When people talk about the energy transition in the United States, one challenge comes up repeatedly. We need more transmission.

Transmission lines are the backbone of the electric grid. They allow new renewable generation to connect, support growing electricity demand, and move power across regions. But despite widespread agreement that transmission expansion is essential, new projects often take far longer to complete than originally planned.

I wanted to understand just how common and how long those delays actually are.

Measuring transmission project delays

Rather than focusing on proposed projects or theoretical timelines, I decided to look at something more concrete: transmission projects that have already been built.

Using the Federal Energy Regulatory Commission’s monthly Energy Infrastructure Update reports, I compiled a dataset of electric transmission projects that were placed into service between 2020 and 2025. After filtering for projects longer than 10 miles (where reliable schedule data was available) I ended up with 100 completed projects representing 2,445.7 miles of new transmission infrastructure.

For each project, I compared two things:

• The original in-service estimate published in planning documents such as Certificates of Convenience and Necessity (CCNs) or transmission expansion plans
• The actual completion date reported by FERC

The difference between those two dates shows how much projects slipped relative to their original schedules.

What I found

The results confirmed what is already largely understood. Transmission delays are not the exception, they’re the norm.

More than half of the projects in the dataset (55.6%) were completed later than their originally estimated in-service dates.

Across all delayed projects, the average delay was about 16.4 months.

When projects slipped, they rarely slipped by just a few months:

• 32% were delayed by less than 6 months
• 16% were delayed by 6–12 months
• 52% were delayed by more than a year

Why delays matter

Transmission delays are often discussed in the context of cost overruns. But the consequences extend far beyond individual project budgets.

Transmission infrastructure sits upstream of many other parts of the energy system. When transmission projects are delayed, the impacts cascade outward.

Renewable generation projects wait longer to interconnect.
Large new electricity loads face longer timelines to secure grid access.
And broader goals around reliability and decarbonization move further into the future.

In that sense, transmission delays don’t just affect individual infrastructure projects, they amplify existing bottlenecks across the entire power sector.

If the U.S. hopes to build transmission fast enough to meet growing electricity demand and decarbonization targets, improving project delivery timelines will be just as important as the planning itself.

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