Call it the mystery of the missing transit. One of the state’s biggest transit projects, in the works for nearly a decade, was canceled overnight and no one will explain why, or even claim responsibility for the decision.

Two weeks ago, each of the four alternatives for replacing the Tappan Zee Bridge included a new Metro-North commuter rail line and some form of bus rapid transit. The design, which widened the highway but also included a major expansion of transit in Rockland and Westchester counties, was the product of nine years of study and a whopping 280 public meetings. The whole process was thoroughly documented, with information about each alternative — along with hundreds of pages generated by the environmental review process and public commentary — easily found on the state’s Tappan Zee Bridge website.

On October 11, the Federal Highway Administration and Governor Andrew Cuomo’s office announced that the bridge project had been selected for expedited federal review. The project they promised to speed up, however, was vastly different from the one vetted over the course of nearly a decade. The new plan for the bridge promised to add space for car traffic but left the transit component to be completed at an unspecified future date. Transit advocates are skeptical that the commuter rail and BRT lines will ever see the light of day.

At the same time that transit was removed from the plan, the state expunged from the public record all information about the nine-year public process and the four design alternatives that included rail and bus lines. The Tappan Zee website no longer displays the documents it did two weeks ago, as blogger Cap’n Transit first noted. The endorsement of transit, the extensive environmental analysis, the history of public input — all of it gone, replaced by three short documents chronicling the brief history of the transit-free project.

So much for transparency. Kate Slevin, executive director of the Tri-State Transportation Campaign, said she couldn’t recall a single example of this kind of wholesale document scrubbing.

In addition to hiding the history of the Tappan Zee project, the state and federal agencies in charge won’t disclose how they reached the decision to build the bridge without transit.

When the Cuomo administration touted the selection of the Tappan Zee for expedited federal review, the announcement failed to mention that the project being expedited had also been utterly transformed. And it remains unclear who ultimately decided to abandon the transit component. Some media outlets reported that the federal government made the call; others implied it was the state. The New York Times reported that federal officials pushed for the transit elements to be postponed, while Transportation Nation noted that Cuomo hadn’t invited the MTA to his meetings on the Tappan Zee Bridge for months.

When Streetsblog asked the U.S. Department of Transportation which agency decided to remove transit from the bridge’s design and why, they directed us to the New York State DOT, which the feds said had “rescoped the project.” NYS DOT told us that the matter was being handled by the governor’s press office. Inquiries to Cuomo’s office were not answered.

A document jointly produced by the Federal Highway Administration, the New York State Department of Transportation and the New York State Thruway Authority provides the only public explanation for removing transit from the bridge design [PDF]. The joint explanation reads, in full:

In 2011, while advancing financial analysis, it was determined that funding for the corridor project (bridge replacement, highway improvements, and new transit service) was not possible at this time. The financing of the crossing alone, however, was considered affordable. Therefore, it was determined that the scope of the project should be limited, and efforts to replace the Hudson River crossing independent of the transit and highway elements should be advanced.

The aforementioned financial analysis, however, is not available on the Tappan Zee website. Why did the agencies consider it affordable and cost-effective to build a highway-only bridge — projected to cost $5.2 billion — while an estimated $1 billion more for bus rapid transit lines was too much? It’s impossible to tell.

Slevin called the statement “ten years of study and consensus erased by three sentences.”

One of the region’s most important transit projects was effectively canceled overnight, upending years of preparation for a high-quality transit option between Rockland and Westchester counties that could shape development, improve commutes, and decrease traffic congestion. New York residents deserve to know why the plans changed and who’s responsible, but so far the Cuomo and Obama administrations have denied them an explanation.