
Capacity Constraints and Remedies
Curves
 Grades
 Station stops
 Bridges
 Diamonds
 Track maintenance and renewal

22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
1
PI

100 ft
D
Y
T
T
E

X
M
CT
TC
R





R

Circular Curve
Curve of constant degree (radius)
Used to change alignment direction
May connect to tangents or other curves
Introduced by spirals in higher-speed track
Spiral


Curve whose degree changes uniformly with
distance from origin
Used to:
 transition from tangent alignment to
curve or between consecutive curves
 introduce curve superelevation




Mild curvature:
D ≤ 2º
Medium Curvature: 2º < D ≤ 8º
Sharp Curvature:
8º < D ≤ 12º
Extreme Curvature:
D ≥ 12º


Restricted train speed
Increased train resistance



0.08 lb per train ton per curve degree
Affects acceleration time, power requirements
Increased maintenance
Track alignment and elevation
 Rail and wheel wear


Greater potential for derailment
Direction of curve
R
W
F
(a) Speed < Balanced Speed
R
R
W
F
(b) Speed = Balanced Speed
Relative forces on rails
W
F
(c) Speed > Balanced Speed



Vmax = maximum allowable train speed, mph
Ea = outside rail elevation, inches
Eu = allowable cant deficiency, inches
3 inches for conventional equipment
 4 inches for certified equipment
 higher where approved by FRA


D
= degree of curve
Maximum Track Speed (mph)
140
120
4½” superelevation
100
80
1
2
3
4
5
6
7
Degree of Curvature
Intermodal
Freight
Passenger (conventional eqpt.)
Passenger (tilt eqpt.)
160
60
40
20
0
8
9
10


Increase curve elevation

FRA maximum for track classes 3-5 is 7 inches


Generally requires spiral length adjustment
Consider effect on clearances, structures, crossings
Provide proper spiral design



Qualify equipment for greater cant deficiency
Realign track



Rate of elevation change limits speed
Reduce curve degree
Reduce number of curves
Extend sidings to reduce length of single track

Reduces meet delay in speed limited territory
PVI
G1
G2
PVT

x
PVC

Consists of grade tangents connected by parabolic
vertical curves
Grade tangent has uniform change in elevation
over distance (expressed as percent)
Smooth transition between grade tangents
provided within length of vertical curve
y

L/2
L/2
L


Grade force is 20 lb per train ton per percent
Grades can severely affect:






Maximum sustained train speed (upgrade)
Acceleration (upgrade)
Train speed control (downgrade)
Stopping distance
Train buff and draft forces
Curves add resistance and limit speeds, further
increasing impact of grades
Impact potential of sustained grades:
Low
G ≤ 0.25%
Moderate 0.25% < G ≤ 0.75%
High
0.75% < G ≤ 1.5%
Very High
G> 1.5%




Ruling grade: train with minimum P/W ratio
can crest at crawl speed within motive power
short-time limits
Momentum grade: train with minimum P/W
ratio will crest with some speed reduction from
track speed
Helper grade: train gets temporary additional
power added to help crest grade
Riprap territory: undulating profile requires
care to control buff/draft forces in long trains

Raise P/W ratio on freight trains



Increase power and tonnage on freight trains



May increase speeds on ascending grades
Reduce need for capacity consuming helper and
doubling operations
Longer trains can reduce train volume, free up slots
Especially useful with distributed power
Avoid stopping train on severe upgrades
Provide operating authority to pass restricting
signals at low speed
 Provide power switches at sidings


Change alignment to reduce grade
Typically involves major capital investment
 May increase track length, curvature
 Potential complications, delays from R-O-W
acquisition, permitting
 Tunneling, large cuts can introduce additional
maintenance issues
 Requires careful assessment of economics


Lengthening vertical curves
Improves train handling
 Increases ride comfort at speed



Provide multiple main tracks on long grades to
permit passes and overtakes of slow trains
Provide auxiliary tracks at top and bottom of grade
to:
Clear helper movements
 Reduce delay by trains requiring setup/release of
retainers
 Prevent blockages while doubling


Electrification
Allows increase in train power, regenerative braking
 Major capital investment, economics sensitive to fuel
prices




Each stop requires time for deceleration, station
dwell, and acceleration

Average train speed decreases as number and spacing of
stations increases

Close spacing may not permit train to accelerate to track
speed between stations

Inefficient platform configuration may increase dwell
Stopping trains may delay other traffic
Through trains may have to slow at stations to
reduce risk to passengers


Provide train P/W ratio to achieve performance
goals considering desired dwell time and station
spacing
Provide for meets and passes at stations where
warranted by traffic demands
Sidings
 Multiple main track


Optimize platform configuration to minimize
dwell time
Adequate length to match access points with demand
 High-level fastest loading/unloading

22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
16





Reduced train speed due to bridge design or
condition
Restrictions on traction/braking due to bridge
design or condition
Equipment restrictions due to bridge design or
construction
Restricted train speed approaching movable
bridge
Delays imposed by open movable bridges
22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
17

Bridge condition or structural design
inadequate to withstand
Speed related impact loads
 Speed related lateral loads





Reduce load effects on critical structures
Remediate track condition defects
Permit train crew verification of movable
bridge position
Reduce derailment risk at movable span

Types






Lift bridge
Bascule (draw) bridge
Swing bridge
Open/close cycle time
influences delay
Can be significant capacity
constraint with heavy
water traffic
More to go wrong than
conventional designs


Track capacity reduced
by crossing movements
Approaching train
must be protected
against conflicting
movement


May limit speed, increase
occupancy time
High maintenance
location due to impact
loading

Problems increase with
speed
Flangeway

Reduce maintenance requirements



Provide premium components
Replace with One-Way Low Speed (OWLS) design
Replace with turnouts
Improves reliability, operational flexibility
Realignment of track costly, particularly for right-angle
crossings
 Crossing movements still consume capacity




Provide interlocking with distant signals to reduce
approach delay


Automatic-first come, first served
Dispatcher/operator controlled-can prioritize traffic


Costly, uses more real estate
Permanently solves capacity issues
Grade separate




Railroads must inspect and maintain track
Track must comply with federal Track Safety
Standards (49 CFR Part 213)
Track maintenance workers and machinery
must be protected from train traffic in
accordance with 49 CFR Part 214
The impact of these requirements on track
capacity must be considered
22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
22













Inspect track
Service and adjust special trackwork and track appliances
Replace or repair worn track components
Replace failed track components
Keep track in proper gage, alignment, and surface
Maintain stormwater drainage elements
Correct ballast drainage problems
Address subgrade problems
Control vegetation
Manage thermal loads in CWR track
Distribute materials for projects
Repair storm or derailment damaged track
Reconstruct track to higher standards

Characteristics of track system
Rail and rail fasteners
 Crossties
 Ballast








Track horizontal and vertical alignment
Effectiveness of track drainage
Nature of track subgrade
Traffic volume and mix
Maximum train speed
Maximum wheel loading
Climate




Owner sets train speed limits (pax, freight)
Speeds establish federal track class
Track condition must meet requirements
for class
If track condition does not meet
requirements, owner must take immediate
remedial action



Repair
Reduce track class to make defect compliant
Remove track from service
22 September 2010
Track Class
Max. Freight
Speed (mph)
Max. Passenger
Speed (mph)
1
10
15
2
25
30
3
40
60
4
60
80
5
80
90
6
110
110
7
125
125
8
160
160
9
200
200
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
26

Class specific



Non-class specific



Defect may become compliant by reducing track
class (slow ordering)
Examples: gage, alignment, mismatch
Defect is non-compliant regardless of track class
Examples: drainage, vegetation
Speed defined


Defect type requires specific limiting speed
Example: rail defect, minimum curve elevation

Working under traffic conditions






Practical for many types of work
Trains may pass through work site while work is in
progress
Typically requires speed reduction
Need to clear on-track equipment adds delay
Workers must have protection per Part 214
Taking track out of service
Necessary for some times of work
 May simplify Part 214 compliance
 Capacity unavailable until work complete




Limit duration of slow orders for defect
remediation on main tracks
Address root causes of maintenance problems
Minimize on-track time for forces
Employ hi-rail equipment where practical
 Provide nearby clearance location for on-track equipment
 Prefabricate track panels and pre-position materials
 Use high-production equipment and techniques


Schedule work during off-peak periods
Have close liaison between operations and engineering
 Consider need to provide for night work, lower
productivity

22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
29

Consider life-cycle costs of track components
Premium components can reduce maintenance needs
 Include operating cost impacts of maintenance


Employ “blitz” approach


Plan all possible work in zone, perform during shutdown
Design to reduce impacts of maintenance on
operations
Increase spacing between main tracks and sidings
 Provide crossovers in multiple track territory
 Consider maintenance in design of yards and terminals

22 September 2010
SCORT/TRB Rail Capacity Workshop Jacksonville Florida
30