Caltrain Electrification Project

Martin Gonzalez
November 21, 2023

Submitted as coursework for PH240, Stanford University, Fall 2023

Introduction

Fig. 1: Map of Caltrain rail service from San Francisco to Gilroy. (Source: Wikimedia Commons)

Commuter rail is a public transportation service that offers transit via railroad locomotives. These railroad services connect metropolitan areas to their respective suburbs; but may also feature extended lines that connect different urban centers. Commuter rail can offset the emission of greenhouse gasses (GHGs) by displacing emissions that would otherwise be the result of automobile transportation. For example, CalTrain is the commuter rail serving the peninsular San Francisco Bay Area along a 77-mile stretch connecting San Francisco to San Jose to Gilroy, as shown in Fig. 1. In 2020, CalTrain emitted 40,411 metric tons of carbon dioxide equivalent (MTCO₂e), while burning 3.8 million gallons of diesel fuel to power its fleet of locomotives. [1] However CalTrain has engaged in a modernization project to transition a majority of its diesel trains into an electrified fleet beginning in 2024. Caltrain will run a mixed fleet of approximately 75% electric trains and 25% diesel trains, with full conversion to occur at a future time when funding is identified. [2]

Caltrain Scope 1 GHG Emissions

The Caltrain fleet of locomotives is powered by the burning of diesel fuel, the rail's largest contribution to GHG emissions. Diesel is composed of 75% saturated hydrocarbons and 25% aromatic hydrocarbons, with an average chemical formula of C₁₂H₂₃ and a density of 0.85 kg/liter. [3] Hydrocarbons have an energy density (by weight) of 4.42 × 10⁷ J kg^-1, allowing us to calculate Caltrain's annual energy budget for operating its fleet of diesel locomotives. Here we show a sample calculation of the conversion between gallons of diesel usage in 2016 and its equivalent energy usage, based on data provided by Caltrain 2021 Sustainability Report. [1]

4.5 × 10⁶ gals × 3.8 L gal^-1 × 0.84 kg L^-1

× 4.2 × 10⁷ J kg^-1 = 6.34 × 10¹⁴ J (176,000 MWh)

The total annual energy usage over the period 2016-2020 has steadily declined; associated with a decline in operating train miles in response to decreased ridership. However, the energy-usage per mile remained relatively constant between 4.25 × 10⁸ - 4.5 × 10⁸ J mile^-1 (or 3 - 3.25 gallons per mile). The total energy required to power the diesel fleet should be roughly equivalent to the electrical energy needed to power the electrified fleet. Therefore, we must investigate the source of electrical power to determine the true extent to which greenhouse gas emissions are being reduced because of the Caltrain electrification project.

Type of Fleet	Scope 1 Emissions (MTCO₂e)
All-Diesel	42821
Mixed Fleet	10705

Table 1: Estimated Scope 1 GHG Emissions for Caltrain's all-disel andmixed fleet given future energy demand predictions. Figures estimated using projections from Caltrain Energy Procurement Strategy Report. [4]

In discussing the effect of Caltrain electrification on GHG emissions, we must first distinguish between different definitions of emissions. Scope 1 emissions refers to emissions from sources that the organization owns or controls directly. For Caltrain, this refers to emissions produced by the burning of diesel to power their locomotives. Scope 2 emissions are indirect emissions that occur through the use of purchased electricity and originate from the site of power generation and subsequently distributed to the end user. [4] For Caltrain, this refers to emissions produced by power suppliers that produce electricity that will directly power the new electrified trains. The transition to a mixed electrified/diesel fleet will clearly result in a reduction in Scope 1 emissions, because the use of electrified trains will displace emissions that would previously result from burning diesel.

Here we present a calculation of the estimated Scope 1 emissions resulting from Caltrains transition to a mixed electrified/diesel fleet. We expect some reduction in direct emission from the replacement of diesel fuel to electrified power. Caltrains mixed fleet of 75% electrified trains and 25% diesel trains will require a projected energy demand of approximately 159,000 MWh per year. Approximately 119,000 MWh will be supplied as electricity for its electrified trains, and the remaining 40,000 MWh will require an equivalent volume of diesel for its existing non-electric trains. [5] To make a comparison on total Scope 1 GHG emissions between an all-diesel fleet and a mixed fleet we will make two calculations: 1) an estimate of GHG emissions assuming a continuation of an all-diesel fleet and 2) an estimate of GHG emissions assuming a mixed fleet. For the all-diesel case we have

159000 MWh × 3.6 × 10⁹ J MWh^-1 × 2.38 × 10^-8 kg J^-1

× 0.00316 MTCO₂e kg^-1; = 42821 MTCO₂e (all-diesel fleet)

For this calculation, used the average chemical formula for diesel (as presented above) to determine that 0.00316 MTCO₂e per kg of burned diesel. Given this conversion, we determined the total mass of diesel required to meet the projected energy demand. Based on this estimate, we conclude that approximately 4.2 million gallons of diesel would be required to meet the energy demand for Caltrain's mixed fleet. Note that the estimated required diesel volume and its associated GHG emissions are slightly higher than the figures reported in the Caltrain 2021 sustainability report. This increase may be explained by Caltrain's plans to increase service frequency from four to seven trains per peak hour per north-south direction. [2] Hence, assuming Caltrain were to continue to use an all-diesel fleet we would expect GHG emissions to rise. However, Caltrain is set to transition to a mixed fleet, with a large chuck of its Scope 1 emissions displaced by electrified trains. Hence the Scope 1 emissions from the mixed fleet follows the previous calculation, but here we start with the 40,000 MWh of energy that will continue to require diesel. For the mixed fleet we thus have

40,000 MWh × 3.6 × 10⁹ J MWh^-1 × 2.38 × 10^-8 kg J^-1

× 0.00316 MTCO₂e kg^-1; = 10705 MTCO₂e (mixed fleet)

As expected, Scope 1 Emissions is significantly reduced when compared to the case of the all-diesel fleet. This estimate corresponds to a little less than 1.1 million gallons, consistent with Caltrain's mixed fleet being composed of 25% diesel trains. Therefore, Caltrain's transition represents an improvement on Scope 1 emissions. However, emissions displaced by electrified trains will still be emitted by the source generating electrical power for the mixed fleet. These emissions constitute Scope 2 emissions. We will now discuss how Caltrain electrification will affect their Scope 2 emissions.

Caltrain Scope 2 GHG Emissions

Caltrain's Scope 2 emissions are much less straightforward to calculate because of the difficulty in tracing the physical origin of the electrical power that powers the mixed fleet. In Caltrain's Energy Procurement Strategy, Caltrain claims to purchase 100% of its electrical power from renewable sources via various Community Choice Aggregation (CCA) programs. [4] CCAs offer an alternative to investor-owned utility suppliers whereby local governments aggregate purchasing power to procure energy on behalf of its constituents. As required by the California Energy Commission's Power Source Disclosure Program, electricity suppliers must put out a Power Content Label (PCL) that disclose their procured energy sources and associated GHG emissions. The CCAs that serve Caltrain all report services with 100% non-GHG emitting power sources; notably wind, solar, and hydropower. With this reporting, Caltrain makes its claim that since its purchases of electrical power come from non-carbon sources; their indirect emissions are eliminated. However electricity delivery is handled by Pacific Gas and Electric (PG&E) vast transmission and distribution network; whose electricity may come from either carbon-neutral or fossil fuel sources. Notably, the Metcalf Energy Center located south of San Jose is a natural gas fired power plant that provides electricity to many residents of the South Bay Area. Furthermore the CCA's procures its power from renewable sources which may be distant from the Bay Area. As an example, Peninsula Clean Energy (PCE) reported in their 2018 Integrated Resource Plan purchase agreements with Cuyama photovoltaic facility in Santa Barbara, CA. [6] While Caltrain may claim to purchase electricity from exclusively renewable sources, the reality of its direct electricity supply is shrouded in mystery.

Due to the difficulty of quantifying the proportions of electricity that comes from carbon-neutral and fossil fuel sources, the best we can accomplish an upper bound on Scope 2 emissions from electricity generation. This upper limit assumes that all electricity is generated from natural gas combustion. This assumption is supported by PG&E's power content label which indicates that California's power mix constitutes natural gas as the majority fossil fuel electricity source. [7]

Natural gas is mostly composed of methane with trace amount of other hydrocarbons (ethane, propane, etc). Given the compositional mix of natural, we establish emissions of 0.00272 MTCO₂e per kg of natural gas combusted. [8]

119000 MWh × 3.6 × 10⁹ J MWh^-1 × 2.38 × 10^-8 kg J^-1

× 0.00272 MTCO₂e kg^-1; = 27540 MTCO₂e (electrified trains only)

The upper-bound on Scope 2 emissions from a mixed fleet with electrified trains powered solely by natural gas combustion is 27540 MTCO₂e. The actual value for GHG emissions depends on the relative mix of carbon-neutral and fossil fuel sources that provide electrical power to these trains. We see that while direct Scope 1 emissions are significantly displaced by Caltrain electrification; in reality they continue to be emitted in the form of indirect Scope 2 emissions from electricity generation. Numerically, emissions from natural gas is still an improvement over diesel combustion. However, the true reduction in total emissions (Scope 1 and 2) will depend on how much electricity comes from non-carbon sources.

Electrified Trains - A Bigger Picture

Fig. 2: Passenger train along the NEC operated by Amtrak. (Source: Wikimedia Commons)

While CalTrain's adoption of an electrified fleet nearly eliminates their greenhouse gas emissions; this reduction represents a tiny fraction in comparison to emissions from single passenger automobiles. Substantial reductions in GHG emissions from commuter trains are only possible if there is mass adoption of electrified rail and a large shift towards commuter rail in place of automobiles. Apart from Caltrain's transition to electrified rail, the only other electrified inter-city commuter rail services in the United States are the Northeast Corridor (NEC) and the Keystone Corridor, both of which are operated by Amtrak. The NEC is more expansive than Caltrain, as it connects Washington D.C to Boston and services freight trains. The NEC is the busiest passenger rail line as measured by total ridership and frequency of trains. [9] A train along the NEC is shown in Fig. 2. Given the low level of commuter ridership in the United States, a bigger reduction in GHG emissions may be possible when including freight rail into the electrification project. Nevertheless, the Caltrain electrification project provides a glimpse of the possible environmental impacts of using fossil fuels to power locomotives.

© Martin Gonzalez. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.