Adding toll lanes to Interstate 270 and most of the Capital Beltway in Maryland could require a government subsidy of $482 million to $1 billion even as state officials have said the highway expansion would come at “no net cost” to taxpayers, according to a study of the proposal released Friday.

Whether the state would have to pay that subsidy depends on how toll revenue stacks up against construction and borrowing costs, as well as the costs of operating and maintaining the lanes, according to the draft environmental impact study unveiled by the Maryland Department of Transportation (MDOT).

A government subsidy would be required if those costs turned out to be on the higher end of the range. If costs are on the low end and revenue on the high end, the lanes could produce a windfall of up to $2.7 billion, the study found.

Maryland Gov. Larry Hogan (R) has said the highway expansion will come at no cost to taxpayers because teams of private companies will design, build and operate the lanes — and pay for their construction — in exchange for keeping most of the toll revenue long-term.

State transportation officials have previously said the state might have to subsidize some construction because parts of the highway system would generate more toll revenue than others, but the study revealed the first hard numbers. Maryland officials also said the state could use revenue from the more lucrative sections to subsidize those that would come up short.

The financial estimates in the study cover the entire 48-mile highway system, so it is unclear whether construction could be sequenced to minimize the need for government funding.

The study found that the two toll-lane options that would provide the greatest traffic relief would cost $8.7 billion to $10 billion to build. It also said the state’s “goal” is that the lanes come at “no net cost to the state” and with “limited or no government funding upfront.”

MDOT declined repeated requests for interviews to discuss the study and its new financial analysis.

In an email, Maryland Transportation Secretary Gregory Slater said the study shows a range of “cashflow estimates” because the lanes will be built over several years, with construction and financing costs varying throughout.

Slater said the state will “work through the market conditions at each phase to make sure that we are maximizing the value to Maryland.”

A Hogan spokesman did not respond to a request for comment.

The numbers jumped out to critics of the governor’s toll-lanes plan.

“The whole promise we’ve heard was that no taxpayer subsidy would be needed, and that keeps getting walked back,” said Ben Ross, chair of the Maryland Transit Opportunities Coalition.

The 350-page analysis, which balloons to 18,000 pages with technical reports, repeats much of what the state previously released in spring 2019 as part of a multiyear environmental review.

The two alternatives projected to provide the most traffic relief would require destroying 34 homes and four businesses, mostly near the Beltway in Forest Glen and Silver Spring in Maryland’s Montgomery County. Construction would “directly” affect about 1,500 properties in both Montgomery and Prince George’s counties, require cutting about 1,500 acres of forest, and affect 47 local parks, the analysis found.

Such federally required studies provide residents and property owners a sense of whose homes or property could be affected and who will hear more highway noise or breathe more traffic fumes under options being considered. They also typically form the basis of any lawsuits by opponents trying to slow down, change or stop major transportation projects.

The two options that would reduce traffic congestion most would have four toll lanes — two in each direction — on both the Beltway and I-270. In one scenario, I-270 would see two new toll lanes constructed to serve traffic flowing in each direction, in addition to its existing carpool lanes. In the other, one new toll lane would be constructed in each direction, and the existing carpool lanes would be converted to toll lanes.

As in Northern Virginia, the new lanes would allow motorists to buy their way out of congestion. The toll price would vary to keep traffic in those lanes moving at a minimum speed of 45 mph. The regular traffic lanes would be rebuilt but remain free. The study cites 2025 as the “estimated opening year.”

The two-year study covered the Beltway from the George Washington Parkway in Northern Virginia to Route 5 in Prince George’s County, Md. It also included I-270 between the Beltway and I-370.

However, state officials have said they will first seek to add the lanes to the Beltway between Virginia and the western spur of I-270, as well as the lower portion of I-270 from the Beltway to I-370. That work will include replacing the 58-year-old American Legion Bridge with an expanded structure, potentially with a new bicycle and pedestrian path on the new bridge’s south side.

Maryland officials recently postponed plans to add Beltway toll lanes east of I-270 because of the greater impacts on parkland and neighborhoods, but the environmental analysis covered the entire Beltway.

By 2040, the study found, speeds in both highways’ regular lanes would average 40 mph if toll lanes are built under the two proposals that offer the biggest traffic improvements. That compares with 25 mph if no lanes are added. All of the alternatives under consideration would reduce delays by at least 22 percent, the study found.

Hogan and project supporters have said Maryland needs to reduce traffic congestion that they view as harming quality of life and stifling economic growth. Critics have said that expanding highways encourages driving and that toll lanes are unfair to lower-income motorists.

Ross, the transit advocate, spotted in the report what he called “the I-270 coverup.” Tucked into a technical report is a chart showing that afternoon traffic heading north on I-270 in the regular lanes would become slower between the Beltway and I-370 after toll lanes are built.

Without toll lanes, that trip is projected to take 10 minutes during the afternoon rush, the study found. With the additional lanes, it is estimated to take 12 to 16 minutes. That is likely because adding the toll lanes south of Shady Grove first will require even more lanes to funnel into the two lanes north of that area, where traffic already backs up daily, until the entire highway is widened.

“They were clearly doing their best to bury that,” Ross said.

MDOT officials did not respond to questions about the I-270 traffic analysis.

Forty-four environmental and community groups, as well as members of Maryland’s congressional delegation, have asked federal and state highway officials to extend the 90-day comment period for the study to 120 days because of the scope of the proposal and the disruptive effect of the coronavirus pandemic. However, state officials said Friday that the public comment deadline remains Oct. 8.

State officials will then choose a “preferred alternative” to submit for federal approval as they solicit companies for the public-private partnerships.

Comments on the study can be made via MLS-NEPA-P3@mdot.maryland.gov. Two in-person public hearings and four virtual public hearings are scheduled for late August and early September.