7.1 Intersection Channelization, Turn Lane Design, & Storage Length

Professional Traffic Operations Engineer PTOE

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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

7.1 Intersection Channelization, Turn Lane Design, & Storage Length

Key Takeaways Explain This Topic AI

Channelization separates conflicting vehicular movements, controls intersection approach angles (optimally 90 degrees, minimum 60 to 75 degrees), regulates vehicle speeds, and provides safe refuge for crossing pedestrians.

Auxiliary turn lane total length is governed by the sum of three distinct components: L = L_t + L_d + L_s, comprising taper length (L_t), deceleration length (L_d), and queue storage length (L_s).

Signalized turn lane storage length is sized using the AASHTO queue storage formula: L_s = (1.5 to 2.0) * (v / N) * (C / 3600) * S_L, where S_L is the average vehicle storage length (25 ft/veh for passenger cars, 40 to 50 ft for heavy trucks).

Dual turn lanes are typically warranted when turning design volumes exceed 300 veh/h; they require minimum 11 to 12 ft lane widths and a minimum 3 ft lateral swept path clearance between turning design vehicles (e.g., WB-62/67 turning concurrently with an SU-30).

Last updated: August 2026

7.1 Intersection Channelization, Turn Lane Design, & Storage Length

PTOE Exam Focus: Intersection geometric design questions rigorously test candidates on channelization principles, turn lane length decomposition ( L = L t + L d + L s L = L_t + L_d + L_s L = L t ​ + L d ​ + L s ​ ), AASHTO deceleration tables, Poisson queue storage derivations ( 1.5 – 2.0 × 1.5\text{--}2.0\times 1.5 – 2.0 × average cycle arrivals), dual left-turn lane warrants, swept path tracking, and raised island dimensions.

1. Principles & Objectives of Intersection Channelization

Channelization is the separation or regulation of conflicting traffic movements into definite paths of travel by using pavement markings, raised islands, or curb features. In accordance with AASHTO Green Book and TRB guidelines, channelization achieves several vital operational and safety objectives:

Separation of Conflict Points: Isolates merging, diverging, and crossing conflicts in space and time, preventing multiple simultaneous conflicts.

Control of Intersection Angle: Aligns crossing streams as close to 90 ∘ 90^\circ 9 0 ∘ as practical ( 75 ∘ to 90 ∘ 75^\circ\text{ to }90^\circ 7 5 ∘ to 9 0 ∘ preferred; absolute minimum 60 ∘ 60^\circ 6 0 ∘ ). Skewed intersections ( < 60 ∘ < 60^\circ < 6 0 ∘ ) severely increase crossing distance, expand the conflict zone, distort driver line of sight (forcing severe neck rotation), and lengthen signal clearance intervals ( Y + R c Y + R_c Y + R c ​ ).

Reduction of Excessive Pavement Area: Prevents erratic vehicle wandering and uncontrolled maneuvers across large open asphalt expanses.

Speed Management & Deflection: Encourages vehicles to enter turning roadways at controlled, predictable speeds by introducing entry curvature.

Pedestrian Refuge: Provides protected physical refuge areas within multi-lane crossings, allowing pedestrians to cross one direction of traffic at a time.

Prohibition of Prohibited Movements: Physically prevents hazardous maneuvers such as wrong-way movements, illegal left turns, or cutting across through lanes.

Location for Traffic Control Devices: Creates optimal physical locations for mounting traffic signal poles, stop signs, pedestrian pushbuttons, and overhead sign structures. Conventional Channelized Right-Turn

• |
• Through Lanes | Through Lanes
• =======================+=======================
• | /| (Island Offset 2-3 ft)
• ----------------------+---/ |
• Right-Turn Bay ------> | / | <-- Raised Triangular
• =======================+-- | Island (>= 50-100 sq ft)
• | / |
• |/____|
• 2. Channelization Island Geometric Standards

AASHTO establishes strict dimensional thresholds for raised channelization islands to ensure they are visible, maintainable, and safely traversable:

Corner Triangular Islands: Must have a minimum surface area of 50 ft 2 50\text{ ft}^2 50 ft 2 on urban curbed intersections, though 75 to 100 ft 2 75\text{ to }100\text{ ft}^2 75 to 100 ft 2 is strongly preferred (especially if accommodating pedestrian cut-through ramps). On rural or high-speed intersections, the minimum island area is 100 ft 2 100\text{ ft}^2 100 ft 2 .

Divisional & Median Islands: Raised median separators should have a minimum width of 4 ft 4\text{ ft} 4 ft (preferably 6 to 8 ft 6\text{ to }8\text{ ft} 6 to 8 ft to accommodate pedestrian refuge and traffic control hardware) and a minimum length of 100 ft 100\text{ ft} 100 ft on high-speed approaches.

Island Curb Offsets: To prevent tire scrubbing and high-speed curb impacts, the nose of a raised island must be offset laterally from the adjacent through travel lane edge line by 2 to 3 ft 2\text{ to }3\text{ ft} 2 to 3 ft (minimum 2 ft 2\text{ ft} 2 ft in urban areas, 3 to 6 ft 3\text{ to }6\text{ ft} 3 to 6 ft in rural/high-speed areas).

3. Auxiliary Turn Lane Length Formulation

The total design length ( L total L_{\text{total}} L total ​ ) of a dedicated left-turn or right-turn auxiliary lane consists of three functional components: L total = L t + L d + L s L_{\text{total}} = L_t + L_d + L_s L total ​ = L t ​ + L d ​ + L s ​

Where:

• L t L_t L t ​ = Taper length (ft)
• L d L_d L d ​ = Deceleration length (ft)

L s L_s L s ​ = Queue storage length (ft) |<-------------------------------- L_total -------------------------------->|

• |<---- L_t ---->|<---------------- L_d ---------------->|<------- L_s ------>|
• Taper Area Braking & Deceleration to Stop Queued Vehicles Storage
• (8:1 to 15:1) (Comfortable Decel d = 10 ft/s^2) (1.5 to 2.0 * v_arr * 25 ft)
• =======\ |===================|
• \-----------------------------------------------+-------------------| Stop
• Auxiliary Turn Lane | Queued Vehicles | Line
• ========================================================+===================|
• A. Taper Length ( L t L_t L t ​ )

The taper provides a smooth lateral transition from the through lane into the auxiliary turn lane:

Straight-Line Bay Taper: Commonly designed using standard taper ratios ( N : 1 N:1 N : 1 ). For design speeds V ≤ 30 mph V \le 30\text{ mph} V ≤ 30 mph , taper ratios range from 8 : 1 to 10 : 1 8:1\text{ to }10:1 8 : 1 to 10 : 1 . For design speeds V ≥ 45 mph V \ge 45\text{ mph} V ≥ 45 mph , taper ratios range from 15 : 1 to 25 : 1 15:1\text{ to }25:1 15 : 1 to 25 : 1 .

Reverse Curve Taper (Symmetrical Curves): Preferred on high-speed facilities to provide comfortable lateral acceleration ( a lat ≤ 3.0 ft/s 2 a_{\text{lat}} \le 3.0\text{ ft/s}^2 a lat ​ ≤ 3.0 ft/s 2 ). Taper length is computed as L t = 8 ⋅ R ⋅ W L_t = \sqrt{8 \cdot R \cdot W} L t ​ = 8 ⋅ R ⋅ W ​ where W W W is lane width and R R R is curve radius.

AASHTO Rule of Thumb: For single turn lanes ( W = 12 ft W = 12\text{ ft} W = 12 ft ), typical urban bay tapers are 50 to 100 ft 50\text{ to }100\text{ ft} 50 to 100 ft , while suburban/rural tapers are 100 to 180 ft 100\text{ to }180\text{ ft} 100 to 180 ft .

B. Deceleration Length ( L d L_d L d ​ )

Deceleration length represents the distance required for a vehicle to decelerate from the roadway design operating speed ( V V V ) to a complete stop ( 0 mph 0\text{ mph} 0 mph ) or to the safe turning design speed ( V turn ≈ 10 – 15 mph V_{\text{turn}} \approx 10\text{--}15\text{ mph} V turn ​ ≈ 10 – 15 mph ), assuming comfortable deceleration rates ( d ≈ 10.0 ft/s 2 d \approx 10.0\text{ ft/s}^2 d ≈ 10.0 ft/s 2 ): L d = 1.467 2 ( V initial 2 − V final 2 ) 2 d = 2.151 ( V i 2 − V f 2 ) 20 = 0.1075 ( V i 2 − V f 2 ) L_d = \frac{1.467^2 \left( V_{\text{initial}}^2 - V_{\text{final}}^2 \right)}{2 d} = \frac{2.151 \left( V_i^2 - V_f^2 \right)}{20} = 0.1075 \left( V_i^2 - V_f^2 \right) L d ​ = 2 d 1.46 7 2 ( V initial 2 ​ − V final 2 ​ ) ​ = 20 2.151 ( V i 2 ​ − V f 2 ​ ) ​ = 0.1075 ( V i 2 ​ − V f 2 ​ )

On grade ( G G G , expressed as a decimal): L d = 1.467 2 ( V i 2 − V f 2 ) 2 g ( a g ± G ) L_d = \frac{1.467^2 \left( V_i^2 - V_f^2 \right)}{2 g \left( \frac{a}{g} \pm G \right)} L d ​ = 2 g ( g a ​ ± G ) 1.46 7 2 ( V i 2 ​ − V f 2 ​ ) ​

Note: AASHTO permits a portion of deceleration to occur in the through lane prior to entering the turn bay on low-speed urban streets (typically braking from V V V down to V − 10 mph V - 10\text{ mph} V − 10 mph in the through lane), but on high-speed rural facilities ( V ≥ 45 mph V \ge 45\text{ mph} V ≥ 45 mph ), the entire deceleration maneuver should occur within the auxiliary lane footprint ( L d + L t L_d + L_t L d ​ + L t ​ ).

C. Queue Storage Length ( L s L_s L s ​ )

The storage length must prevent two catastrophic failure modes: (1) Spillover: Turning vehicles overflowing the bay and blocking the through travel lanes; and (2) Starvation/Blockage: Through vehicle queues extending upstream and blocking the entrance to the turn bay.

1. Signalized Intersections (AASHTO / ITE Method):

Storage length is sized based on the 95th-percentile arrival queue during peak periods ( 1.5 to 2.0 1.5\text{ to }2.0 1.5 to 2.0 times the average number of vehicles arriving per cycle): L s = F safety × ( v N × 3600 / C ) × S L = F safety × ( v × C 3600 × N ) × S L L_s = F_{\text{safety}} \times \left( \frac{v}{N \times 3600 / C} \right) \times S_L = F_{\text{safety}} \times \left( \frac{v \times C}{3600 \times N} \right) \times S_L L s ​ = F safety ​ × ( N × 3600/ C v ​ ) × S L ​ = F safety ​ × ( 3600 × N v × C ​ ) × S L ​

Where:

F safety F_{\text{safety}} F safety ​ = Safety factor ( 1.5 1.5 1.5 for moderate risk; 2.0 2.0 2.0 for high reliability / 95th-percentile Poisson arrivals)

• v v v = Design hourly turning volume (veh/h)
• C C C = Traffic signal cycle length (seconds)
• N N N = Number of turning lanes (e.g., N = 1 N = 1 N = 1 for single, N = 2 N = 2 N = 2 for dual turn lanes)

S L S_L S L ​ = Average storage length per vehicle queue spot (standard: 25 ft/veh 25\text{ ft/veh} 25 ft/veh for passenger cars; 40 – 50 ft/veh 40\text{--}50\text{ ft/veh} 40 – 50 ft/veh for heavy commercial vehicles)

2. Unsignalized Intersections (AASHTO 2-Minute Arrival Rule):

For two-way stop-controlled (TWSC) intersections, storage should accommodate arrivals over a 2-minute peak period : L s = 2.0 × ( v 30 ) × 25 ft L_s = 2.0 \times \left( \frac{v}{30} \right) \times 25\text{ ft} L s ​ = 2.0 × ( 30 v ​ ) × 25 ft

Minimum AASHTO storage length on any auxiliary lane is 50 ft 50\text{ ft} 50 ft (2 passenger cars), with 100 ft 100\text{ ft} 100 ft strongly recommended for commercial corridors.

4. Dual & Triple Turn Lane Geometric Controls

When turning volumes exceed the single-lane capacity threshold (typically v ≥ 300 veh/h v \ge 300\text{ veh/h} v ≥ 300 veh/h for left turns, or where signal green time is constrained), dual left-turn lanes (DLT) or dual right-turn lanes are implemented. DUAL LEFT-TURN SWEPT PATHS

• +----------------------------------------+
• Approach Lanes | Inside Lane: SU-30 Design Vehicle |
• ===================+==== | (R_in = 30-50 ft, Track Width 11-12 ft)|
• Inside Left (11') | | +----------------------------------------+
• ------------------+--+ | 3 ft Minimum Lateral Clearance Buffer|
• Outside Left (12') | | +----------------------------------------+
• ===================+==+ | Outside Lane: WB-62 / WB-67 Truck |
• | (R_out = 60-80 ft, Swept Path 14-16 ft)|
• +----------------------------------------+

Critical Geometric Requirements for Dual Turn Lanes:

Swept Path Analysis: The inner lane is typically designed for a Single Unit truck (SU-30) or passenger car, while the outer lane is designed for the design commercial vehicle (WB-50, WB-62, or WB-67). A minimum lateral separation of 3.0 ft 3.0\text{ ft} 3.0 ft (preferably 4.0 ft 4.0\text{ ft} 4.0 ft ) must be maintained between the swept paths of concurrently turning vehicles throughout the turning arc.

Lane Widths: Turn lanes must be at least 11 ft 11\text{ ft} 11 ft , and preferably 12 ft 12\text{ ft} 12 ft (widened along the curve to 13 – 14 ft 13\text{--}14\text{ ft} 13 – 14 ft if curve radii R < 50 ft R < 50\text{ ft} R < 50 ft to accommodate rear wheel off-tracking).

Receiving Throat Width: The receiving roadway must provide at least two full departing lanes plus additional pavement width (minimum 2 – 3 ft 2\text{--}3\text{ ft} 2 – 3 ft gutter pan or curb offset) to receive the off-tracking swept path.

MUTCD Pavement Delineation: Dotted line extensions (MUTCD Section 3B.11, 2 ft 2\text{ ft} 2 ft line, 4 – 6 ft 4\text{--}6\text{ ft} 4 – 6 ft gap) must guide motorists through the intersection to prevent lane encroachment and sideswipe collisions.

AASHTO Minimum Deceleration Lengths (L_d) for Auxiliary Turn Lanes

Design Speed (mph) L_d to Full Stop (0 mph) (ft) L_d to 15 mph Turning Speed (ft) Minimum Urban Taper Ratio Minimum Rural Taper Ratio

• 30 160 110 8:1 15:1
• 35 215 160 9:1 18:1
• 40 275 215 10:1 20:1
• 45 345 285 12:1 22:1
• 50 425 360 15:1 25:1
• 55 510 445 15:1 25:1
• 60 605 540 18:1 30:1

Loading diagram... Components of Auxiliary Turn Lane Geometric Design

5. Worked Calculation Example: Left-Turn Bay Sizing

Problem Statement:

An urban arterial with a design speed of 45 mph 45\text{ mph} 45 mph has a signalized intersection operating on a 100 -second 100\text{-second} 100 -second cycle length ( C = 100 s C = 100\text{ s} C = 100 s ). The design hourly left-turn volume is v = 280 veh/h v = 280\text{ veh/h} v = 280 veh/h with 5 % 5\% 5% heavy commercial trucks. An auxiliary single left-turn bay ( W = 12 ft W = 12\text{ ft} W = 12 ft ) is being designed with full deceleration occurring within the lane (decelerating to a stop, L d = 345 ft L_d = 345\text{ ft} L d ​ = 345 ft ) and a standard 10 : 1 10:1 10 : 1 straight-line bay taper.

Calculate the required taper length ( L t L_t L t ​ ).

Compute the 95th-percentile queue storage length ( L s L_s L s ​ ) using a safety factor of 2.0 2.0 2.0 , assuming passenger car length of 25 ft 25\text{ ft} 25 ft and heavy truck length equivalent of 50 ft 50\text{ ft} 50 ft .

Determine the total required left-turn lane length ( L total L_{\text{total}} L total ​ ).

Step-by-Step Solution:

Taper Length ( L t L_t L t ​ ): L t = W × Taper Ratio = 12 ft × 10 = 120 ft L_t = W \times \text{Taper Ratio} = 12\text{ ft} \times 10 = 120\text{ ft} L t ​ = W × Taper Ratio = 12 ft × 10 = 120 ft

Effective Average Vehicle Length ( S L S_L S L ​ ): S L = ( 1 − 0.05 ) × 25 ft + ( 0.05 ) × 50 ft = 0.95 ( 25 ) + 0.05 ( 50 ) = 23.75 + 2.50 = 26.25 ft/veh S_L = (1 - 0.05) \times 25\text{ ft} + (0.05) \times 50\text{ ft} = 0.95(25) + 0.05(50) = 23.75 + 2.50 = 26.25\text{ ft/veh} S L ​ = ( 1 − 0.05 ) × 25 ft + ( 0.05 ) × 50 ft = 0.95 ( 25 ) + 0.05 ( 50 ) = 23.75 + 2.50 = 26.25 ft/veh

Queue Storage Length ( L s L_s L s ​ ): Average arrivals per cycle ( λ cycle \lambda_{\text{cycle}} λ cycle ​ ): λ cycle = v × C 3600 = 280 veh/h × 100 s 3600 s/h = 7.78 vehicles/cycle \lambda_{\text{cycle}} = \frac{v \times C}{3600} = \frac{280\text{ veh/h} \times 100\text{ s}}{3600\text{ s/h}} = 7.78\text{ vehicles/cycle} λ cycle ​ = 3600 v × C ​ = 3600 s/h 280 veh/h × 100 s ​ = 7.78 vehicles/cycle

Using F safety = 2.0 F_{\text{safety}} = 2.0 F safety ​ = 2.0 for 95th-percentile Poisson queue: N storage = 2.0 × 7.78 = 15.56 ≈ 16 vehicles N_{\text{storage}} = 2.0 \times 7.78 = 15.56 \approx 16\text{ vehicles} N storage ​ = 2.0 × 7.78 = 15.56 ≈ 16 vehicles L s = 16 vehicles × 26.25 ft/veh = 420 ft L_s = 16\text{ vehicles} \times 26.25\text{ ft/veh} = 420\text{ ft} L s ​ = 16 vehicles × 26.25 ft/veh = 420 ft

Total Turn Lane Length ( L total L_{\text{total}} L total ​ ): L total = L t + L d + L s = 120 ft + 345 ft + 420 ft = 885 ft L_{\text{total}} = L_t + L_d + L_s = 120\text{ ft} + 345\text{ ft} + 420\text{ ft} = 885\text{ ft} L total ​ = L t ​ + L d ​ + L s ​ = 120 ft + 345 ft + 420 ft = 885 ft

Components of Total Left-Turn Lane Length at 45 mph (Example)