The magic number for the Washington Nationals to clinch the eastern division is four. But for weekend Metro riders, we now have a magic number of two: Metrorail has decided to cancel the major track work it had planned for the first two weekends in October.

The cancellations were at least in part because of the potential for higher ridership during playoff season. The first weekend in October also includes the Columbus Day holiday. For several years, Metro has been scheduling major track programs for many three-day weekends, but riders have complained that some of those long weekends — especially the Mondays — are busier than others.

Metro canceled station shutdowns originally scheduled for the Labor Day weekend and has now done the same for the Columbus Day weekend.

The original schedule for Oct. 6-8 would have closed five stations on the east side of the Blue and Orange lines as well as Takoma on the Red Line. The original schedule for the following weekend would have closed McPherson Square, Metro Center and Federal Triangle on the Blue and Orange lines.

Major track work still is scheduled for the Red and Orange lines on the weekend of Oct. 20-21. (And remember, we’re talking throughout this posting about what Metro defines as major track work, meaning the spliting of lines and the closing of stations. Metro hasn’t announced a final schedule for work that involves trains sharing tracks around work zones, although spokesman Dan Stessel says Metro will be “sensitive to customer experience” in October.)

The Nats’ impact on Metro weekend service in October is impossible to predict. Some scenarios may appear more likely than others — especially to ardent fans — but the team’s fortunes and the timing of games are in flux.

Division Series are scheduled to begin Saturday, Oct. 6. The National League Championship Series is scheduled to begin Sunday, Oct. 14. The World Series is scheduled to begin Wednesday, Oct. 24.

My colleague, Mark Berman, plans to write more about other transit issues related to the playoff picture, including whether someone will pay to keep Metrorail running past its normal bedtime if a game goes late.

Meanwhile, there’s plenty of track work of all sorts coming up this weekend. All the work disruptions are scheduled to begin at 10 p.m. Friday and continue through Metrorail’s midnight closing Sunday. (The Nats, Redskins and D.C. United are not at home this weekend.)

Green Line: Free shuttle buses will replace trains between Southern Avenue and Branch Avenue. Branch Avenue, Suitland and Naylor Road stations will be closed.

Using the shuttles will add about 40 minutes to normal travel times, Metro says. Between Southern Avenue and Greenbelt, trains will be on their regular weekend schedule.

Orange Line: Free shuttle buses will replace trains between Vienna and East Falls Church. Trains will operate between East Falls Church and New Carrollton about every 16 minutes.

Express buses will operate between Vienna and East Falls Church only. A local route will include stops at Dunn Loring and West Falls Church. The express route should add about 15 minutes of extra travel time. Taking the local route for the full trip would add about 40 minutes.

Red Line: Trains will share a track between NoMa-Gallaudet U and Fort Totten. They will operate every 20 minutes between Shady Grove and Glenmont. Between 9 a.m. and 9 p.m. Saturday and Sunday, more trains will operate between Shady Grove and NoMa-Gallaudet U. So in that zone, trains should reach platforms about every 10 minutes, Metro says.

Riders on the eastern side of the line, where the work is, should add about 15 minutes of extra travel time. (Some riders might want to transfer to the Green Line at Fort Totten to reach downtown stations.)

Yellow Line: Trains will share a track between Huntington and Braddock Road. They will operate between Huntington and Mount Vernon Square about every 16 minutes. They won’t go north of Mount Vernon Square this weekend, so to continue your trip, switch to the Green Line.

To get through the work zone, add about 10 minutes to normal travel times.

Blue Line:There’s no track work scheduled, but the train schedule is a bit different. The trains will operate about every 16 minutes between Franconia-Springfield and Largo Town Center to avoid schedule conflicts with Orange and Yellow Line trains, Metro says.