COPYRIGHT AREMA 2012 9: 1 of 29 Module 9: Railway Track
Alignment Design Slide 2 COPYRIGHT AREMA 2012 9: 2 of 29 Objectives
Railway vs. Highway Horizontal Curves Vertical Curves
Superelevation Maximum Grade Practical Tips Cardinal Rules Slide 3
COPYRIGHT AREMA 2012 9: 3 of 29 Railway Alignment Safe to operate
under all weather conditions Minimum costs for: Construction
Maintenance Operation Several critical design considerations Speed,
type and volume of traffic Space considerations (Right-of-Way)
Environmental concerns Politics and land use issues Other economic
criteria Slide 4 COPYRIGHT AREMA 2012 9: 4 of 29 Railway vs.
Highway Railway alignment differs from Highway: Operator has no
horizontal control Higher mass/power ratio flatter grade required
Rail 286,000 lbs vs. 80,000 lbs gross truck Rail up to 70 ft. truck
centers higher curve resistance Extremely long stopping distance
Faster trains require tighter tolerances in track alignment
Opposing trains may operate on same track Slide 5 COPYRIGHT AREMA
2012 9: 5 of 29 Mainlines Critical issues Maximum curvature
determines speed Speed (required) determines curvature Terrain
governs size of curves Train tonnage and maximum lengths Traffic
volumes and train makeup for capacity (number of tracks, density of
crossovers, etc.) Slide 6 COPYRIGHT AREMA 2012 9: 6 of 29
Horizontal Curve Slide 7 COPYRIGHT AREMA 2012 9: 7 of 29 Horizontal
Curves Horizontal curve definition: Railways: Based on D and
defined as angle subtended by 100-ft. chord. R (ft.) = 50 ft. / sin
( D / 2 ) - Highways: Based on angle subtended by 100-ft. arc. D
(hwy) = 5729.578 / R Practical Tip No. 1 Railroads use Degree not
Radius Slide 8 COPYRIGHT AREMA 2012 9: 8 of 29 Reverse Curve Slide
9 COPYRIGHT AREMA 2012 9: 9 of 29 Reverse Curves Photo by Bob
IcePhoto by Dave Clark Slide 10 COPYRIGHT AREMA 2012 9: 10 of 29
Avoid Reverse Curves Objectionable in track-train dynamics Reversed
track twist of spiral requires high maintenance Railways need
tangent track between curves of opposite directions: Recommended
100 ft (Practical Tip No. 2) Recommended 2 second transit time for
passenger operations Not less than the length of longest railcar
expected to traverse the curves Slide 11 COPYRIGHT AREMA 2012 9: 11
of 29 Railway Spirals Location for spirals in railroads: In main
track between tangents and curves Between curves of different
curvatures in compound curves Form of railway spiral should have a
linear rate of curvature increase Clothoid Spiral is almost
exclusively used in Canada and the U.S.A. Slide 12 COPYRIGHT AREMA
2012 9: 12 of 29 Spiral Transition Curves Spirals provide Gradual
change from tangent to curve A desirable length for super-elevation
run-off Highway spiral length: Ls = A 2 / RA = spiral parameter
Railways use the higher of two formula: To limit unbalanced lateral
acceleration acting on passengers to 0.03 g per second: Ls = 1.63 E
u V E u = unbalanced elevation (in.) To limit track twist to 1 inch
in 62 feet: Ls = 62 E a E a = actual elevation (in.) Slide 13
COPYRIGHT AREMA 2012 9: 13 of 29 Superelevation / Cross Level
Highways Equilibrium elevation e: e = B V 2 / (32.16 R ) V in
ft./sec; e, B, R in ft. Highways use cross level e = e / B and side
friction factor f to overcome centrifugal force: e + f = V 2 /
(14.65 R ) V in mph; R in ft. Slide 14 COPYRIGHT AREMA 2012 9: 14
of 29 Super-elevation / Cross Level Railways Elevation of Curves
(MRE 5.3.3) e= Bv 2 /32.2R e = Equilibrium elevation in feet B =
Bearing Distance in feet center to center of rails 4 11- for
standard gauge track v = Velocity in feet per second R = Radius in
feet This converts to E = 0.0007 V 2 D V in mph; D = Degree E =
Equilibrium elevation in inches Slide 15 COPYRIGHT AREMA 2012 9: 15
of 29 Unbalanced Elevation Different maximum allowed speeds for
different trains on the same track: Passenger Express freight
General freight Balance flange wear of both rails Slide 16
COPYRIGHT AREMA 2012 9: 16 of 29 Maximum Curvature Good designers
limit curvature to: High Speed Passenger1 Curve Main Lines -
prairie2 Curve Main Lines - mountain4 Curve (if possible) Branch
Lines 25 mph8 Curve Yard Tracks12 Curve (varies) Over 13 curves may
cause operational difficulties. Slide 17 COPYRIGHT AREMA 2012 9: 17
of 29 Maximum Superelevation Highway Authorities: Range 0.06 to
0.08 ft./ft. as maximum FRA: 8 cross-level for Class 1 & 2 30
mph psgr., 25 mph frt. 7 for Class 3 through 5 tracks Transport
Canada: 6 for tracks of all Classes Railways usually adopt 1 less
than regulatory limit to ensure compliance if the tracks move due
to use or over winter Railways often superelevate curves even when
not required to prevent reverse elevation due to settlement Slide
18 COPYRIGHT AREMA 2012 9: 18 of 29 Vertical Curves Highway
vertical curves: L = K A K = coefficient defining length per
gradient change A = algebraic difference of grade (%) Railway
vertical curves old formula: L = D / R D = algebraic difference of
grade (ft. per 100-ft. station) R = rate of change per 100-ft.
station 0.05 ft. per station for crest on main track 0.10 ft. per
station for sag on main track Secondary line may be twice those for
main line Railways moving to shorter vertical curves Slide 19
COPYRIGHT AREMA 2012 9: 19 of 29 New Shorter Vertical Curves Old
railway formula developed in 1880s for link and pin couplers in
those days Present day couplers can accommodate shorter vertical
curves New formula developed in recent years : L = 2.15 V 2 D / A V
= train speed in mph D = algebraic difference of grade in decimal A
= vertical acceleration in ft./sec 2 0.1 ft./ sec 2 for freight,
0.6 ft./ sec 2 for psgr or transit Practical Tip No. 3 Verify RR
uses new equation Slide 20 COPYRIGHT AREMA 2012 9: 20 of 29 Design
Grade for Railways Maximum design grade: Primary Line = 0.4%
railway 3.0% highway Secondary Line = 1.0% railway 6.0% hwy Ideal
maximum for railway grade: Trains can roll safely down 0.3% grade
without wasting energy on brakes Tracks dedicated for passenger or
transit use only may have steeper grade Slide 21 COPYRIGHT AREMA
2012 9: 21 of 29 Stationing Milepost and Stationing might not
increase in the same direction Milepost not accurate Establish
stationing from a set object Equations Practical Tip No. 4 Know
when to station to the 100th Slide 22 COPYRIGHT AREMA 2012 9: 22 of
29 Clearance Specific clearances necessary for safe operations Size
of car clearance envelope is based on dimensions of: Locomotives
Cars Potential large loads Requirements set by several agencies
Slide 23 COPYRIGHT AREMA 2012 9: 23 of 29 Horizontal Clearance
Constant on tangent track Additional clearance: In curves for car
end swing and car overhang In superelevated tracks to provide room
for cant Slide 24 COPYRIGHT AREMA 2012 9: 24 of 29 Vertical
Clearance Constant on tangent track Additional clearance: In sag
vertical curves In superelevated tracks For specialized equipment
To provide threshold for future track maintenance and equipment
changes Slide 25 COPYRIGHT AREMA 2012 9: 25 of 29 Turnouts Whats
wrong with this picture? Slide 26 COPYRIGHT AREMA 2012 9: 26 of 29
21 Cardinal Rules SEE YOUR HANDOUTDISPLAY IT SOMEWHERE CLOSE AND
SHARE IT WITH YOUR FRIENDS! Slide 27 COPYRIGHT AREMA 2012 9: 27 of
29 Some Design Software There are two major computer aided drafting
(CAD) programs used in the industry AutoCAD (railroads, private
industries) Microstation (state D.O.T.s, government) Each program
has add-on Design software programs that are used for designing the
horizontal alignments, vertical profiles, cross- sections Bentley
http://www.bentley.com/en-UShttp://www.bentley.com/en-US Rail
Track: (specifically rail design) Civil 3D Geopak: (highway or rail
design) Inroads: (highway or rail design) Autodesk
http://usa.autodesk.com/http://usa.autodesk.com/ Civil 3D (highway
or rail design) Slide 28 COPYRIGHT AREMA 2012 9: 28 of 29 Design
Software Views 3-D modelRail Track Interface Slide 29 COPYRIGHT
AREMA 2012 9: 29 of 29 QUESTIONS? Author: Charley Chambers, P.E.
Hanson Professional Services, inc. (425) 576-1690
[email protected] Revisions: John G. Green, Ph.D., P.E.
CH2M Hill, inc. (312) 348-5030 [email protected] Slide 30
COPYRIGHT AREMA 2012 9: 30 of 29 REVISION HISTORY
