The Arkansas State Highway and Transportation Department (AHTD) also plans call for doubling the width of Highway 63 south of the Missouri border, from two lanes to four, to about where it meets Highway 342.
Linda Gunn, the department's staff engineer of urban design, said AHTD is planning for the future, anticipating additional truck and car traffic once the three bridges are replaced.
Gunn emphasized the department is in the very early planning stages of the project, which would not likely see construction until at least 2013.
"Our concern is the bridges, and we have some bridge money," Gunn said.
The bridges over Spring River at the junction of Highway 9, over the railroad tracks just south of there and over Trace Creek north of Long Run Road are proposed to be widened if the project is approved.
Some improvements have been made to the road in recent years, including the addition of passing lanes, although the intersection in front of the entrance to Mammoth Spring State Park has not been updated since about the 1950s.
Those at the meeting also included Mammoth Spring Mayor Jean Pace, business owners and several representatives of the state park.
Residents asked whether a signal light would be added at the Highway 9 junction, while others voiced concerns about having semi trucks stop at the bottom of the hill.
Gunn said signal lights are expensive and not part of the current plan, although engineers would study the need for the light, which could then become a future project.
A request for a traffic study will be ordered, Gunn said.
This project, Gunn said, calls for buying some right of way. In some areas, the right of way extends farther than initially seems necessary. The extra space is required in case of rock failure, she said.
"We always try to buy a little extra property," Gunn said. "We try to be very respectful of people and property, and at the same time, make it safe."
Residents also questioned whether the curve at the end of the project near the southern end of the project could be improved.
Gunn said the curve would be straightened only slightly where it then goes east over Trace Creek.
"It will actually be very scenic when it's done," Gunn said.
The state will accept public comments until June 24. Comments can be mailed to AHTD, Environmental Division, P.O. Box 2261, Little Rock, AR 72203-2261.