WALKING BACK A POSITION she took in early 2017, Transportation Secretary Stephanie Pollack said on Monday that it may be necessary to extend the contract with Keolis Commuter Services for two years to give the MBTA time to launch a major overhaul of commuter rail services in Massachusetts.

Momentum seems to be building for a dramatic rethinking of commuter rail service, moving to a system with more frequent all-day service. State transportation officials have modeled six alternatives, with capital costs ranging from $1.7 billion for a slight upgrade over existing service to $28.9 billion for a subway-like operation with electrified trains running every 15 minutes everywhere on the system.

Joe Aiello, the chair of the Fiscal and Management Control Board, said a stakeholder group and the public will weigh in on the alternatives in October and the board will try to reach some consensus on which approach to pursue at a meeting in November.

The current contract with Keolis expires in 2022, and most analysts believe it will be impossible to frame a contract for a major overhaul of the system by then. Pollack, who in early 2017 vowed not to renew the contract with Keolis because of a desire for a fresh restart amid concerns about the company’s poor performance, had hinted earlier this year she might need to extend the existing contract.

On Monday, Pollack made it official. After a meeting of the Fiscal and Management Control Board on Monday, Pollack said the procurement of a next generation commuter rail service, with pilot projects, electrification, and the purchase of a new fleet, would take considerable time to put together.

“That’s probably going to take a little longer and we might have to look at exercising one of the extensions that is built into the contract” with Keolis, Pollack said.

Tory Mazzola, a spokesman for Keolis, issued a statement saying the company is interested in serving the Massachusetts market in whatever capacity is needed. “We’re committed to Boston for the long-term to continue making progress in service reliability, modernizing the commuter rail organization and investing into our workforce, all in partnership with the administration,” the statement said. “Whether it is for the remainder of this contract or in future proposals to advance the MBTA’s Rail Vision, we will continue to draw from our global expertise and local knowledge for the betterment of the Commonwealth and our passengers.

Rep. William Straus, the House chair of the Legislature’s Transportation Committee, in the past has raised concerns about extending the Keolis contract.  It’s unclear whether he would be swayed by the circumstances Pollack is confronting.

Pollack’s decision is also made easier by the fact that Keolis’s performance has steadily improved over the last several years.

The rethinking of commuter rail service would be a huge shift for the MBTA. The current service is designed for people commuting back and forth between the suburbs. State transportation officials are now envisioning more frequent service moving in both directions.

The options under study range from the most basic – service every 30 minutes at peak periods to every hour off-peak — to the most radical – service every 15 minutes everywhere on the system. In between those two extremes, there are proposals calling for service every 15 minutes to select key stations or stations within the urban core. There are also proposals to elevate station platforms so passengers could board and off-load more quickly, and initiatives to electrify all or part of the system. Some options call for expanding South Station while others propose building an underground rail link between North and South stations.

Computer modeling of the various options shows how ridership would be affected. According to the model, ridership would increase with frequency of service. For example, the lowest level of train frequency (every 30 minutes at peak and every 60 minutes off-peak) would boost ridership 19,000 riders daily by 2040 compared to making no change in the system at all. By contrast, providing 15 minute service between urban stations would boost traffic by just over 80,000 riders, while adding 15 minute service on the entire system would add 225,900 riders.

Pollack said the research indicates more frequent service is what attracts riders. System electrification has a minor impact on ridership, but she said it may still be warranted if it significantly reduces greenhouse gas emissions.