Editor's note: This story has been updated throughout.

The Texas Department of Transportation could soon answer some of the biggest questions looming over a controversial Dallas plan to build a toll road alongside a massive urban park inside a flood plain.

Chief among those questions is whether a divisive road project born in the 1990s is a solid bet for solving a bevy of intertwined urban challenges in the 21st century or just an outdated approach likely to exacerbate existing problems.

Dallas Mayor Mike Rawlings wants the agency to analyze plans for the Trinity Parkway as part of an existing study of downtown highways called CityMAP. That report looks beyond highway congestion forecasts to also estimate how different construction scenarios — including the removal of one particular downtown highway — would affect economic development, neighborhood connectivity and the quality of life for nearby residents. 

The Texas Tribune thanks its sponsors. Become one.

But first, Rawlings said, he wants the state transportation agency to determine if a scaled-down version of the project would reduce traffic on nearby highways the way a high-speed, larger version would. 

"If it doesn't accomplish that, I don't understand why anybody would spend any money," Rawlings said Tuesday.

Federal highway officials last year approved a version of Trinity Parkway that would include at least three lanes in each direction and several large interchange ramps that connect to downtown-area streets and highways. The approval was predicated on a forecasted slight reduction to traffic on nearby Interstates 30 and 35E.

That version of the road is controversial for several reasons. It is much larger than the iteration voters were shown in 2007; people fear it would be inhospitable to the nearby park; and the new road would dramatically increase traffic on highways outside of downtown. 

"The omission of the Trinity Parkway leaves unanswered questions and a disconnect from Dallas CityMAP that should be rectified," Rawlings said in his request to include the road in the study. 

In his letter, he also said that the city shouldn’t build a large-scale, high-speed version of the road that federal officials approved last year. Many in the city oppose that version of the road. 

The Texas Tribune thanks its sponsors. Become one.

But Rawlings added in his letter to TxDOT that a different version of the road would need to relieve traffic on nearby Interstate 35E. Expected congestion reduction on that existing downtown highway and Interstate 30 helped the city garner federal approval of Trinity Parkway in the first place.

Those slight traffic reductions would be accompanied by dramatic increases in congestion on other downtown-area highways.

Project supporters for months have hailed unfinished plans for a narrower, slower version of the road as a compromise that could unite the city around the project. But those claims often omitted the fact that federal officials expect the large-scale version to be built eventually, even if a smaller version is built as a first phase of construction.

Their claims have also lacked detailed traffic estimates that would show whether a smaller version reduces traffic on Interstates 30 and 35E as they converge downtown.

Former Dallas City Council member Angela Hunt has been a longtime critic of how city officials and regional planners have developed, overseen and publicly portrayed the road. She, too, wants to see whether a scaled-down version would provide long-promised traffic benefits.

But Hunt said the data and methods used should be made public so residents know they aren't being skewed to justify a smaller version of the road.

"There is so much political pressure surrounding this issue from those that support the toll road," Hunt said. 

TxDOT’s CityMAP includes some traffic impact data that shows how different construction scenarios on other downtown highways would affect traffic on other corridors. Draft copies of CityMAP were publicly released this year. But agency officials and consultants have been revising portions based on input from the public and officials. It’s unclear how long the final version would be delayed if the agency adds Trinity Parkway to the report. TxDOT employees were slated to meet about adding a Trinity Parkway analysis to CityMAP on Tuesday.

The Texas Tribune thanks its sponsors. Become one.

Rawlings said in his letter that Trinity Parkway could be a “realistic way” to improve the entire transportation network in the city’s urban core.

“But we must develop it in a manner that the citizens of Dallas will be comfortable with,” he said.

In his request for the analysis, Rawlings said the city shouldn’t build a large-scale, high-speed version of the road that federal officials approved last year. 

He and Craig Holcomb, executive director of nonprofit Trinity Commons Foundation, said the city should work within the approval it's already received since that process took more than a decade and cost tens of millions of dollars. 

"To throw all of that away would be incredibly wasteful," Holcomb said.

But building small now under existing approvals leaves open the door to future city councils expanding the road into the larger version that many residents oppose. 

Hunt said the city should then scrap the approved version of the road, design something new and begin federal approvals again. 

"We are lying either to the federal government or to the people of Dallas because you can't have both," she said.

Never miss a moment in Texas politics with our daily newsletter.