Over the last two decades, New York has had a difficult time upgrading its ancient signal system, some of which was built before World War II. Only one line — the L train — has modern signals. Work on the No. 7 line has been delayed several times. At the current pace, modernizing the entire system could take a half-century.

Mr. Byford said he could upgrade most of the signal system in the next ten years, which would improve reliability and allow more trains to run closer together. Transit advocates quickly praised Mr. Byford as the right person to shake up a transit agency that is resistant to change.

Mr. Byford has offered an overview about how he would accelerate the signal work. Instead of upgrading one line at a time, he proposed tackling several lines at the same time, including the heavily traveled Lexington Avenue line. He warned that construction work would be disruptive in a way that New Yorkers had never seen before.

On a line that is being converted, stations would be closed during most nights and weekends for two and a half years, Mr. Byford said in an interview. Exceptions could be made for major events like the Fourth of July.

“We’d be sensible about it,” Mr. Byford said. “But this does require New Yorkers’ patience.”

While the station closings will be a hardship, especially for people who work nights and weekends, transit advocates argue that ridership is low at night — only 1.5 percent of weekday riders, or about 85,000 people, use the subway between 12:30 a.m. and 5 a.m. — and that weekend service is already unreliable.

Mr. Byford said he wants to use simple, “off-the-shelf” products that could be installed quickly, instead of being custom-made, following the example of other cities like Shanghai. In New York, only two companies — Thales and Siemens — are allowed to install the new signal system, which is known as communications-based train control. Mr. Byford wants to open the market to more competition.