Major transportation projects built through a unique method state officials have championed lack clear guidelines, without which Texas taxpayers could end up paying more, according to a new report by the state’s auditor.

Released Wednesday, the audit of selected design-build contracts — including an upcoming segment of the Grand Parkway — found the Texas Department of Transportation “does not have a fully established framework to standardize its use of the design-build method.”

A dozen projects, among the state’s largest, have been or will be built through design-build, meaning a single team handles the engineering, planning and construction of the freeway work, with TxDOT oversight.

Combined, the projects represent $8 billion in road spending since September 2012 and continuing with current and upcoming projects. They range from improvements to roads in the energy sector to large portions of the Grand Parkway, Interstate 35 managed lanes and the replacement of the Harbor Bridge in Corpus Christi.

The auditor’s findings didn’t directly cast doubt on any of the projects or confirm officials’ assertions that the process helps Texas develop projects quicker and less expensively. Rather, the auditor found fault with TxDOT’s internal oversight of the procurement and bidding process.

“The lack of a fully established and documented framework for design-build projects resulted in several weaknesses and inconsistencies in (TxDOT)’s procurement and oversight of the four audited design-build projects,” according to the state auditor's report.

TxDOT spokeswoman Veronica Beyer said because some of the projects remain in a bidding process, officials were limited in what they could say.

"We appreciate the review from the (auditor) and we will be working to make improvements to our procurement process," Beyer said.

In responses included in the filing, TxDOT officials said most of those changes are expected by June, after they are approved by the Texas Transportation Commission.

In addition, changes to the upcoming extension of the Grand Parkway from U.S. 59 near Kingwood south to Interstate 10 drew critical attention from the state auditor. TxDOT, citing lack of growth in the northeastern area and high costs, changed the upcoming segments to have a single lane in both directions for most of the route, with some passing lanes.

Though the project changed from what officials listed when they asked companies for bids, TxDOT kept the bidding process going.

The audit found the agency lacked a written policy about what to do when a design-build project changes. It was the only one of seven recommendations the state auditor considered a high priority, though TxDOT in its response questioned the severity of the problem.

“Without a consistent, documented process establishing when design-build projects should be re-procured due to the nature and extent of changes to the project, there is an increased risk that a procurement may not be transparent and that (TxDOT) may not receive best value,” according to the audit.

“Specifically, the potentially significant changes to a project’s design and maintenance plan could garner additional interest from other qualified contractors that initially refrained from participating based on their consideration of the project’s original design scope.”

Officials expect to choose a builder for the upcoming Grand Parkway extension later this year, with construction anticipated in 2017. The lanes would not open until around 2021, under that schedule.