215 Jamestown Park, Ste. 100 ◦ Brentwood, TN 37027 ◦ Phone (615) 373-8532

7340 E. Caley Ave., Ste. 200 ◦ Centennial, CO 80111 ◦ Phone (303) 771-9150

7080 Landmark Place ◦ Helena, MT 59601 ◦ Phone (406)449-6216

Creosote-Treated Ties

End-of-Life Evaluation

Stephen Smith1and Chris Bolin2

Introduction

The full life cycle of creosote-treated railroad ties includes: the growth of trees on forested land;

harvest of logs; milling to create ties and lumber; treatment of ties with creosote; use of the ties

by the railroads as part of the railroad bed; and, at the end of their use lives, disposal or use as an

energy source. End-of-life alternatives include: recycling ties to produce useful energy,

disposing ties in landfills, and legacy ties along the railroad’s right-of-way. This paper reports

the results of evaluation done to determine some of the energy and environmental consequences

of these end-of-life options. Calculations for this paper were completed in spreadsheet tables

that are available from the authors.

Description of Creosote-Treated Ties

Crossties are primarily made of hardwood species, mostly species of oak. Approximately 8

percent are made of softwood species, predominantly Douglas fir. After milling, ties are dried

either by air seasoning in stacks open to the air for several months or by the Boulton process, in

which ties are heated in the treating cylinders immersed in liquid creosote and under vacuum to

drive off excess moisture. The “dry” ties average approximately 40 to 50 percent moisture on a

dry wood basis.

Ties are treated by pressure impregnation of creosote preservative. Standards for treatment are

stated in the American Wood Protection Association (AWPA) standards. Most ties are treated to

a gauge retention of seven (7) pounds per cubic foot (pcf) of wood with refractory species, such

as white oak and Douglas-fir, being treated to refusal. Gauge retention is calculated simply as

1

Stephen Smith, P.E. AquAeTer, Helena, MT. E-mail: stephentsmith@earthlink.net.

2 Chris Bolin, AquAeTer, Centenial, CO. E-mail: cbolin@aquaeter.com.
Creosote-Treated Railroad Ties Page 2 of 10

End-of-Life Evaluation February 18, 2010

the amount of creosote injected into a charge of wood divided by the volume of wood in the

charge. Since some wood species are “refractory”, meaning the wood is resistant to treatment,

the actual U.S. average creosote retention in ties is probably in the range of 5 to 6 pcf. 5.5 pcf is

assumed in this evaluation.

Ties vary in size depending on use. The standard or “typical” tie measures 7-inches high by 9-

inches wide by 8.5-feet long. The volume for this size tie is 3.72 cubic feet. Thus, the average

new tie contains approximately 20 pounds of creosote (5.5 lb/ft3x 3.72 ft3).

The composition of a treated tie changes from initial treatment through the use life such that it is

different at the end-of-life. Ties spend their use life in an extreme environment; placed

horizontally, the top surface fully exposed to sun and weather, the sides and bottom embedded in

ballast rock, repeatedly heated, cooled, wetted, and dried, in varying climates, while being

subjected to repeated compression and bending stresses as they support the transport of millions

of tons of freight each year. A portion of the creosote is lost due to volatilization, and biological

and photo-chemical degradation that takes place on the surface of the ties and to a lesser extent

in surrounding ballast.

Kohler and Kunniger (2003) determined creosote levels in ties following 2, 5, 10, and 32 years in

service. Although the loss rate early in life was higher, the long term straight line average at 32

years was approximately 32 percent loss. Thus, a simple approximation of 1 percent loss of

creosote per year of service and an average service life of 35 years supports an estimate that 35

percent of the creosote initially injected into the ties is lost during the use life. All of the

creosote loss is assumed to degrade or oxidize so that the carbon fraction is eventually converted

to carbon dioxide.

Some biological decay of the wood also occurs during the use life. While this fact is clear by

observation of some used ties, we are not aware of any data to document the amount of wood

mass typically lost. For this evaluation, we assume 5% is decayed with that fraction of the wood

carbon converted through aerobic processes to carbon dioxide.

The moisture content of the ties will change over time to be in equilibrium with the environment.

While this will vary significantly for used ties, an average of 20 percent moisture for ties at endof-life is assumed in this evaluation.

The average composition of ties at life stages of untreated, newly treated, and end-of-use are

shown in Table 1.
Creosote-Treated Railroad Ties Page 3 of 10

End-of-Life Evaluation February 18, 2010

Table 1 - Composition of Ties by Life Stage

Tie Components Untreated, green Treated Loss/ change

in Use

Used ties

(lb/tie) (lb/tie) (lb/tie)

Wood (dry mass) 148 148 5% 141

Water (% of dry mass) 70% 40% 20%

Water mass 104 59 28

Creosote mass 0 20 35% 13

Whole tie 252 228 182

Impact Indicators

As noted above, each end-of-life option has consequences. The following indicators of potential

impacts (consequences) are evaluated for each option.

 Fossil Energy Use – Fossil energy is a non-renewable resource. Use of fossil energy is a

measure of resource depletion. When renewable resources, such as wood, are

beneficially used, they offset fossil fuel use and reduce resource depletion.

 Greenhouse Gases – Global warming is thought to be at least partially caused by human

(anthropogenic) releases of gases that trap heat within the earth’s atmosphere, called

greenhouse gases (GHG). Carbon dioxide is the reference compound used to assess

warming impact. Methane is released in much smaller quantities, but is estimated to have

21 times the warming potential of carbon dioxide on a mass basis. Wood is biogenic,

rather than fossil fuel. Wood combustion results in the release of carbon dioxide to the

atmosphere in a manner similar to other fuels; however, because the carbon in wood was

first removed from the atmosphere through photosynthesis as the trees grew and would

naturally return to the atmosphere when the trees die and either rot or burn, the use of

wood fuel is considered carbon neutral. Use of wood fuel therefore does not increase

GHG emissions.

 Acidification – Acid rain or precipitation impacts include building corrosion, water body

acidification, vegetation effects, and soil effects. Acid forms in the atmosphere due to

releases of compounds such as nitrogen oxides, hydrochloric acid, and sulfur oxides.

Combustion of fuel results in emissions that contribute to acidification. The relative

potency of each compound to cause acidification, in units of hydrogen ion mole

equivalents per pound released (H+mole-eq) has been summarized in the USEPA Tool for

the Reduction and Assessment of Chemical and Other Environmental Impacts (TRACI)

model. These factors have been applied to standard emission rates for natural gas, wood,
Creosote-Treated Railroad Ties Page 4 of 10

End-of-Life Evaluation February 18, 2010

and coal combustion boilers to evaluate the potential acidification impact of each disposal

option.

Tie Impact Indicators Prior to End-of-Life

The wood in each tie contains 71 pounds of carbon that equates to the removal of 260 pounds of

carbon dioxide during tree growth. Each tie also contains 13 pounds of fossil carbon in the

creosote. Thus, treated ties begin with negative 260 pounds of CO2 and this value increases

through life as the fossil components decay or are combusted. While in use, 5 percent of the

wood and 35 percent of the creosote are converted to carbon dioxide, raising the GHG emissions

by 34 pounds for a net of negative 226 pounds.

Recycle Ties for Energy Recovery

Used ties have value as a source of energy. The heat value of wood varies generally from about

4,500 to 8,000 BTU per pound (9,000 BTU per pound at zero percent moisture), depending on

moisture content. Creosote adds to the heat value with approximately 12,500 BTU per pound.

Thus, each tie offers approximately 1.4 million BTU (MMBTU) of heat energy.

Ties may be used as fuel in a facility designed specifically to burn ties, in industrial wood fired

boilers, in utility boilers co-fired with coal, or other solid fuel combustion systems, such as

cement kilns. With new technology, ties are being used in gasification facilities to produce

electric energy or liquid biofuel. In a cogeneration (also called combined heat and power)

facility, ties and other fuel, as applicable, are burned to produce high pressure steam that drives a

turbine to produce electricity while some or all of the low pressure steam from the turbine is used

for process heating, thereby increasing the overall thermal efficiency of energy conversion.

When ties are burned beneficially as fuel, they offset fossil fuel that would otherwise have been

used to produce the same energy. The energy value of one tie is approximately equal to that of

125 pounds of coal.

Since the wood fuel is carbon neutral, for each tie burned for energy recovery, only the creosote

portion is considered a fossil fuel that results in the addition of approximately 39 pounds of

carbon dioxide to the atmosphere. The carbon dioxide from burning coal of equal energy would

be approximately 288 pounds. Thus, each tie used for energy results in a net offset of carbon

dioxide emissions of approximately 249 pounds.
Creosote-Treated Railroad Ties Page 5 of 10

End-of-Life Evaluation February 18, 2010

Acidifying emissions from burning wood (13 H+-mole-equivalents/tie) are less than for burning

an equivalent amount of coal (136 H+-mole-eq/tie); thus, use of ties for fuel results in lower net

acidifying emissions.

Landfill Disposal of Ties

Following removal from the railroad bed, used ties are collected into either trucks or railcars and

are transported to landfill disposal sites. At the landfills, ties are placed and buried with other

construction and demolition (C&D) waste and/or municipal solid waste for long term disposal.

Within the landfill, some of the wood and creosote will degrade anerobically, producing both

carbon dioxide and methane. Some of the methane will further degrade to CO2, some will be

collected and burned, and some will be emitted to the atmosphere. The carbon dioxide from

wood degradation is considered carbon neutral and does not count as a GHG. However, the

methane would not result from natural decay in the forest, which is mainly aerobic, so is

considered a GHG.

This evaluation considers ties being disposed in an assumed “typical” mix of 55 percent

municipal waste landfills and 45 percent C&D landfills. Laboratory data of the fate of wood in

landfills (EPA, 2006) is used to model the fate of ties in landfills. 77 percent of the mass is

assumed to remain in long term storage (sequestered) in the landfill. Of the rest, half is decayed

into carbon dioxide and half to methane. Of the methane, 75 percent is collected from municipal

waste landfills while none is collected from the C&D landfills. We further assume that of the

methane not collected, 10 percent from municipal waste and 25 percent from C&D landfills

decays to carbon dioxide and the rest is emitted to the atmosphere as a GHG. Of the collected

methane, 60 percent is assumed to be used beneficially as a fuel and the rest burned by flares

with no beneficial use, meaning that all of this is converted to CO2.

From the model, each tie disposed in a landfill will have 5.5 pounds of methane released to the

atmosphere, 4.9 pounds of methane captured, of which 1.9 pounds are burned in a flare, and 3.0

pounds are used beneficially offsetting the use of an equal amount of natural gas. Approximately

44 pounds of biogenic carbon dioxide and 7.0 pounds of fossil carbon dioxide will be emitted.

However, the GHG emission of methane and fossil carbon dioxide will be 116 pounds of CO2-

equivalent less 8 pounds of CO2 for offset natural gas combustion for a net of 108 pounds CO2-

equivalent of GHG.

Legacy Ties in the Right-of-Way

It is unknown to what extent legacy ties exist along the right-of-way. Assuming that following

removal from the rail bed a small number of used ties remain along the railroad within the rights-
Creosote-Treated Railroad Ties Page 6 of 10

End-of-Life Evaluation February 18, 2010

of-way land, then those ties will decay through aerobic bacterial action on the soil surface.

Complete decomposition is assumed to occur over approximately 40 to over 100 years. In areas

where access is practical, some ties may be reclaimed by residents for landscape or fence uses,

but the ties would still decay in about the same time. Since decay is aerobic, no methane

emissions result.

The used tie wood decays to produce approximately 247 pounds of biogenic carbon dioxide and

the creosote would decay to produce approximately 39 pounds of fossil carbon dioxide. No

fossil fuel offsets would occur.

Comparison to National Energy Use

The GHG and fossil fuel use reductions possible through recycling ties for energy are significant.

In the U.S., the average energy use per capita is approximately 337 MMBTU, of which 286

MMBTU are fossil fuel. Each tie recycled is estimated in this calculation to yield 1.4 MMBTU

of energy. Thus, each tie recycled represents approximately 0.5 percent of the annual U.S. per

capita fossil fuel usage. Furthermore, the average GHG emissions per capita are estimated at

51,600 pounds of CO2-eq. Each tie recycled results in the elimination of approximately 225

pounds of CO2-eq. and represents approximately 0.5 percent of the annual per capita GHG

emissions.

Limitations

This paper presents a simplified analysis of creosote treated tie life cycle and disposal and is not

a Life-Cycle Assessment. The items analyzed and the impact indicators presented were selected

for the purpose of highlighting the differences applicable to the end-of-life options for ties.

Impacts potentially associated with the production and use of creosote or releases of creosote

during the use life are beyond the scope of this paper. Additionally, impacts associated with

transportation of ties to recycle or landfill sites is not included because 1) it is highly variable

depending on tie removal and disposal

locations, 2) is likely to be very similar for

recycle and landfill disposal options, 3) impacts

may be overstated where ties bound for recycle

are transported on the same cars that will be

reloaded with new ties, and 4) the overall

impacts would be minimal.
Creosote-Treated Railroad Ties Page 7 of 10

End-of-Life Evaluation February 18, 2010

Comparison of End-of Life Alternatives

Use of fossil fuel is reduced, or offset, by the amount of fuel value in each tie that is used

beneficially. The amount of fossil fuel saved for each tie recycled, disposed, or abandoned is

shown in Figure 1. The largest fuel savings results from recycling ties to energy production,

since all of the embodied biogenic and fossil energy is beneficially used. Only a small fraction is

beneficially used in landfill disposal and none is recovered when ties are abandoned.

The GHG balance resulting from each end-of-life

alternative is shown in Figure 2. Recycling for

energy results in a decrease in GHG emissions,

because only the fossil (creosote) fraction of ties

burned contributes to GHG while all of the energy

(biogenic and fossil) is used to offset combustion

of fossil fuel. Landfill disposal increases GHG the

most, due to both CO2 and methane releases

resulting from anaerobic decay within the landfill.

For abandoned ties, the fossil (creosote) carbon

fraction of tie mass is converted to fossil CO2.

Releases potentially causing acid precipitation

for each end-of-use alternative are shown in

Figure 3. Recycling ties for energy produces a

negative acidification indicator because

combustion of wood results in lower emissions

of acidifying gases than combustion of coal.

The acidification caused by burning ties is small,

so that when credit for the higher coal emissions

are subtracted, the result is negative. Landfill

disposal results in a negligible increase related to

methane combustion and abandoning ties

has no impact to acidification.

Comparison of all impact indicators for the

full life cycle is shown in Figure 4. Rather

than indicating actual indicator values,

these have been normalized to show the

recycle option as a negative 1, since all
Creosote-Treated Railroad Ties Page 8 of 10

End-of-Life Evaluation February 18, 2010

indicators for this option are negative. Values for disposal in a landfill and abandonment are

relative to the recycle option. While previously shown figures address only emissions that occur

due to the disposal method applied, this figure includes the full life cycle, beginning with

growing the trees. Negative values mean that releases causing the indicator are reduced by

implementing the disposal option. Positive values indicate the disposal method increases the

impact indicator values.

Another way to consider the full life cycle is to consider the flux of GHG interchange with the

atmosphere as depicted in Figure 5. All end-of-life alternatives start with the same GHG values

from tree growth

through the end of tie

use. The flux begins

at negative 260

pounds of CO2-eq. due

to the CO2 removed

from the atmosphere

and stored in the tie

wood and remains

unchanged as tie is

treated. Injection of

creosote does not

result in a change

since it is not released

as CO2 or methane.

During the tie’s use

the GHG value increases by 33 pounds CO2-eq. per tie due to decay (creosote and wood loss)

while in use. Values for the three alternatives diverge at the end-of-life stage. The recycle for

energy and abandon alternatives increase to a positive 61 pounds CO2-eq. per tie as all carbon

remaining in the ties is converted by combustion or decay, respectively, to carbon dioxide. The

landfill option results in less CO2 emissions, but includes methane emissions (with CO2

equivalent at 21 times those of CO2), raising the landfill alternative GHG total to negative 59

pounds CO2-eq. per tie. As a final analysis at the end-of-life, offsets to fossil fuel use are applied

as shown in Figure 5. Abandoned ties have no offset. Recycled ties have a large offset that

brings the final CO2-eq. per tie value to a negative 227 pounds. Landfilled ties have a small

offset, due to methane capture and energy recovery, bringing the final to negative 67 pounds of

CO2-eq. per tie.
Creosote-Treated Railroad Ties Page 9 of 10

End-of-Life Evaluation February 18, 2010

Conclusions

Of the three end-of-life alternatives for creosote-treated railroad ties considered, recycling for

energy recovery provides clear and significant benefits of conserving fossil fuel resources,

reducing greenhouse gas levels in the atmosphere, and reducing emissions that lead to acid

precipitation.

The fuel offset gained by recycling creosote-treated ties for energy recovery is 20 times greater

than energy recovery from landfill disposal.

Offsets result in a significant decrease in GHG emissions when ties are recycled for energy

compared to a slight increase in GHG emissions when landfilled.

If ties are abandoned, no change results to fossil fuel use or acidification and GHG emissions are

increased approximately one-third as much as by landfill disposal.

The GHG and fossil fuel use reductions possible through recycling ties for energy are significant.

Each tie recycled represents approximately 0.5% of the annual U.S. per capita GHG emissions

and fossil fuel usage. Thus, approximately 200 ties recycled for energy offsets the GHG and

fossil fuel impacts of one typical U.S. resident. If all ties replaced annually in the U.S.,

approximately 20 million ties, were recycled for energy, the result would be to offset the GHG

and fossil fuel use equivalent to a city of nearly 100,000 people.
Creosote-Treated Railroad Ties Page 10 of 10

End-of-Life Evaluation February 18, 2010

References

AP-42. AP-42, Section 1.6, Wood Residue Combustion in Boilers

CameoChemicals. Available at: http://cameochemicals.noaa.gov/chris/CCT.pdf

EIA (2007). EIA, 2007. Annual Energy Review 2007. June 2008, Energy Information

Administration, DOE/EIA-0384(2007)

Engineering Toolbox. The Engineering Toolbox at: http://www.engineeringtoolbox.com

EPA (2006). Solid Waste Management and Greenhouse Gases, A Life-Cycle Assessment of

Emissions and Sinks. U. S. EPA. Available at:

http://www.epa.gov/climatechange/wycd/waste/downloads/fullreport.pdf.

FPL Wood Handbook. Forest Products Laboratory Wood Handbook, FPL-GTR-113. Available

at: http://www.fpl.fs.fed.us.

Holtzman (1995). Holtzman, M. I. and Atkins, R. S. Emissions From Combustion of Treated

Wood Fuel and Tires in Industrial Boilers. 88th Annual Meeting of The Air and Waste

Management Association, 1995.

Kohler and Kunniger (2003). Kohler, M. and Kunniger, T., 2003. Emissions of polycyclic

aromatic hydrcarbons (PAH) from creosoted railroad ties and their relevance for life

cycle assesment (LCA). Holz als Roh- und Werkstoff 61 (2003) 117-124.

NREL. National Renewable Energy Laboratory (NREL), detail spreadsheetDSButuminousCombustionUtilityBoilers.xls

TRACI. Tool for the Reduction and Assessment of Chemical and Other Environmental Impacts

(TRACI), U.S. EPA. Database available from Jane Bare at bare.jane@epa.gov.

Zarembski (2007). Zarembski, A.M. and Kondapalli, S., 2007. Development of Comparative

Crosstie Unit Costs and Values. CrossTies. Jan/Feb 2007, pp. 17-18.