A map of where work on the future Loudoun Gateway station will be done. (Dulles Metrorail Project office)

Given Metro’s troubles with maintaining its current system, you can be forgiven if you forgot that a new addition is under construction.

Heavy construction of second phase of the Silver Line has been going since 2014. Now folks who drive along the Dulles Greenway can see real evidence of that.

Starting this week and continuing through the summer, crews are doing site clearing and excavation work for what will be the Loudoun Gateway station, which will be located in the median of the Dulles Greenway. The station will be located west of the Old Ox Road overpass.

The work means that motorists can expect to see large, slow-moving vehicles and equipment along the roadway. There also may be lane and shoulder closures as construction progresses. Officials are asking motorists to be patient and also to slow down and be careful.

The second phase of the Silver Line will add more than 11 miles to Metro’s existing system and will for the first time, provide a rail link between downtown D.C. and Washington Dulles International Airport. There will be six stations, including two in Loudoun County. The $5.8-billion extension, which is 13-months behind schedule, is expected to open in 2020. While the line will be operated by Metro once it opens, its construction is being managed by the Metropolitan Washington Airports Authority.

The first phase of the Silver Line opened in July 2014. It included five stations — four in Tysons Corner and one in Reston. Metro had high hopes for the rail line, but ridership has been below early projections. The Silver Line also has been blamed for slowdowns in the system, particularly on the Orange and Blue lines.