3.1 Basic Freeway Segments & Multilane Highways (HCM 7th Edition)

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1 Introduction & PTOE Exam Overview

1.1 The PTOE Credential: Certification Overview & Industry Value 1.2 Core Industry Reference Standards in Traffic Operations 1.3 Study Guide Architecture, Blueprint Alignment & Exam-Day Strategy

2 Domain 1: Traffic Flow Theory & Fundamental Concepts

2.1 Macroscopic Traffic Stream Models & Fundamental Diagram (q = k × u) 2.2 Microscopic Traffic Characteristics & Car-Following Models 2.3 Hydrodynamic Shockwave Analysis & Traffic Queuing Models

3 Domain 1: Highway & Interrupted Flow Capacity Analysis (HCM)

3.1 Basic Freeway Segments & Multilane Highways (HCM 7th Edition) 3.2 Freeway Weaving, Merging, and Diverging Segments 3.3 Signalized Intersection Capacity & Delay Modeling (HCM)

4 Domain 1: Managed Lanes, Transit Priority, TSMO & Travel Demand Management

4.1 Unsignalized Intersections (TWSC, AWSC) & Modern Roundabouts Capacity 4.2 Managed Lanes, HOV/HOT Operations, & Ramp Metering 4.3 Transit Priority & Multimodal Signal Operations (TSP) 4.4 Transportation Systems Management and Operations (TSMO) & Regional ITS 4.5 Travel Demand Management (TDM) & Trip Reduction Strategies

5 Domain 2: Geometric Design Controls, Criteria, & Sight Distance

5.1 Functional Classification, Design Controls, & Context-Sensitive Design 5.2 Sight Distance Principles: Stopping, Decision, & Passing (AASHTO) 5.3 Horizontal Alignment, Curve Radius, & Superelevation Design

6 Domain 2: Roadway Cross-Sections & Access Management

6.1 Vertical Alignment: Tangent Grades, Crest & Sag Vertical Curves 6.2 Roadway Cross-Section Elements & AASHTO Clear Zone Concepts 6.3 Access Management Principles & Driveway Spacing Criteria

7 Domain 2: Intersection & Interchange Geometric Design

7.1 Intersection Channelization, Turn Lane Design, & Storage Length 7.2 Interchange Configurations & Operational Comparisons (Diamond, Cloverleaf, SPUI) 7.3 Diverging Diamond Interchanges (DDI / DCMI) Operational Principles 7.4 Modern Roundabout Geometric Design Elements & Fastest Paths 7.5 Multimodal Geometric Design: Pedestrian Facilities, Bikeways, & ADA

8 Domain 3: Traffic Safety Concepts, Human Factors, & Safe System

8.1 The Safe System Approach & Vision Zero Principles 8.2 Human Factors, Driver Expectancy, & Perception-Reaction Time (PRT) 8.3 Crash Collision Typologies & Statistical Rate Formulations (MEV, MVMT)

9 Domain 3: Highway Safety Manual (HSM) Predictive Methods & EB

9.1 Highway Safety Manual (HSM) Predictive Methodology & Part C Models 9.2 Safety Performance Functions (SPFs) & Crash Modification Factors (CMFs) 9.3 Empirical Bayes (EB) Method & Regression-to-the-Mean (RTM) Correction 9.4 Economic Appraisal of Safety Projects (Benefit-Cost Analysis, NPV)

10 Domain 3: Safety Countermeasures & Road Safety Audits (RSA)

10.1 Roadway Departure Countermeasures (Rumble Strips, Safety Edge, Barriers) 10.2 Intersection Safety Countermeasures (Sight Triangles, Left-Turn Calming, Roundabouts) 10.3 Vulnerable Road User (VRU) Safety Countermeasures (PHB/HAWK, RRFB, Curb Extensions) 10.4 Road Safety Audits (RSAs) & Systemic Safety Analysis

11 Domain 4: Traffic Signal Warrants & Isolated Timing (MUTCD/ITE)

11.1 MUTCD Traffic Signal Warrants (Warrants 1 through 9) 11.2 Signal Phasing Principles & NEMA Dual-Ring Operations 11.3 Clearance Intervals (ITE Kinematic Equations) & Pedestrian Timing Parameters

12 Domain 4: Signal Coordination, Networks, & ATSPMs

12.1 Actuated Signal Controller Parameters (Passage Time, Gap Reduction, Max Recall) 12.2 Traffic Signal Coordination: Bandwidth, Offsets, & Progression Models 12.3 Traffic Responsive & Adaptive Traffic Signal Control Systems (ASCS) 12.4 Automated Traffic Signal Performance Measures (ATSPMs) & High-Resolution Data

13 Domain 4: Signing, Markings, Work Zones, Grade Crossings & School Zones (MUTCD)

13.1 MUTCD Regulatory, Warning, & Guide Signs Principles and Placement 13.2 Sign Retroreflectivity Standards & Nighttime Visual Maintenance 13.3 Longitudinal Pavement Markings, Delineators, & Object Markers 13.4 Temporary Traffic Control (TTC) & Work Zone Safety (MUTCD Part 6) 13.5 Highway-Rail Grade Crossings: Warning Devices, Preemption & Storage 13.6 School Zone Traffic Control & Student Walk Route Planning

14 Domain 5: Traffic Studies & Applied Statistical Methods

14.1 Applied Statistical Distributions & Sample Size Determination 14.2 Spot Speed Studies, 85th Percentile Speed, & 10-mph Pace 14.3 Volume Count Methodologies & Expansion Factoring (ADT, AADT, PHF)

15 Domain 5: Traffic Impact Studies & Trip Generation (ITE)

15.1 Travel Time, Delay, & Intersection Queue Studies 15.2 Parking Supply, Duration, & Turnover Analysis 15.3 Traffic Impact Study (TIS) Scoping, Horizon Years, & Mitigation 15.4 ITE Trip Generation Handbook: Average Rates vs. Regression Equations

16 Domain 6: Environmental, Institutional, Ethics & Equity Issues

16.1 Vehicle Emissions, Air Quality Conformity, & Decarbonization 16.2 Traffic Noise Modeling (TNM) & Noise Abatement Criteria (NAC) 16.3 Long-Range Transportation Planning & the NEPA Environmental Review 16.4 Professional Engineering Ethics, Tort Liability, & Risk Management 16.5 Transportation Equity, Access & Multimodal Community Considerations

3.1 Basic Freeway Segments & Multilane Highways (HCM 7th Edition)

Key Takeaways Explain This Topic AI

Uninterrupted flow capacity analysis evaluates facilities free from external fixed interruptions like traffic signals or stop signs.

Free-Flow Speed (FFS) is calculated from base free-flow speed adjusted for lane width, right lateral clearance, total ramp density, and median/access point density on multilane highways.

Demand flow rate (v_p) converts hourly volumes to equivalent passenger cars per hour per lane during the peak 15 minutes using PHF, heavy vehicle adjustments (f_HV), and driver population factors (f_p).

The primary service measure for basic freeway segments and multilane highways is Density (D) in passenger cars per mile per lane (pc/mi/ln), with LOS E terminating at capacity (45 pc/mi/ln on freeways).

Last updated: August 2026

Basic Freeway Segments & Multilane Highways (HCM 7th Edition)

Uninterrupted flow facilities—principally freeways and multilane rural/suburban highways—have no fixed external causes of delay, such as traffic control signals, stop signs, or railroad grade crossings. Traffic flow characteristics result purely from interactions among vehicles, geometric constraints, environmental conditions, and driver behavior.

Under the Highway Capacity Manual (HCM 7th Edition) , operational evaluation focuses on establishing the Level of Service (LOS) by computing the traffic density ( D D D ) in equivalent passenger cars per mile per lane ( pc/mi/ln \text{pc/mi/ln} pc/mi/ln ).

Base (Ideal) Conditions for Uninterrupted Flow

HCM capacity models define base (ideal) operating conditions where geometric and operational parameters impose zero degradation on performance:

Lane width: Minimum 12 ft (3.6 m).

Right-side lateral clearance: Minimum 6 ft (1.8 m) between the edge of the travel lane and roadside obstructions or retaining walls.

Median lateral clearance: Minimum 2 ft (0.6 m) for divided freeways.

Traffic composition: 100% passenger cars ( 0 % 0\% 0% heavy vehicles: trucks, buses, RVs).

Terrain: Level terrain ( 0 % 0\% 0% longitudinal grade).

Driver population: Regular, familiar commuter drivers ( f p = 1.00 f_p = 1.00 f p ​ = 1.00 ).

Interchange spacing: Interchange density of 0.5 interchanges/mile (average 2-mile spacing).

Environmental / Lighting: Clear weather, dry pavement, and daylight conditions.

When actual field conditions diverge from these base parameters, specific empirical correction factors reduce estimated free-flow speed and adjust volume demands upward.

Free-Flow Speed (FFS) Determination

Free-flow speed is the mean speed of passenger cars measured under low-to-moderate volume conditions ( v p ≤ 1 , 000 pc/h/ln v_p \le 1,000\text{ pc/h/ln} v p ​ ≤ 1 , 000 pc/h/ln ) where drivers are unrestrained by upstream or downstream congestion.

1. Basic Freeway Segments

If field measurements of speed are unavailable, FFS is estimated using the HCM regression formula: F F S = 75.4 − f L W − f R L C − 3.22 × T R D 0.84 FFS = 75.4 - f_{LW} - f_{RLC} - 3.22 \times TRD^{0.84} FFS = 75.4 − f L W ​ − f R L C ​ − 3.22 × TR D 0.84

Where:

F F S FFS FFS = estimated free-flow speed (mph).

f L W f_{LW} f L W ​ = adjustment for lane width (mph; 0.0 mph 0.0\text{ mph} 0.0 mph for ≥ 12 ft \ge 12\text{ ft} ≥ 12 ft , 1.9 mph 1.9\text{ mph} 1.9 mph for 11 ft 11\text{ ft} 11 ft , 6.6 mph 6.6\text{ mph} 6.6 mph for 10 ft 10\text{ ft} 10 ft ).

f R L C f_{RLC} f R L C ​ = adjustment for right-shoulder lateral clearance (mph; depends on number of directional lanes N N N and clear shoulder width; 0.0 mph 0.0\text{ mph} 0.0 mph for ≥ 6 ft \ge 6\text{ ft} ≥ 6 ft ).

T R D TRD TR D = Total Ramp Density (ramps/mile), calculated as total on-ramps and off-ramps within a 6-mile segment (3 miles upstream and 3 miles downstream of the midpoint of the study section) divided by 6.0 miles.

2. Multilane Highways

For multilane highways (which may feature at-grade intersections, driveways, or traffic signals spaced > 2.0 miles > 2.0\text{ miles} > 2.0 miles apart), FFS is computed from a Base Free-Flow Speed ( B F F S BFFS BFFS , typically 60 mph): F F S = B F F S − f L W − f T L C − f M − f A FFS = BFFS - f_{LW} - f_{TLC} - f_M - f_A FFS = BFFS − f L W ​ − f T L C ​ − f M ​ − f A ​

Where:

f T L C f_{TLC} f T L C ​ = adjustment for total lateral clearance (sum of right shoulder clearance and left/median clearance, up to 12 ft maximum).

f M f_M f M ​ = adjustment for median type ( 0.0 mph 0.0\text{ mph} 0.0 mph for divided highways with physical barrier or raised median; 1.6 mph 1.6\text{ mph} 1.6 mph for undivided highways; 0.0 mph 0.0\text{ mph} 0.0 mph for two-way left-turn lanes [TWLTL]).

f A f_A f A ​ = adjustment for access point density (driveways and minor unsignalized access per mile): f A = 0.25 × A P D f_A = 0.25 \times APD f A ​ = 0.25 × A P D

Where A P D APD A P D is the total number of active access points per mile on the study side of the roadway.

Loading diagram... HCM Basic Freeway Capacity & Level of Service Analysis Flowchart

Demand Flow Rate Adjustment ( v p v_p v p ​ )

Raw hourly traffic counts ( V V V , veh/h) must be converted into a peak 15-minute equivalent passenger-car flow rate per lane under base conditions ( v p v_p v p ​ , pc/h/ln): v p = V P H F × N × f H V × f p v_p = \frac{V}{PHF \times N \times f_{HV} \times f_p} v p ​ = P H F × N × f H V ​ × f p ​ V ​

Where:

V V V = peak-hour directional volume (veh/h).

P H F PHF P H F = Peak Hour Factor = V 4 × V 15 = \frac{V}{4 \times V_{15}} = 4 × V 15 ​ V ​ , where V 15 V_{15} V 15 ​ is the maximum volume during a single 15-minute interval within the peak hour.

N N N = number of travel lanes in the specified direction of travel.

f p f_p f p ​ = driver population adjustment factor ( 1.00 1.00 1.00 for typical urban commuter streams; 0.85 − 0.97 0.85 - 0.97 0.85 − 0.97 for predominantly unfamiliar or recreational weekend traffic).

f H V f_{HV} f H V ​ = heavy-vehicle adjustment factor.

Heavy Vehicle Adjustment Factor ( f H V f_{HV} f H V ​ )

Heavy vehicles occupy more physical space and exhibit inferior acceleration/deceleration performance compared to passenger cars. The adjustment factor is: f H V = 1 1 + P T ( E T − 1 ) + P R ( E R − 1 ) f_{HV} = \frac{1}{1 + P_T(E_T - 1) + P_R(E_R - 1)} f H V ​ = 1 + P T ​ ( E T ​ − 1 ) + P R ​ ( E R ​ − 1 ) 1 ​

Where:

P T , P R P_T, P_R P T ​ , P R ​ = proportion of trucks/buses and recreational vehicles (RVs) in the traffic stream, expressed as decimals.

E T , E R E_T, E_R E T ​ , E R ​ = passenger car equivalents for trucks/buses and RVs for the given terrain profile.

• Terrain Type Truck/Bus Equivalent ( E T E_T E T ​ ) RV Equivalent ( E R E_R E R ​ )
• Level Terrain (grades < 2 % < 2\% < 2% of any length) 2.0 2.0 2.0 1.2 1.2 1.2
• Rolling Terrain (moderate grades causing trucks to slow down without crawling) 3.0 3.0 3.0 1.5 1.5 1.5
• Mountainous Terrain (steep sustained grades forcing heavy trucks to crawl speed) 4.5 4.5 4.5 1.8 1.8 1.8

Note for Specific Grades: For extended steep grades ( > 3 % > 3\% > 3% grade over > 0.5 miles > 0.5\text{ miles} > 0.5 miles ), the HCM provides specific E T E_T E T ​ lookup tables categorized by percent grade, length of grade, and truck weight-to-power ratio.

• Speed-Flow Curves, Density, and Level of Service Thresholds
• Speed-Flow Relationship & Breakpoint

Under HCM 7th Edition formulations, vehicle operating speed remains constant at the Free-Flow Speed ( F F S FFS FFS ) up to a breakpoint demand ( B P BP BP ) : B P = 1000 + 40 × ( 75 − F F S ) [ for 55 ≤ F F S ≤ 75 mph ] BP = 1000 + 40 \times (75 - FFS) \quad [\text{for } 55 \le FFS \le 75\text{ mph}] BP = 1000 + 40 × ( 75 − FFS ) [ for 55 ≤ FFS ≤ 75 mph ]

For F F S = 75 mph FFS = 75\text{ mph} FFS = 75 mph , B P = 1 , 000 pc/h/ln BP = 1,000\text{ pc/h/ln} BP = 1 , 000 pc/h/ln .

For F F S = 70 mph FFS = 70\text{ mph} FFS = 70 mph , B P = 1 , 200 pc/h/ln BP = 1,200\text{ pc/h/ln} BP = 1 , 200 pc/h/ln .

For F F S = 65 mph FFS = 65\text{ mph} FFS = 65 mph , B P = 1 , 400 pc/h/ln BP = 1,400\text{ pc/h/ln} BP = 1 , 400 pc/h/ln .

For F F S = 55 mph FFS = 55\text{ mph} FFS = 55 mph , B P = 1 , 800 pc/h/ln BP = 1,800\text{ pc/h/ln} BP = 1 , 800 pc/h/ln .

When v p ≤ B P v_p \le BP v p ​ ≤ BP , the space mean speed S = F F S S = FFS S = FFS . When B P < v p ≤ C BP < v_p \le C BP < v p ​ ≤ C , speed decreases non-linearly toward capacity ( C C C ). At capacity ( v p = C v_p = C v p ​ = C ), the density reaches exactly 45.0 pc/mi/ln 45.0\text{ pc/mi/ln} 45.0 pc/mi/ln for all freeway free-flow speed curves.

Directional Lane Capacities

F F S = 75 mph ⟹ C = 2 , 400 pc/h/ln FFS = 75\text{ mph} \implies C = 2,400\text{ pc/h/ln} FFS = 75 mph ⟹ C = 2 , 400 pc/h/ln

F F S = 70 mph ⟹ C = 2 , 400 pc/h/ln FFS = 70\text{ mph} \implies C = 2,400\text{ pc/h/ln} FFS = 70 mph ⟹ C = 2 , 400 pc/h/ln

F F S = 65 mph ⟹ C = 2 , 350 pc/h/ln FFS = 65\text{ mph} \implies C = 2,350\text{ pc/h/ln} FFS = 65 mph ⟹ C = 2 , 350 pc/h/ln

F F S = 60 mph ⟹ C = 2 , 300 pc/h/ln FFS = 60\text{ mph} \implies C = 2,300\text{ pc/h/ln} FFS = 60 mph ⟹ C = 2 , 300 pc/h/ln

F F S = 55 mph ⟹ C = 2 , 250 pc/h/ln FFS = 55\text{ mph} \implies C = 2,250\text{ pc/h/ln} FFS = 55 mph ⟹ C = 2 , 250 pc/h/ln

Density Calculation

Density ( D D D ) defines the degree of proximity between vehicles and serves as the primary operational measure of effectiveness: D = v p S ( pc/mi/ln ) D = \frac{v_p}{S} \quad (\text{pc/mi/ln}) D = S v p ​ ​ ( pc/mi/ln )

Level of Service (LOS) Criteria (HCM 7th Edition)

Level of Service Basic Freeway Density ( D D D , pc/mi/ln) Multilane Highway Density ( D D D , pc/mi/ln) Operational Characteristics

LOS A ≤ 11.0 \le 11.0 ≤ 11.0 ≤ 11.0 \le 11.0 ≤ 11.0 Free flow; complete maneuverability and lane-selection freedom.

LOS B > 11.0 to 18.0 > 11.0 \text{ to } 18.0 > 11.0 to 18.0 > 11.0 to 18.0 > 11.0 \text{ to } 18.0 > 11.0 to 18.0 Stable flow; slight decline in freedom to maneuver within stream.

LOS C > 18.0 to 26.0 > 18.0 \text{ to } 26.0 > 18.0 to 26.0 > 18.0 to 26.0 > 18.0 \text{ to } 26.0 > 18.0 to 26.0 Stable flow; lane changes require driver vigilance and spacing selection.

LOS D > 26.0 to 35.0 > 26.0 \text{ to } 35.0 > 26.0 to 35.0 > 26.0 to 35.0 > 26.0 \text{ to } 35.0 > 26.0 to 35.0 Approaching unstable flow; minor incidents generate immediate shockwaves.

LOS E > 35.0 to 45.0 > 35.0 \text{ to } 45.0 > 35.0 to 45.0 > 35.0 to 40.0 – 45.0 > 35.0 \text{ to } 40.0\text{–}45.0 > 35.0 to 40.0 – 45.0 Operating at capacity; volatile flow with near-zero buffer spacing.

LOS F > 45.0 > 45.0 > 45.0 or v / c > 1.00 v/c > 1.00 v / c > 1.00 > 40.0 – 45.0 > 40.0\text{–}45.0 > 40.0 – 45.0 or v / c > 1.00 v/c > 1.00 v / c > 1.00 Breakdown / forced flow; upstream queuing and severe stop-and-go delays.

• Step-by-Step Worked Engineering Example
• Problem Statement

A suburban 6-lane freeway (3 lanes in each direction, N = 3 N=3 N = 3 ) carries a directional peak-hour volume of V = 4 , 860 veh/h V = 4,860\text{ veh/h} V = 4 , 860 veh/h . Field survey data indicates:

• Peak Hour Factor ( P H F PHF P H F ) = 0.90 0.90 0.90
• Traffic composition: 8 % 8\% 8% heavy trucks ( P T = 0.08 P_T = 0.08 P T ​ = 0.08 ), 0 % 0\% 0% RVs
• Terrain: Rolling terrain ( E T = 3.0 E_T = 3.0 E T ​ = 3.0 )
• Driver population: Daily commuters ( f p = 1.00 f_p = 1.00 f p ​ = 1.00 )

Geometric attributes: 12-ft lanes, 6-ft right shoulder, T R D = 1.5 ramps/mile TRD = 1.5\text{ ramps/mile} TR D = 1.5 ramps/mile

Step 1: Determine Free-Flow Speed ( F F S FFS FFS ) F F S = 75.4 − f L W − f R L C − 3.22 × T R D 0.84 FFS = 75.4 - f_{LW} - f_{RLC} - 3.22 \times TRD^{0.84} FFS = 75.4 − f L W ​ − f R L C ​ − 3.22 × TR D 0.84

Since lanes are 12 ft ( f L W = 0.0 f_{LW} = 0.0 f L W ​ = 0.0 ) and right shoulder is 6 ft ( f R L C = 0.0 f_{RLC} = 0.0 f R L C ​ = 0.0 ): F F S = 75.4 − 0.0 − 0.0 − 3.22 × ( 1.5 ) 0.84 = 75.4 − 3.22 × 1.405 = 75.4 − 4.52 = 70.88 ≈ 70.9 mph FFS = 75.4 - 0.0 - 0.0 - 3.22 \times (1.5)^{0.84} = 75.4 - 3.22 \times 1.405 = 75.4 - 4.52 = 70.88 \approx 70.9\text{ mph} FFS = 75.4 − 0.0 − 0.0 − 3.22 × ( 1.5 ) 0.84 = 75.4 − 3.22 × 1.405 = 75.4 − 4.52 = 70.88 ≈ 70.9 mph

Step 2: Compute Heavy Vehicle Factor ( f H V f_{HV} f H V ​ ) f H V = 1 1 + 0.08 ( 3.0 − 1 ) = 1 1 + 0.16 = 1 1.16 = 0.8621 f_{HV} = \frac{1}{1 + 0.08(3.0 - 1)} = \frac{1}{1 + 0.16} = \frac{1}{1.16} = 0.8621 f H V ​ = 1 + 0.08 ( 3.0 − 1 ) 1 ​ = 1 + 0.16 1 ​ = 1.16 1 ​ = 0.8621

Step 3: Calculate Peak 15-min Demand Flow Rate ( v p v_p v p ​ ) v p = 4 , 860 0.90 × 3 × 0.8621 × 1.00 = 4 , 860 2.3277 = 2 , 088 pc/h/ln v_p = \frac{4,860}{0.90 \times 3 \times 0.8621 \times 1.00} = \frac{4,860}{2.3277} = 2,088\text{ pc/h/ln} v p ​ = 0.90 × 3 × 0.8621 × 1.00 4 , 860 ​ = 2.3277 4 , 860 ​ = 2 , 088 pc/h/ln

Step 4: Check Breakpoint and Determine Speed ( S S S )

For F F S ≈ 70.9 mph FFS \approx 70.9\text{ mph} FFS ≈ 70.9 mph , the breakpoint is: B P = 1000 + 40 × ( 75 − 70.88 ) = 1000 + 40 × 4.12 = 1 , 165 pc/h/ln BP = 1000 + 40 \times (75 - 70.88) = 1000 + 40 \times 4.12 = 1,165\text{ pc/h/ln} BP = 1000 + 40 × ( 75 − 70.88 ) = 1000 + 40 × 4.12 = 1 , 165 pc/h/ln

Since v p = 2 , 088 > 1 , 165 pc/h/ln v_p = 2,088 > 1,165\text{ pc/h/ln} v p ​ = 2 , 088 > 1 , 165 pc/h/ln , speed is slightly reduced below FFS. Evaluating along the 70 mph curve gives space mean speed S ≈ 68.2 mph S \approx 68.2\text{ mph} S ≈ 68.2 mph .

Step 5: Compute Density ( D D D ) and Level of Service D = v p S = 2 , 088 68.2 = 30.6 pc/mi/ln D = \frac{v_p}{S} = \frac{2,088}{68.2} = 30.6\text{ pc/mi/ln} D = S v p ​ ​ = 68.2 2 , 088 ​ = 30.6 pc/mi/ln

Comparing against HCM Level of Service density thresholds:

26.0 < D ≤ 35.0 pc/mi/ln ⟹ 26.0 < D \le 35.0\text{ pc/mi/ln} \implies 26.0 < D ≤ 35.0 pc/mi/ln ⟹ Level of Service D (LOS D).