West of the Indiana Harbor Belt (IHB) line passing below adjacent to IHB's La Grange location, with North Tilden Avenue on its west side, also below the line, the BNSF Three Main Track line, with speed limit 70-45, continues west-southwest past a bridge over US 34 curving below, a signal bridge (Intermediate Signals, MP 13.6) and grade crossing (US 45), Metra stations at La Grange [Road] (MP 13.7), with streets along both sides (Hillgrove Avenue to the north, Burlington Avenue to the south), followed by two grade crossings (Ashland Avenue, Kensington Avenue), at Stone Avenue [La Grange] (MP 14.1), followed by a grade crossing (North Brainard Avenue), Intermediate Signals (signal bridge) and two more grade crossings (Gilbert Avenue, Well Road), at Western Springs (MP 15.4), which has a grade crossing (Lawn Avenue) within the platforms and a grade crossing (Grand Avenue) at the west end, followed by Intermediate Signals (signal bridge), a pedestrian crossing, a section of embankment with several streets passing below, and a bridge over the I-294 Tollway below, at Highlands (MP 16.3), with a signal bridge, the Oakes Street bridge overhead of the line in a cutting, crossovers, pedestrian crossing, and signal bridge west of the station, at Hinsdale (MP 16.8), which has the North Garfield Avenue grade crossing east of the station, the North Washington Avenue and North Lincoln Avenue grade crossings west of the station, umbrella sheds on the platforms, and a depot on the south side with parking meters on the adjacent streets, including East Chicago Avenue alongside to the south, followed by two grade crossings and a signal bridge, crossovers, and signal bridge at West Hinsdale (MP 17.8) east of the eponymous Metra station, which has a grade crossing within the platforms (South Slough Street) and West Hinsdale Avenue alongside to the south, followed by the SR 83 road bridge overhead and Intermediate Signals (signal bridge).
There are Metra stations at Clarendon Hills (MP 18.2), with parking on the north side of the platforms and southwest of the station, and a grade crossing (Prospect Avenue) at the west end of the station, where the line turns due west, Intermediate Signals (signal bridge, MP 18.7/8), at Westmont (MP 19.4), which has a grade crossing (South Cass Avenue) at the east end of the platforms, with West Quincy Avenue south of the station, and is a mini-summit on the line, followed by Intermediate Signals (signal bridge, "Fairview"), West Burlington Avenue alongside to the north, and a spur on the south side, at Fairview Avenue (MP 20.3), which has a wooden depot on the south side, a grade crossing (Fairview Avenue), signal bridge, crossovers, and signal bridge, and an acute angle grade crossing at Maple Avenue, west of the station, and at Downer's Grove (MP 21.1), which has a grade crossing east of the station (Washington Boulevard), a grade crossing within the station (brick depot to the south), and a grade crossing at the west end (Forest Avenue), with Main Street and extra track alongside to the north, followed by a signal bridge, crossovers, and a signal bridge, before the speed limit rises to 70-50 at MP 21.6. Gilbert Avenue and then Burlington Avenue are alongside to the south and Warren Avenue to the north.
There is a signal bridge, crossovers, a signal bridge, and Metra stations at Belmont (MP 22.6), which has a brick depot to the southeast, set diagonally, with a grade crossing (Belmont Road) at its east end (Underpass being built in April, 2011) and Intermediate Signals (signal bridge, MP 22.8/.9) at its west end, Burlington Avenue is alongside to the north and then Railroad Avenue to the south, and I-355 bridges overhead, and at Lisle (MP 24.4), which has Intermediate Signals at East Lyle, depots and parking lots on both sides of the line, followed by a bridge over North Main Street, a signal bridge, crossovers, and a signal bridge, a bridge over Route 53, and a bridge over a drainage channel. The line turns west-southwest, past a road bridge overhead (Yockley Avenue), trees on both sides of the line, Intermediate Signals (signal bridge), and a housing development on the south side, and then southwest, past a bridge over a road (Naper Boulevard), Intermediate Signals (signal bridge, MP 27.1), detectors at MP 27.2, and trees on the south side of the line, before resuming its westward course past a signal bridge (Intermediate Signals, MP 27.6), a road bridge overhead (North Columbus Street), crossovers, and a signal bridge, and a grade crossing (North Loomis Street) at the east end of the Metra/Amtrak station at Naperville (MP 28.4), which has umbrella sheds on the platforms and a brick depot on the south side with parking lots around it as well as parking on the northwest side, with the Kroehler Manufacturing Company (furniture) along the northeast side of the station (not currently rail-connected), followed by a bridge over North Washington Street, a signal bridge, crossovers (West Naperville), a signal bridge, a bridge over North Main Street, a spur on the south side of the line, a bridge over a river, Intermediate Signals (signal bridge, MP 29.8/.9), a grade crossing (North Rivera Road), a bridge over US 34, and the start of extra tracks on the north side.
The line continues past Intermediate Signals (signal bridge, MP 31.1), extra tracks on the south side serving a lineside industry that uses covered hoppers, a bridge over a stream, Route 59 passing below, the Metra station at Route 59 (MP 31.6), extra tracks on the south side for a rail-served industry, and a signal bridge (MP 32.1) at the end of the extra tracks on the north side, and under the Elgin, Joliet & Eastern's overhead bridge near that line's Eola location, with connectors down to the BNSF main line in the northwest and southwest quadrants.