t5 alignment lackey

Light Rail Transit Facilities Design Course

Light Rail Alignment Design May 22, 2010

John A. Lackey, PE

Senior Vice President

David Evans and Associates, Inc.

2


Light Rail Transit Alignment Design 3

Light Rail Transit Alignment Design Discussion Topics

• Design vehicle clearance and loading

• Types of alignments and typical cross sections

– Open track

– In-street alignments

– Adjacent to freight railroads

– Elevated

– Underground

• Alignment Geometry



Light Rail Transit Alignment Design Design Vehicle Clearance and Loading

Vehicle characteristics and dimensions

– Vehicle loads

– Wheel/track relationship

– Vehicle performance

– Dynamic envelope

– Guideway clearances



General Vehicle Characteristics

• Bi-directional • Articulated • Operated as coupled-trains • Three trucks, two axles per truck • Pantograph • High or low floor, or combination



Accessibility



Comparison of Light Rail Vehicles

Sample subhead




– Vehicle characteristics and dimensions

– Vehicle loads







Vehicle Loads

•AW0 - Empty vehicle operating weight •AW1 - (Seated load)

– Fully seated passengers + AWO

•AW2 - (Design load) – Standing passengers at 4/m2 + AW1

•AW3 - (Crush load) – Standing passengers at 6/m2 + AW1

•AW4 - (Structure design load) – Standing passengers at 8/m2 + AW1





– Vehicle loads







Wheel/Track Relationship

• Vehicle wheel profile

• Rail profile

• -

• Curved track





– Vehicle loads







Vehicle Performance

• Suspension

– Primary

– Secondary

• Other loads affecting performance

– Trucks

– Load leveling

• Performance on alignment

– Accel/decel

– Operating speed

– Track curvature and gradient

– Train size





– Vehicle loads







Dynamic Envelope

• VDE • Other factors:

– Overhang on curves – Lean due to suspension, track superelevation – Track and wheel wear – Wheel/track spacing – Passenger loading

• Maintenance values: – Lateral wheel wear - – Wheel-to-rail side play - – Radial wheel wear -





– Vehicle loads







Guideway Clearances

CE = VDE + OWF + RC

– CE - Clearance Envelope

– VDE - Vehicle Dynamic Envelope

– OWF - Other Wayside Factors

– RC - Running Clearance



CE = VDE + OWF + RC

OWF = CT + MT + CW

– CT - Construction Tolerance

– MT - Maintenance Tolerance

– CW - Chorded Construction of Walls

• (effects of track curvature and superelevation)



Guideway Clearances

• CT = allowable deviations from design positions – Track -

– Poles, signal equipment -

– Walls -

• MT = allowable deviations from constructed condition: – Ballasted track -

– Embedded track or Direct Fixation -

– Lateral rail wear -

– Vertical tolerance -

– Cross level variance, ballasted -

– Cross level variance, DF -

• CW = effects of track curvature and superelevation



CE = VDE + OWF + RC

RC = Running Clearances:

– RC to signals, signs, poles, etc. -

– RC to emergency walkway envelope -

– RC to bridge parapet, walls, other structures -

– -



Track at Station Platform



Light Rail Transit Alignment Design Types of Alignments and Typical Cross Sections

– Open Track

– In-Street Alignments

– Adjacent to Freight Railroads

– Elevated

– Underground



Typical Ballasted Section



Open Track Ballasted



Typical LRT Median



Open Track Ballasted



Open Track Direct Fixation (DF)



Open Track Direct Fixation




– Open Track



– Elevated

– Underground



Embedded Track (Paved)

In-Street Alignments




– Open Track



– Elevated

– Underground



Adjacent to Freight Railroads



Adjacent to Freight Railroads Grade Separation




– Open Track



– Elevated

– Underground



Elevated (Bridges)



Elevated (Guideway and Station)




– Open Track



– Elevated

– Underground



Underground (Tunnel)



Below Ground - Depressed



Light Rail Transit Alignment Design

Alignment Geometry

– Design Criteria and Standards

– Horizontal Alignment

– Vertical Alignment

– In-Street Running Impacts and Considerations

– Station Requirements




Alignment Geometry








Horizontal Alignment

• Clearances

• Speed

• Tangents

• Circular Curves

• Superelevation

• Spiral Transitions

• Special Track




Superelevation




Special Track




Special Track

– Precurved Rail

•

– Restraining Rail

•

– Emergency Guard Rail

– Turnouts and Crossovers




Alignment Geometry








Vertical Alignment

Profile Grades

Desirable Absolute Condition Maximum Maximum Maximum Mainline Track 3.5% 5.0% 7.0% Stations 0/5% 3.0% 4.5% Yard 0.0% 0.5% 1.0% Storage Track 0.0% 0.25% 0.5%

Minimum grade for drainage = 0.2%



Vertical Alignment

Vertical Curves

Minimum Length as function of speed: – L = 70 (G1 - G2) for V > 35 – L = 40 (G1 - G2) for 15 < V < 35 – L = 20 (G1 - G2) for V < 15

Minimum length of any vertical curve:

– Desirable – Minimum – Absolute



Vertical Alignment

Other Considerations

– Station platforms:

• Tangent grade 0 % to 2.0 %

•

– Combined vertical and horizontal curves

•

•

•




Alignment Geometry








In-Street Impacts and Considerations

• Operational policies

• Physical and design constraints

• Right-of-Way




Alignment Geometry








Questions

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