GRAND RAPIDS, Mich. (WOOD) — A national transportation research group says Michigan’s $4.2 billion plan to fund road and highway projects across the state isn’t enough.

In 2015, state lawmakers reached a deal to raise fuel taxes and vehicle registration fees to fund infrastructure investment. Those increases started going in to effect this year.

Tuesday, research group TRIP released its findings on the plan. The group, which has conducted studies on roads for nearly 50 years, told 24 Hour News 8 that Michigan faces one of the largest pavement challenges in the nation.>>PDF: Report from TRIP

The $4.2 billion will be dispersed by lawmakers over the next six years. $2.3 billion of it is not guaranteed and its distribution is at the discretion of state lawmakers, according to TRIP.

The money makes it possible to complete many West Michigan projects, but leaves a number of others unfunded. Rocky Moretti, director of Policy and Research for TRIP, said those extra projects would cost an additional $200 million.

“The Michigan Department of Transportation (MDOT) said that right now, the highways and roads that they maintain — which are also the most critical roadways in the state — currently, 20 percent have pavements in poor condition,” Moretti said, speaking at the Grand Rapids Area Chamber of Commerce on Tuesday. “They (MDOT) anticipate by 2020, that number will increase to 46 percent.”

Moretti said that’s the case even factoring in the additional funding approved in 2015.

He added that the number of structurally-deficient bridges in Michigan is expected to increase by 50 percent by 2023 if more funding isn’t added.

“The challenge in Michigan is that the deterioration of major roads, highways, and bridges got to such a point in the last 15 years that then the repairs become that much more costly,” Moretti said.