Traffic firm: Jackson's Main Street needs help, roundabouts may not be answer

It’s a familiar sight to Jackson commuters in peak hours: traffic backed up for hundreds of feet at East Main Street and Shawnee Boulevard, then again at East Main and Oak Hill Road.

A comprehensive traffic study of the entire Jackson city area is being conducted in 2017, but a specific study of these two intersections was conducted by Lochmueller Group of St. Louis, partially funded by a Missouri Department of Transportation grant.

Cheryl Sharp, Lochmueller representative, spoke to the Jackson Board of Aldermen on Monday, giving results of the study and recommendations for improvements.

Sharp said each intersection was assessed using accurate traffic counts during peak morning and evening hours, while school was in session, Tuesday through Thursday, in good weather. The intersections were given a letter grade for morning and evening peak times, based on estimated wait times for each car at the intersection.

A grade of “A” means the intersection is performing optimally, with zero- to 10-second delay per vehicle. “B” is close to optimal with a 10- to 15-second delay. “C” is acceptable, “D” begins falling below acceptable levels, “E” is near capacity and “F” is at full capacity.

Grades of A through C are considered acceptable for a community Jackson’s size, Sharp said.

Neither East Main and Shawnee nor East Main and Oak Hill are performing acceptably at peak hours, Sharp said.

Both intersections have a stop sign at all four points of entry, and East Main Street has left-hand turn bays both eastbound and westbound.

Sharp said Lochmueller looked at different models to address performance, including changing the intersections to roundabouts, adding traffic signals or re-striping the intersections to add turn lanes.

“Roundabouts are great because, after the initial investment, the city has no operations or maintenance costs down the road,” Sharp said.

Unfortunately, the intersection at East Main and Oak Hill is not ideal for a roundabout, Sharp said.

Roundabouts work best where each entering street is perpendicular, she said, with maximum distance between each leg improving sight lines.

Oak Hill Road is not perpendicular to East Main Street.

“Because of the intersection skew, it would end up more like a peanut-about, almost like a dual roundabout,” Sharp said, adding the roundabout would have a larger than normal footprint to accommodate the extra needed space, and the potential to affect adjacent properties also would be greater.

Sharp cited a residential driveway that would be directly inside the roundabout, for example, and a retention basin on the northeast corner of the intersection that would be affected.

“There are grade issues, too, on the northeast and southeast corners,” Sharp said.

Lochmueller recommended adding a traffic signal to the intersection, Sharp said, especially because left-turn bays already exist on eastbound and westbound Main Street, and traffic from Oak Hill Road is significantly less than from Main Street.

A traffic signal would be completely responsive to traffic demand, Sharp said.

As an example, “you’re not going to come up to it at 1 p.m. and sit there for 45 seconds waiting,” she said.

At East Main Street and Shawnee Boulevard, the intersection is closer to being perpendicular, but other factors led Lochmueller to recommend against a roundabout at this intersection as well.

“The difficulty with a roundabout at this intersection is, the needed radius is typically 110 feet to 140 feet in diameter, because of trucks,” Sharp said.

Power lines on the west side of the road and an existing large box culvert complicate that size roundabout, she said.

“I don’t think we could get 140 feet without impacting the stream going through there,” she said.

Sharp said the culvert and power lines also complicate the addition of a traffic signal, but not as significantly.

Sharp said one way to address the traffic issue at Shawnee and East Main is to re-stripe the lanes to add a right-turn lane on Main.

“The pavement there is 33 feet right now, and could be striped into three, 11-foot lanes,” Sharp said, but that measure would not adequately address long-term traffic-flow concerns.

Sharp said Lochmueller recommended a traffic signal at this intersection as well.

mniederkorn@semissourian.com

(573) 388-3630

Pertinent address:

East Main Street and Oak Hill Road, Jackson, Mo.

East Main Street and Shawnee Boulevard, Jackson, Mo.