HARTFORD, Conn. — Northeast Utilities and Spectra Energy Corp. have announced plans to expand natural gas access to New England and end bottlenecks that have driven up prices when demand spikes in the winter.

The companies said Tuesday the $3 billion project expanding a network of pipelines is expected to begin operating in November 2018.

The project will rely on routes already used to minimize the impact of construction on communities, landowners and the environment.

NU and Spectra say that in the past 15 years, natural gas-fired generation has grown from serving 15 percent of New England’s annual electric requirements to about half.

Gas demand for heating customers rose significantly last winter, leaving less gas available for electric generation. Older coal and oil plants were called in, driving up prices and adding to pollution.