Fundamental Flow Equation q = k·uFlow-Density CurveMathematical basis for curve; shows how flow varies with density at different speeds
Diagrams
Traffic Engineering and Highway Capacity — Full Concept Hierarchy
Comprehensive mind map showing the hierarchical structure of traffic engineering concepts, from fundamental variables through capacity analysis and design application. Organizes all key topics and their relationships for comprehensive study.
Problem-Solving Flowchart: Determining Flow, Speed, and Density
Decision tree for solving fundamental traffic variable problems. Guides engineers through problem identification and equation selection, ensuring correct approach based on given data.
Peak-Hour Factor (PHF) and Design Flow Rate Calculation Process
Step-by-step procedure for calculating peak-hour factor from field counts and deriving the design flow rate. Shows validation checks and application to capacity decisions.
Level of Service (LOS) Determination for Freeways
Classification flowchart for determining freeway level of service based on density measurements. Shows threshold values and corresponding LOS grades from A through F.
Capacity Adjustment Factors and Effective Capacity Calculation
Systematic approach for adjusting ideal capacity to realistic field conditions. Shows how multiple factors (lane width, grade, vehicle mix, weather) reduce theoretical capacity.
Traffic Flow State Transitions and Congestion Lifecycle
State diagram showing how traffic transitions between free-flow and congested conditions throughout the day. Illustrates the lifecycle of congestion and recovery phases.
Typical Distribution of Level of Service (LOS) Requirements in Highway Design
Pie chart showing typical level-of-service targets assigned to different road classes in Philippines highway design. Reflects design standards and functional classification hierarchy.