SPRINGFIELD — Daily passenger train service between the city’s Union Station, Holyoke, Northampton and Greenfield could begin as soon as Aug. 30.

But the start date could be pushed back depending on results of passengerless nighttime test runs Amtrak is making from Springfield to Greenfield along the Knowledge Corridor line this week, according to the Massachusetts Department of Transportation.

Amtrak and MassDOT had planned to begin the service earlier this summer, but it was delayed due to track and signal work in Greenfield, according to MassDOT.

In a statement, Amtrak said it’s running one or two round trips overnight through Friday between 11 p.m. and 5 a.m.

Officials have said the test runs are meant to familiarize staffers with the route and make sure Amtrak’s equipment can operate safely on the line that already hosts Amtrak’s Vermonter long-distance train running from St. Albans, Vermont, to Washington.

Amtrak is warning folks to be aware near rail crossings.

Speeds on the line reach nearly 80 mph on long stretches of straightaway north of Northampton and between Holyoke and Northampton along the river.

The Knowledge Corridor Train, now called the Valley Flyer, will offer two round trips on weekdays -- morning and night -- and one round trip on weekends.

The trains will be a continuation of Amtrak shuttles from Springfield to New Haven, Connecticut, part of the Hartford Line service it has operated with CTrail for 14 months now.

It’s a test program with trains only funded for two years. MassDOT will judge whether to continue depending on how well the train is used.

Gov. Charlie Baker and U.S. Rep. Richard E. Neal, D-Springfield, announced the rail plans last year at a news conference in Union Station. Neal long championed the $108 million rehab of Union Station including $11 million of platform and elevator work for Platform C that will make it accessible to those with physical handicaps.

That means the new Amtrak service as far north as Greenfield will connect with Amtrak and Metro-North trains to New York City.

In January 2010, Massachusetts was awarded $70 million in federal stimulus funds for design and construction of the Knowledge Corridor along the Connecticut River. Track restoration began in 2013 and was completed in late 2014. Amtrak’s Vermonter service was rerouted onto this shorter and faster line, avoiding a turnaround in Palmer.

Tickets for expanded Knowledge Corridor/Valley Flyer service are not yet available on Amtrak’s website.