Implications of policy-driven transmission expansion for costs, emissions and reliability
December 4, 2025
Abstract
The US power system requires substantial transmission expansion to meet long-term demand growth, improve reliability and accommodate more renewable energy. However, interregional transmission deployment has been slow. Multiple congressional proposals aim to address this issue. This study evaluates these proposals through a representative policy-driven expansion methodology requiring regions to interconnect. We assess impacts on transmission builds, cost, reliability during extreme events and emissions. We highlight the difference between policy-driven expansion that pursues expansion in all regions and an expansion focused on capturing the benefits of low-cost generation potential. Policy-driven expansion increases interregional transmission by 68%, distributing expansion across regions, whereas the least-cost solution concentrates builds in the central USA. Although the least-cost approach yields US$1.52 billion (1.13%) greater savings and 28.6 million metric tons (3.65%) lower CO2 emissions, policy-driven expansion improves reliability during extreme events by enabling broader electricity exchange. The study highlights key trade-offs to inform transmission policy decisions.
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Data availability
We provide a supplementary document that discusses additional methods and assumptions and more detailed results on base and sensitivity scenarios. Data necessary to replicate the results in the paper are provided via Github at https://github.com/JRLSenga/Transmission_PolicyImpacts. Source data are provided with this paper.
Code availability
Replication software is provided via Github at https://github.com/JRLSenga/Transmission_PolicyImpacts.
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Acknowledgements
We would like to acknowledge B. Patten, S. Wang, D. Mallapragada, N. Shi, S. Chakraborty and P. Duenas Martinez for insightful discussions on GenX, feedback on the models, assumptions and policy implications. All views expressed in this paper are those of the authors and do not necessarily reflect the views of acknowledged individuals or affiliated institutions.
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Authors and Affiliations
Contributions
Conceptualization: A.B., C.R.K., J.E.P., J.R.L.S. and S.D.S. Methodology: A.B., C.R.K., J.E.P., J.R.L.S. and S.D.S. Software: J.R.L.S. Formal analysis: A.B., C.R.K., J.E.P., J.R.L.S. and S.D.S. Data curation: J.E.P. and J.R.L.S. Writing–original draft: J.R.L.S. Writing–review and editing: A.B., C.R.K. and J.E.P. Visualization: J.R.L.S.
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Extended data
Extended Data Fig. 1 Regional and System CO2 Emissions in the Fixed and Optimal ITC under the Recent Policy Developments scenario.
Solid (dashed) lines represent the Fixed (Optimal) ITC scenarios. The IRA+OSW scenario show the same results as in Fig. 4.
Extended Data Fig. 2 Histogram of Simulated Average Hourly Non-Served Energy per Region.
We show the (a) IRA+OSW and (b) Recent Policy Developments scenarios with a 30% MITC under a Current Policies scenario. Colored values in each graph represent the mean (standard deviation) value for the scenario. Each histogram consists of 1000 data points, where each data point corresponds to a random capacity outage for that region. The y-axis represents the number of simulated outages while the x-axis represents the value of hourly NSE in gigawatt-hours. The dashed lines connect the average NSE under each policy with the average NSE under the status quo, while the percentages indicate the relative change in NSE. Note the different x and y-axis scales per region.
Supplementary information
Supplementary Information
Supplementary Figs. 1–34, discussion, methods and Tables 1–20.
Supplementary Data 1
Contains the data necessary to replicate the figures in the Supplementary Information file.
Source data
Source Data Fig. 1
Existing transmission capacity per line and transmission capacity investments per line per policy and MITC combination.
Source Data Fig. 2
Total system cost per MITC and breakdown per cost component.
Source Data Fig. 3
New capacity investments per region, technology and policy.
Source Data Fig. 4
Total CO2 emissions per region, MITC and policy.
Source Data Fig. 5
Extreme weather event simulated outages per region and policy.
Source Data Fig. 6
a,b, Existing transmission capacity per line and transmission capacity investments per line for the Fully Coordinated scenarios. c, Extreme weather event simulated outages per region and policy in the Fully Coordinated scenarios.
Source Data Fig. 7
a, Total system cost for the IRA+OSW, No IRA with OSW and Recent Policy Development scenarios. b–d, Existing transmission capacity per line and transmission capacity investments per line for the IRA+OSW, No IRA with OSW and Recent Policy Development scenarios. e, New capacity investments per region, technology and policy.
Source Data Extended Data Fig. 1
Total CO2 emissions per region and MITC for the IRA+OSW and Recent Policy Development scenarios.
Source Data Extended Data Fig. 2
Extreme weather event simulated outages per region for the IRA+OSW and Recent Policy Development scenarios.
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Cite this article
Senga, J.R.L., Botterud, A., Parsons, J.E. et al. Implications of policy-driven transmission expansion for costs, emissions and reliability in the USA.
Nat Energy (2025). https://doi.org/10.1038/s41560-025-01921-7
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Received: 03 March 2025
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Accepted: 28 October 2025
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Published: 04 December 2025
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Version of record: 04 December 2025
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DOI: https://doi.org/10.1038/s41560-025-01921-7
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