The change will be fully in place by Friday morning, Nov. 6, and will remain in effect through the spring of 2010. Drivers who need to reach nearby CoxHealth facilities, including Cox South Hospital, and the many other businesses along National will be able to do so, but it probably will take more time to get there.

It would be best if drivers who use National to commute through the area, especially southbound during afternoon rush hour, can find other routes to avoid the construction and reduce the congestion along the corridor.

Construction of an underpass and service road under National -- half at a time -- is about to begin. That's why it's necessary to narrow National and shift traffic to the east side of the street.

Here's what will happen:

* National will have only one southbound lane open between Bradford Parkway (south of Primrose Street) and the bridge over the freeway starting some time Thursday evening. Even though only a 500-foot section of National will be narrowed, major driving delays are likely, especially for southbound National traffic.

Southbound National will have two through lanes open across the bridge and a separate left-turn lane to the eastbound freeway.

* Northbound National will have two lanes open on the bridge over the freeway -- one through lane and one left-turn lane onto the westbound freeway.

North of the bridge, National will have two lanes open through the work zone. The goal is to minimize traffic backups on the westbound freeway off-ramp to National.

* In late March or April, traffic will be shifted to the west side of National, with two lanes open for northbound traffic and one lane open for southbound traffic. This will allow the east side of the underpass to be built.

The project involves reconfiguring the National bridge into a Diverging Diamond Interchange, adding auxiliary lanes on the freeway between National and Campbell avenues and building an underpass and service road that will connect CoxHealth facillities on both sides of National north of the bridge.

The project will cost $9.7 million, including $7.5 million for construction and $2.2 million for engineering and right-of-way acquisition. Springfield, CoxHealth and MoDOT will share the cost.

The prime contractor is Emery Sapp and Sons of Columbia. The project is scheduled for completion next August.

The project will:

* Widen the National bridge (10 feet on each side) over the freeway to provide three lanes in each direction across the bridge. The bridge is in good condition and does not have to be replaced or undergo significant repairs. The bridge deck will be sealed.

* Widen ramps. Dual right-turn lanes will be provided from the westbound freeway ramp to northbound National.

* Build a pedestrian walkway down the middle of the National bridge.

* Add a lane in each direction on National south of the bridge to Kingsley Street and north of the bridge to Bradford.

* Build an additional lane in each direction on the freeway connecting the ramps at National and Campbell.

* Build a service road and underpass under National north of the freeway to improve connections between CoxHealth facilities on both sides of National and provide safer entry to Cox South Hospital, including its emergency department. This also will improve traffic flow and safety for drivers on National going past the CoxHealth facilities.

* Convert the interchange into a Diverging Diamond Interchange design where the opposing lanes of National will criss-cross at traffic signals at the ends of the bridge over the freeway. Crossing the bridge, oncoming traffic will be on the right. Opposing lanes will be divided by concrete barriers, with a pedestrian walkway in between the walls.

This configuration will provide left-turning vehicles on National a "free left" onto the freeway ramps. At the same time, traffic continuing north or south on National will be able to travel more steadily through the interchange, reducing backups. Signs, pavement markings and concrete islands will clearly guide drivers and help prevent making a wrong turn into the opposing lanes.