3.3 Signalized Intersection Capacity & Delay Modeling (HCM)

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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

3.3 Signalized Intersection Capacity & Delay Modeling (HCM)

Key Takeaways Explain This Topic AI

Signalized intersection capacity is determined at the lane-group level using adjusted saturation flow rates (s) and effective green ratios (g/C).

The base saturation flow rate (s_0 = 1,900 pc/h/ln) is modified by 11 adjustment factors accounting for lane width, grade, heavy vehicles, parking, buses, area type, lane utilization, and turning maneuvers.

HCM control delay consists of uniform delay (d_1), incremental delay for random arrivals and oversaturation (d_2), and initial queue delay (d_3).

Signalized Level of Service is determined strictly by average control delay, with LOS F defined by delay > 80.0 s/veh or a volume-to-capacity ratio X > 1.00.

Last updated: August 2026

Signalized Intersection Capacity & Delay Modeling (HCM)

Signalized intersections represent the primary form of interrupted flow in urban traffic systems. Capacity and Level of Service are evaluated on a lane group basis—grouping lanes with shared vehicular movements (e.g., exclusive left-turn lane, exclusive right-turn lane, or combined through-and-right lanes).

Base Saturation Flow Rate ( s 0 s_0 s 0 ​ ) and Adjustment Factors

The saturation flow rate ( s s s ) represents the maximum equivalent hourly rate at which vehicles can pass through a signalized lane group during continuous green signal indication, assuming a constant queue of vehicles.

Standard Base Saturation Flow Rate: s 0 = 1 , 900 pc/h/ln s_0 = 1,900\text{ pc/h/ln} s 0 ​ = 1 , 900 pc/h/ln (passenger cars per hour of green per lane under ideal conditions).

Full 11-Factor HCM Saturation Flow Formula s = s 0 × N × f w × f H V × f g × f p × f b b × f a × f L U × f L T × f R T × f L p b × f R p b s = s_0 \times N \times f_w \times f_{HV} \times f_g \times f_p \times f_{bb} \times f_a \times f_{LU} \times f_{LT} \times f_{RT} \times f_{Lpb} \times f_{Rpb} s = s 0 ​ × N × f w ​ × f H V ​ × f g ​ × f p ​ × f bb ​ × f a ​ × f LU ​ × f L T ​ × f RT ​ × f L p b ​ × f Rp b ​

Where:

N N N = number of lanes in the lane group.

f w f_w f w ​ = Lane width adjustment factor: f w = 1 + W − 12 30 [ for lane width W ≥ 8.0 ft ] f_w = 1 + \frac{W - 12}{30} \quad [\text{for lane width } W \ge 8.0\text{ ft}] f w ​ = 1 + 30 W − 12 ​ [ for lane width W ≥ 8.0 ft ] (For standard 12-ft lanes, f w = 1.00 f_w = 1.00 f w ​ = 1.00 ; for 10-ft lanes, f w = 0.933 f_w = 0.933 f w ​ = 0.933 ; for 14-ft lanes, f w = 1.067 f_w = 1.067 f w ​ = 1.067 ) .

f H V f_{HV} f H V ​ = Heavy-vehicle adjustment factor: f H V = 100 100 + % H V ( E T − 1 ) = 1 1 + P H V ( E T − 1 ) f_{HV} = \frac{100}{100 + \%HV(E_T - 1)} = \frac{1}{1 + P_{HV}(E_T - 1)} f H V ​ = 100 + % H V ( E T ​ − 1 ) 100 ​ = 1 + P H V ​ ( E T ​ − 1 ) 1 ​ (Using E T = 2.0 passenger car equivalents E_T = 2.0\text{ passenger car equivalents} E T ​ = 2.0 passenger car equivalents per heavy vehicle) .

f g f_g f g ​ = Approach grade adjustment factor: f g = 1 − % G 200 f_g = 1 - \frac{\%G}{200} f g ​ = 1 − 200 % G ​ (Where % G \%G % G is approach grade; + 4 % uphill ⟹ f g = 0.98 +4\%\text{ uphill} \implies f_g = 0.98 + 4% uphill ⟹ f g ​ = 0.98 ; − 4 % downhill ⟹ f g = 1.02 -4\%\text{ downhill} \implies f_g = 1.02 − 4% downhill ⟹ f g ​ = 1.02 ) .

f p f_p f p ​ = On-street parking adjustment factor: f p = N − 0.1 − 18 N m 3 , 600 N f_p = \frac{N - 0.1 - \frac{18 N_m}{3,600}}{N} f p ​ = N N − 0.1 − 3 , 600 18 N m ​ ​ ​ ( N m N_m N m ​ = number of parking maneuvers per hour; with no parking, f p = 1.00 f_p = 1.00 f p ​ = 1.00 ) .

f b b f_{bb} f bb ​ = Bus blockage adjustment factor: f b b = N − 14.4 N B 3 , 600 N f_{bb} = \frac{N - \frac{14.4 N_B}{3,600}}{N} f bb ​ = N N − 3 , 600 14.4 N B ​ ​ ​ ( N B N_B N B ​ = number of local transit buses stopping within 250 ft of the stop line per hour) .

f a f_a f a ​ = Area type adjustment factor: 0.90 0.90 0.90 for Central Business Districts (CBD); 1.00 1.00 1.00 for all other non-CBD areas.

f L U f_{LU} f LU ​ = Lane utilization adjustment factor: Accounts for unequal lane loading in multi-lane groups ( 1.00 1.00 1.00 for 1 lane; 0.952 0.952 0.952 for 2 lanes; 0.908 0.908 0.908 for 3 lanes).

f L T f_{LT} f L T ​ = Left-turn adjustment factor: 0.95 0.95 0.95 for protected exclusive left-turn lanes; complex empirical equations for permitted/shared phases.

f R T f_{RT} f RT ​ = Right-turn adjustment factor: 0.85 0.85 0.85 for protected exclusive right-turn lanes; 1.00 − 0.15 P R T 1.00 - 0.15 P_{RT} 1.00 − 0.15 P RT ​ for shared lanes.

f L p b , f R p b f_{Lpb}, f_{Rpb} f L p b ​ , f Rp b ​ = Pedestrian/bicycle conflict adjustment factors for turning movements across crosswalks.

Loading diagram... HCM Signalized Intersection Capacity & Delay Methodology

• Lane Group Capacity, Green Ratios, and Degree of Saturation
• Effective Green Time ( g g g )

Effective green time represents the actual duration of service provided to a movement during each signal cycle: g = G + Y + R c − t L g = G + Y + R_c - t_L g = G + Y + R c ​ − t L ​

Where:

G G G = displayed green interval (s).

Y Y Y = yellow change interval (s).

R c R_c R c ​ = red clearance (all-red) interval (s).

t L t_L t L ​ = total lost time per phase = l 1 + l 2 = l_1 + l_2 = l 1 ​ + l 2 ​ (typically l 1 = 2.0 s l_1 = 2.0\text{ s} l 1 ​ = 2.0 s start-up lost time and l 2 = 2.0 s l_2 = 2.0\text{ s} l 2 ​ = 2.0 s clearance lost time; if Y + R c = t L Y + R_c = t_L Y + R c ​ = t L ​ , then g = G g = G g = G ).

Lane Group Capacity ( c c c )

Capacity ( c c c ) is the maximum hourly volume the lane group can service: c = s × ( g C ) c = s \times \left( \frac{g}{C} \right) c = s × ( C g ​ )

Where C C C is the total cycle length in seconds, and g / C g/C g / C is the green ratio.

Degree of Saturation / Volume-to-Capacity Ratio ( X X X ) X = v c = v s × ( g / C ) = v × C s × g X = \frac{v}{c} = \frac{v}{s \times (g/C)} = \frac{v \times C}{s \times g} X = c v ​ = s × ( g / C ) v ​ = s × g v × C ​

Where v v v is the peak 15-minute demand flow rate in veh/h ( v = V / P H F v = V / PHF v = V / P H F ).

Critical Movement Analysis ( X c X_c X c ​ )

For an entire intersection operating under multi-phase control, the critical degree of saturation ( X c X_c X c ​ ) determines overall system adequacy: X c = ∑ ( v / s ) c i × C C − L = ∑ y c i 1 − ( L / C ) X_c = \frac{\sum (v/s)_{ci} \times C}{C - L} = \frac{\sum y_{ci}}{1 - (L/C)} X c ​ = C − L ∑ ( v / s ) c i ​ × C ​ = 1 − ( L / C ) ∑ y c i ​ ​

Where:

∑ ( v / s ) c i = ∑ y c i \sum (v/s)_{ci} = \sum y_{ci} ∑ ( v / s ) c i ​ = ∑ y c i ​ = sum of flow ratios for critical lane groups across all signal phases.

L = ∑ t L i L = \sum t_{Li} L = ∑ t L i ​ = total lost time per cycle across all critical phases.

If X c > 1.00 X_c > 1.00 X c ​ > 1.00 , the intersection is geometrically and temporally deficient regardless of how green time is allocated.

Control Delay Modeling ( d = d 1 × P F + d 2 + d 3 d = d_1 \times PF + d_2 + d_3 d = d 1 ​ × PF + d 2 ​ + d 3 ​ )

The primary measure of effectiveness for signalized intersections is average control delay ( d d d ) in seconds per vehicle ( s/veh \text{s/veh} s/veh ): d = d 1 × P F + d 2 + d 3 d = d_1 \times PF + d_2 + d_3 d = d 1 ​ × PF + d 2 ​ + d 3 ​

1. Uniform Delay ( d 1 d_1 d 1 ​ )

Uniform delay assumes perfectly uniform, deterministic vehicle arrivals throughout the cycle: d 1 = 0.5 C ( 1 − g C ) 2 1 − [ min ⁡ ( 1 , X ) × g C ] d_1 = \frac{0.5 \, C \left( 1 - \frac{g}{C} \right)^2}{1 - \left[ \min(1, X) \times \frac{g}{C} \right]} d 1 ​ = 1 − [ min ( 1 , X ) × C g ​ ] 0.5 C ( 1 − C g ​ ) 2 ​

2. Progression Adjustment Factor ( P F PF PF )

Progression modifies uniform delay based on arrival platoon quality: P F = ( 1 − P ) f P A 1 − ( g / C ) PF = \frac{(1 - P) f_{PA}}{1 - (g/C)} PF = 1 − ( g / C ) ( 1 − P ) f P A ​ ​

Where P P P is the proportion of vehicles arriving on green, classified into six Arrival Types (AT 1 to AT 6) :

AT 1: Dense platoon arriving during red (worst progression; P F > 1.0 PF > 1.0 PF > 1.0 ).

AT 3: Random, uncoordinated isolated arrivals ( P = g / C ⟹ P F = 1.00 P = g/C \implies PF = 1.00 P = g / C ⟹ PF = 1.00 ).

AT 5: Dense platoon arriving at the onset of green (favorable progression; P F ≈ 0.40 − 0.70 PF \approx 0.40 - 0.70 PF ≈ 0.40 − 0.70 ).

AT 6: Exceptional progression with advanced ITS / dynamic green band ( P ≈ 1.0 P \approx 1.0 P ≈ 1.0 ).

3. Incremental Delay ( d 2 d_2 d 2 ​ )

Accounts for random Poisson arrival fluctuations, individual cycle failures, and sustained oversaturation queues: d 2 = 900 T [ ( X − 1 ) + ( X − 1 ) 2 + 8 k I X c T ] d_2 = 900 T \left[ (X - 1) + \sqrt{(X - 1)^2 + \frac{8 k I X}{c T}} \right] d 2 ​ = 900 T [ ( X − 1 ) + ( X − 1 ) 2 + c T 8 k I X ​ ​ ]

Where:

T T T = analysis period duration in hours ( 0.25 h 0.25\text{ h} 0.25 h for a 15-minute analysis).

k k k = controller actuation parameter ( k = 0.50 k = 0.50 k = 0.50 for fixed-time pretimed signals; 0.04 0.04 0.04 to 0.50 0.50 0.50 for fully-actuated controllers).

I I I = upstream filtering/metering adjustment factor ( I = 1.00 I = 1.00 I = 1.00 for isolated signals; < 1.0 < 1.0 < 1.0 for coordinated arterials with upstream signals).

c c c = lane group capacity (veh/h).

X X X = volume-to-capacity ratio ( v / c v/c v / c ).

4. Initial Queue Delay ( d 3 d_3 d 3 ​ )

Accounts for pre-existing queues ( Q b Q_b Q b ​ ) unmet from the prior analysis period carried over into the current period.

Level of Service (LOS) Criteria for Signalized Intersections

Unlike unsignalized intersections (where LOS F begins at > 50.0 s/veh > 50.0\text{ s/veh} > 50.0 s/veh ), signalized intersections have a higher tolerance threshold due to expected cycle lengths. LOS F begins at > 80.0 s/veh > 80.0\text{ s/veh} > 80.0 s/veh or when v / c > 1.00 v/c > 1.00 v / c > 1.00 .

Level of Service Control Delay ( d d d , s/veh) Operating Conditions & Driver Perception

LOS A ≤ 10.0 \le 10.0 ≤ 10.0 Exceptional progression; almost all vehicles arrive during green. Low cycle length.

LOS B > 10.0 to 20.0 > 10.0 \text{ to } 20.0 > 10.0 to 20.0 Very good progression and/or short cycle lengths. Very few vehicles stop.

LOS C > 20.0 to 35.0 > 20.0 \text{ to } 35.0 > 20.0 to 35.0 Fair progression; noticeable cycle delay. More vehicles stop, but queues clear readily.

LOS D > 35.0 to 55.0 > 35.0 \text{ to } 55.0 > 35.0 to 55.0 Noticeable congestion; high v / c v/c v / c ratios; many vehicles experience signal delay.

LOS E > 55.0 to 80.0 > 55.0 \text{ to } 80.0 > 55.0 to 80.0 Severe delay and long queues; operating at or near capacity ( X ≈ 1.00 X \approx 1.00 X ≈ 1.00 ).

LOS F > 80.0 > 80.0 > 80.0 or X > 1.00 X > 1.00 X > 1.00 Unacceptable delay; severe cycle failures with persistent queue spillback.

• Numerical Step-by-Step Problem: Signalized Capacity & Delay Calculation
• Given Data
• Single isolated through lane group ( N = 1 N = 1 N = 1 )

Cycle length C = 90.0 s C = 90.0\text{ s} C = 90.0 s , Effective green g = 45.0 s g = 45.0\text{ s} g = 45.0 s ( g / C = 0.50 g/C = 0.50 g / C = 0.50 )

Demand volume V = 720 veh/h V = 720\text{ veh/h} V = 720 veh/h , P H F = 0.90 ⟹ v = 800 veh/h PHF = 0.90 \implies v = 800\text{ veh/h} P H F = 0.90 ⟹ v = 800 veh/h

Pretimed controller ( k = 0.50 k = 0.50 k = 0.50 , I = 1.00 I = 1.00 I = 1.00 , T = 0.25 h T = 0.25\text{ h} T = 0.25 h , P F = 1.00 PF = 1.00 PF = 1.00 , d 3 = 0.0 d_3 = 0.0 d 3 ​ = 0.0 )

Adjusted saturation flow rate s = 1 , 800 veh/h/ln s = 1,800\text{ veh/h/ln} s = 1 , 800 veh/h/ln

Step 1: Compute Capacity ( c c c ) c = s × ( g C ) = 1 , 800 × 0.50 = 900 veh/h c = s \times \left( \frac{g}{C} \right) = 1,800 \times 0.50 = 900\text{ veh/h} c = s × ( C g ​ ) = 1 , 800 × 0.50 = 900 veh/h

Step 2: Compute Volume-to-Capacity Ratio ( X X X ) X = v c = 800 900 = 0.8889 X = \frac{v}{c} = \frac{800}{900} = 0.8889 X = c v ​ = 900 800 ​ = 0.8889

Step 3: Compute Uniform Delay ( d 1 d_1 d 1 ​ ) d 1 = 0.5 × 90 × ( 1 − 0.50 ) 2 1 − ( 0.8889 × 0.50 ) = 45 × 0.25 1 − 0.4444 = 11.25 0.5556 = 20.25 s/veh d_1 = \frac{0.5 \times 90 \times (1 - 0.50)^2}{1 - (0.8889 \times 0.50)} = \frac{45 \times 0.25}{1 - 0.4444} = \frac{11.25}{0.5556} = 20.25\text{ s/veh} d 1 ​ = 1 − ( 0.8889 × 0.50 ) 0.5 × 90 × ( 1 − 0.50 ) 2 ​ = 1 − 0.4444 45 × 0.25 ​ = 0.5556 11.25 ​ = 20.25 s/veh

Step 4: Compute Incremental Delay ( d 2 d_2 d 2 ​ ) d 2 = 900 × 0.25 [ ( 0.8889 − 1 ) + ( 0.8889 − 1 ) 2 + 8 × 0.50 × 1.00 × 0.8889 900 × 0.25 ] d_2 = 900 \times 0.25 \left[ (0.8889 - 1) + \sqrt{(0.8889 - 1)^2 + \frac{8 \times 0.50 \times 1.00 \times 0.8889}{900 \times 0.25}} \right] d 2 ​ = 900 × 0.25 [ ( 0.8889 − 1 ) + ( 0.8889 − 1 ) 2 + 900 × 0.25 8 × 0.50 × 1.00 × 0.8889 ​ ​ ] d 2 = 225 [ − 0.1111 + ( − 0.1111 ) 2 + 3.5556 225 ] = 225 [ − 0.1111 + 0.01234 + 0.01580 ] d_2 = 225 \left[ -0.1111 + \sqrt{(-0.1111)^2 + \frac{3.5556}{225}} \right] = 225 \left[ -0.1111 + \sqrt{0.01234 + 0.01580} \right] d 2 ​ = 225 [ − 0.1111 + ( − 0.1111 ) 2 + 225 3.5556 ​ ​ ] = 225 [ − 0.1111 + 0.01234 + 0.01580 ​ ] d 2 = 225 [ − 0.1111 + 0.02814 ] = 225 [ − 0.1111 + 0.1678 ] = 225 × 0.0567 = 12.76 s/veh d_2 = 225 \left[ -0.1111 + \sqrt{0.02814} \right] = 225 \left[ -0.1111 + 0.1678 \right] = 225 \times 0.0567 = 12.76\text{ s/veh} d 2 ​ = 225 [ − 0.1111 + 0.02814 ​ ] = 225 [ − 0.1111 + 0.1678 ] = 225 × 0.0567 = 12.76 s/veh

Step 5: Total Delay and Level of Service d = d 1 ( P F ) + d 2 + d 3 = 20.25 ( 1.00 ) + 12.76 + 0 = 33.01 s/veh d = d_1(PF) + d_2 + d_3 = 20.25(1.00) + 12.76 + 0 = 33.01\text{ s/veh} d = d 1 ​ ( PF ) + d 2 ​ + d 3 ​ = 20.25 ( 1.00 ) + 12.76 + 0 = 33.01 s/veh

Since 20.0 < d ≤ 35.0 s/veh 20.0 < d \le 35.0\text{ s/veh} 20.0 < d ≤ 35.0 s/veh , the lane group operates at LOS C .