The O’Hare Flyer and the Threat to Thatcher Woods

Why the route through River Forest doesn’t just pass near a nature preserve — it cuts through one.

Most of the discussion about the O’Hare Flyer has focused on the residential blocks it would run through. But the route also runs directly through Thatcher Woods, a 245-acre Cook County forest preserve along the Des Plaines River, and that piece of the project deserves its own attention — both for what it would do to the preserve and because it opens a separate legal front that has nothing to do with zoning or Village ordinances.

The route doesn’t skirt the preserve. It cuts through the middle of it.

The existing rail corridor runs diagonally through Thatcher Woods, between the Des Plaines River and Thatcher Avenue, passing close to the preserve’s trails, its picnic groves, and the effigy-mound site marked on maps as Serpent Mound. This is the dormant Canadian National line the company has described as part of its route.1

It is not simply a matter of running new trains on old track. On September 4 the company’s chief engineer said the Flyer would build its own separate track within the Canadian National right-of-way, while a remaining freight track serves the line’s few customers overnight.2 Through the preserve, that means new construction along a corridor that today carries almost nothing: clearing, grading, a new track, and — because the existing river crossing is a single-track bridge — a question the company has not answered about how it crosses the Des Plaines. What follows is a passenger train every fifteen minutes in each direction, 4 a.m. to 10 p.m., plus overnight freight, through a designated natural area.

Nothing in the company’s public materials says how the segment through the preserve would be treated. Its only published mitigation — a 15-foot embankment topped by a sound wall and fence — was described for the residential blocks of River Forest, not for the woods.2

What’s actually in the preserve

Thatcher Woods is 245 acres of floodplain forest, savanna, and prairie along the Des Plaines River, and it is not an ordinary patch of trees. The Forest Preserves describe it as “one of the only remaining examples of quality floodplain forest left in the Northeastern Morainal Division of Illinois,” home to more than 250 native plant species and at least 45 nesting bird species, among them wood thrush, ovenbird, scarlet tanager, wood duck, and broad-winged hawk. Egrets, painted turtles, and kingfishers feed in the seasonal floods; pileated woodpeckers work the canopy. A network of trails connects the preserve to the Trailside Museum of Natural History across Chicago Avenue.1

Part of the preserve is formally recognized on the Illinois Natural Areas Inventory, the state’s official register of the highest-quality remaining natural land. Thatcher Woods Prairie is INAI site #1431, listed in Category II — the category reserved for “specific suitable habitat for state-listed species.”3 That designation is not a technicality. It is the same list the state uses to decide which sites require review when a construction project comes through, and it is why this piece of the route is legally different from the rest.

What near-constant train noise does to a forest preserve

Counting both directions, the company’s schedule means a train through the preserve about every seven and a half minutes, eighteen hours a day. The company calls its trains “whisper quiet” and compares them to an electric car.2 That comparison describes motor noise, which matters at low speed. At the 80 mph average the company projects — and the 110 mph it plans elsewhere on the route — a train’s noise comes from its wheels on the rail and from the air it moves, whatever powers it. The company’s own decision to specify a sound wall for River Forest is an acknowledgment of that. Overnight, the freight locomotives serving the line’s remaining customers are governed by a federal standard that permits 90 decibels at 100 feet for a moving locomotive.4

Two decades of research on wildlife and transportation noise point the same direction: sustained noise interferes with birds’ ability to hear the songs they use to hold territory and attract mates, reduces nesting density for a real distance from the source, and can push sensitive species out of otherwise suitable habitat.5 A preserve that exists because it is one of the last quality floodplain forests in its region is precisely the kind of place where that matters.

There is a physical dimension too. Construction of a new track would mean clearing vegetation along the right-of-way through a designated natural area, and any embankment or barrier structure through the woods would cut across a corridor wildlife uses to move along the river. None of this has been addressed in any public material the company has released.

The regulatory angle: why this matters legally, not just emotionally

Because Thatcher Woods Prairie is on the Illinois Natural Areas Inventory, any state or local government action affecting it is subject to a review that does not apply to the rest of the route. Two statutes control: the Illinois Endangered Species Protection Act (520 ILCS 10/11) and the Illinois Natural Areas Preservation Act (525 ILCS 30/17), implemented through 17 Ill. Adm. Code Part 1075.6 Under that rule, state agencies and local governments must evaluate, through formal consultation with the Illinois Department of Natural Resources, whether any construction or other activity they authorize, fund, or carry out is likely to harm a listed species, its habitat, or a Natural Area. The rule is explicit: “The proposed action shall not commence until the completion of the consultation process,” and the agency’s report to IDNR must be filed “prior to approval of … permit, plan, or project approval.”6

That matters here because the company has said it needs the Illinois Commerce Commission to authorize grade separations and crossing changes along the route, including at Thatcher Avenue at the preserve’s edge.2 An ICC order authorizing that work is exactly the kind of state agency action the consultation requirement is built for. It doesn’t guarantee the project gets blocked, and it doesn’t reach the purely residential blocks elsewhere on the route. But it means the segment through Thatcher Woods cannot simply be waved through once an ICC docket opens. The impact on a listed natural area has to be documented and reviewed by the state’s own biologists first — the ICC docket is a public proceeding, and Part 1075 itself provides for public involvement.7

What you can do

  • Watch for the Illinois Commerce Commission docket on the Thatcher Avenue crossing and the other crossings on the route, and file public comment when it opens — specifically raising the Natural Areas Inventory listing of Thatcher Woods Prairie (INAI #1431). We will post the docket number here when it appears.
  • Contact the Forest Preserves of Cook County, which manages Thatcher Woods, and ask what position the District is taking on a passenger-and-freight corridor built through a designated natural area under its stewardship.
  • Raise this with the Illinois Department of Natural Resources directly. The consultation is a separate process from anything the Village of River Forest controls, and it needs its own record of public concern.
  • Share this. Most people following the project have no idea the route runs through a state-recognized natural area, not just a residential neighborhood.
  1. Forest Preserves of Cook County, Thatcher Woods — acreage, habitat, species, and trail details. ↩
  2. High Speed Rail Alliance webinar with O’Hare Flyer CEO Dave Lundy and Chief Engineering Officer Mark Walbrun, September 4, 2026 (transcript on file with ordflyer.com) — separate dedicated track within the CN right-of-way; overnight freight; River Forest embankment and sound wall; “whisper quiet”; ICC grade-separation plans. ↩
  3. Illinois Department of Natural Resources, Illinois Natural Areas Inventory sites by county (November 20, 2024), Cook County: “1431 Thatcher Woods Prairie, II.” Category II is defined on the same list as “specific suitable habitat for state-listed species or state-listed species relocations.” ↩
  4. 40 C.F.R. Part 201, Noise Emission Standards for Transportation Equipment; Interstate Rail Carriers — §201.12 (moving locomotives). ↩
  5. G. Shannon et al., “A synthesis of two decades of research documenting the effects of noise on wildlife,” Biological Reviews 91 (2016): 982–1005. ↩
  6. 17 Ill. Adm. Code Part 1075, Consultation Procedures for Assessing Impacts of Agency Actions on Endangered and Threatened Species and Natural Areas, §§1075.30 and 1075.40, implementing 520 ILCS 10/11 and 525 ILCS 30/17. ↩
  7. 17 Ill. Adm. Code §1075.70, Public Involvement. ↩