On February 17, 2003 Public Works staff provided a bridge presentation to the Board of Mayor and Alderman (BMA). The first part of the presentation was an update on the status of the Netherland Inn bridge replacement project while the second part provided an overview of the condition of all of Kingsports bridges.

This Powerpoint presentation was adapted from the original BMA presentation and only includes the slides related to the update of the Netherland Inn bridge project. The comprehensive bridge report is available on-line at kingsportpublicworks.com under Reports and Presentations.

The two issues highlighted in this Netherland Inn bridge presentation include a discussion of the possible bridge construction impacts on Rotherwood Drive and TDOT utility restrictions on the new bridge.

The TDOT Bridge replacement project for the Netherland Inn Road bridge is in the design phase. TDOT originally developed plans that proposed to replace the bridge in the same footprint as the current bridge with the addition of approximately 20 25 of bridge width (noted in yellow shading). By choosing to maintain the existing alignment, significant private property (including one occupied home) would have had to be acquired for right-of-way purposes, traffic (12,000 vehicles/day) that rely on Netherland Inn Road to get in and out of downtown Kingsport would have had to be re-routed for an estimated 2-4 years (TDOT estimate), and the City would have had to design and construct a temporary sewer at an estimated cost of $500,000.

Due to these prospective adverse impacts resulting from the original TDOT proposal, the City requested consideration of an alternative bridge alignment. After working with a local bridge engineering firm City staff developed an alternative alignment concept (pictured above in blue) that would allow the bridge to be replaced but would also eliminate the need to acquire row that would displace a family, reduce the need for traffic detouring, and avoid temporary sewer construction costs.

The alternative alignment involves constructing the new bridge to the immediate south of the existing bridge. This option would allow traffic to continue unimpeded during the construction of the new bridge and the sewer could also remain in place and be transitioned over to the new bridge after it was constructed. This alignment would slightly alter the approaches at each end of the bridge (which would improve some of the traffic safety issues related to the side street entrances located at either end of the bridge) but it would also impact the parking area at Riverfront Park and small portions of the Rotherwood Mansion property (noted where blue shaded area overlaps orange property lines).

The alternative alignment concept was accepted by TDOT and approved by the environmental and historical review agencies in May 2002 thereby allowing the preliminary design work to proceed to final design. TDOT anticipates having final design complete in the Spring 2003 with construction likely to begin in early 2004.

In an effort to provide a better conceptual understanding of the proposed alternative bridge, Public Works staff developed the conceptual rendering shown above using before and after photos.

(Please remember that the rendering is not drawn to scale and it is not intended to necessarily match the final product exactly it is only intended to facilitate a better conceptual perspective of what the new bridge might look like.)

TDOT has not yet completed their final plans on the new bridge but they shared preliminary design plans at a field review meeting with City staff in November 2002. In their initial design for the alternative bridge, TDOT was showing the new bridge to be slightly sloped from east to west -- with the high end of the bridge on the park side and the low end landing on the Rotherwood side. Based on this design Netherland Inn road would also have to be adjusted to provide smooth transition at each end of the new bridge.

How much the roads have to be adjusted (both up and down, and side to side) is driven by engineering standards for roadway design that are based upon the design speed of the road. For each speed there are specific vertical and horizontal limits for acceptable slopes. In general, the slower the design speed the more sloped the transition between the bridge and the adjoining roads is allowed to be and likewise the faster the speed the lower the tolerance for changes in elevation. These standards are all based upon traffic safety requirements.

In their initial design, TDOT staff reported that they had to lower the western-most part of the bridge in order to match the existing driveway height for the Rotherwood Mansion which is 4-6 feet below the height of the existing Netherland Inn Road. However, lowering Netherland Inn to the height of the Rotherwood Mansion driveway subsequently creates problems at the Netherland Inn / Rotherwood Drive intersection.

The profile view of the bridge shown at the top (not drawn to scale) provides a view of the cross section of the bridge and roadway slopes. The pink line represents the existing bridge and current roadway slopes. The yellow line shows the proposed raise in elevation on the east end (park side) of the bridge and the corresponding lowering of Netherland Inn Road west of the bridge in order to comply with roadway design standards for vertical alignment.

By raising the eastern portion of the bridge, shifting the new bridge to the south, and lowering the western portions of Netherland Inn Road, the intersection of Netherland Inn Road and Rotherwood Drive will no longer be in alignment in effect, Rotherwood Drive would sit 2-4 higher than the pavement for the new Netherland Inn Road.

Since the existing Rotherwood Drive slope (1) is already steeper than current road design standards, it is not feasible to simply make the Rotherwood Drive slope steeper (2) in order to reach the lowered Netherland Inn road. Rather, TDOT is proposing to cut back and re-grade the entire entrance and first 1,000 feet of Rotherwood Drive to allow a more gradual transition and flatter slope into the intersection at Netherland Inn road (3).

Looking down from the aerial view at the top left, the problematic intersection is noted in the light blue box where the new Netherland Inn road and existing Rotherwood Drive intersect. The inset picture in the lower right provides a current view of the entrance-way of Rotherwood Drive (looking north) with the proposed re-location of the in-bound and out-bound lanes of Rotherwood Drive. TDOT has proposed to lower these lanes to the height of pink line in order to allow a gradual and safe approach to the intersection at Netherland Inn Road. (It is important to note that the final elevation of the re-located lanes has not been determined by TDOT yet so this image is for conceptual purposes only and does not necessarily represent the final height of the road.)

TDOT engineers report that in their design the two lanes of Rotherwood Drive had to be moved as far as possible on the down-hill side in order to minimize the amount of excavation that will be required to lower Rotherwood Drive to an acceptable height to safely intersect with Netherland Inn Road. This would eliminate the grassy median between the two lanes but the TDOT engineers noted that the project would include an appropriate amount of landscaping in the abandoned portions of the existing right of way as compensation for whatever is taken by the re-located lanes.

TDOT has advised the City that the re-grading and re-location of Rotherwood Drive would add approximately $800,000 to the overall costs of the bridge project of which 20% or $160,000 would be the Citys share. TDOT engineers noted that with only one entrance into and out of the Rotherwood neighborhood the re-location of the lanes would be a construction challenge since ingress and egress would have to be maintained at all times.

Given the extent of the neighborhood impacts and the additional costs to the project resulting from the re-grading of Rotherwood Drive, the City of Kingsport has retained the services of a professional bridge engineering firm to try to re-work the bridge and roadway elevations so that Rotherwood Drive would not be impacted and would not have to be changed. This re-engineering work is underway and new roadway profiles are being developed for presentation to TDOT in Spring 2003. TDOT has been advised of the Citys efforts to re-work the plans and they have invited the Citys input.

All the wastewater generated by City residents west of the North fork of the Holston River (e.g., Rotherwood Estates, Rotherwood Manor, Bays Cove, Allandale, etc.) flows back towards the river and is piped over the river (noted in orange) through a ductile iron pipe (see inset picture) that is built into the truss structure of the existing bridge in order to ultimately convey wastewater to the wastewater treatment plant on Industry Drive. There is also an old abandoned waterline that would be re-activated in conjunction with the bridge construction project in order to improve water service redundancy in the west end of Kingsport.

One of the principle reasons for requesting the construction of a new bridge immediately adjacent to the existing bridge was to avoid the need to build a temporary sewer line (noted in yellow) to carry wastewater across the river when the existing bridge was torn down. Relocating this large sewer line into the river bed would be very expensive (estimated at $500,000) and would put wastewater conveyance pipes in environmentally sensitive areas. In addition, this option would require the construction of a large sewer lift station (similar in size to the station at the corner of Netherland Inn and Ridgefields Road) in order to push the wastewater up the hill from the river bed back up to the existing grade of the sewer lines on the east side of the bridge.

These wastewater issues were presented to TDOT as part of the Citys appeal to build a new bridge adjacent to the old bridge in order to allow the existing lines to be kept in service until the new bridge and new utility lines were constructed on the new bridge. The TDOT design engineers agreed with the Citys concept plan. However, as the bridge replacement project has moved forward the TDOT bridge design engineers have subsequently advised the City that no utility lines would be allowed on the new bridge. However, in response to the Citys protests, TDOT reluctantly agreed to allow the utility lines to be located on the new bridge but they could not be placed on the same grade that they exist on the current bridge rather TDOT would only allow the utilities to be relocated immediately beneath the new bridge decking which is 20-30 higher than the current lines.

Current bridge design standards use concrete columns with hammer-head tops (see schematic view of the new Rotherwood bridge above) to support the bridge decking instead of the steel trusses. As a result, TDOTs engineers have advised the City that the new bridge will not provide the same structure to hang the utility pipes on at their current grade (noted in orange) and as a result the installation of the utilities will be restricted to immediately below the bridge decking (noted in yellow) at a much higher grade.

This information was provided to the City for the first time in November 2002 and as the City staff evaluated this restriction it became evident that a large sewer lift station (comparable in size to the lift station at the intersection of Netherland Inn Road and Ridgefields Road) would need to be constructed to push the wastewater up to the height of the new bridge decking. As an alternative to a new lift station staff re-considered the option to keep the old bridge in place after the new bridge was constructed for continued use for utilities and pedestrians/bicyclists.

In order to evaluate the feasibility of the two bridge option, Public Works staff assessed the aesthetic impacts of keeping two bridges in place, the functional viability of the existing bridge, and the project cost impacts associated with building the new bridge and keeping the old one in place for use by pedestrians and bicyclists.

From an aesthetic point of view, a photo rendering was prepared (see above Alternative C with existing bridge) to provide some visual perspective of what the two bridges might look like side by side. Other cities have successfully converted old bridges into pedestrian walkways and based on the preliminary (not to scale) view provided above, it would seem that the idea might be workable with the appropriate level of investment in some complementary lighting, landscaping and surface restoration to the existing bridge in order to reasonably match the look of the new bridge which TDOT has agreed to build with attention to historical quality such as historic lighting fixtures, attractive bridge rails and other historic features.

The utilities are in place and easy to work on under the existing bridge so from a functional / maintenance perspective keeping the existing bridge in place for utility lines is a highly attractive option.

Any other option (either placing sewers in river bed or hanging sewers immediately beneath the decking on the new bridge) requires building a sewer lift station and even if building a sewer lift station was deemed acceptable from a cost perspective ($250,000), the prospect of maintaining and/or repairing breaks or leaks in a sewer line that is suspended immediately under the bridge decking would require renting highly specialized equipment that would allow maintenance employees to be extended in a bucket 80 feet over the water under the bridge. Mobilizing for this type of repair would be time consuming and expensive whereas the pipes in place on the existing bridge are very easy to access and to repair quickly without specialized equipment.

Likewise, if the sewer line was embedded in the river bed rather than under the decking, repairs would involve increased employee safety risks and further specialized equipment to perform the work in/under water.

Therefore, from a functional perspective, keeping the existing bridge is the optimal choice.

In replacing the existing bridge the City had specifically requested that TDOT include a 6 bike lane and a wide (5) sidewalk on the southern side of the new bridge in order to improve safe pedestrian and bike linkage to the Greenbelt that begins on the east side of the bridge. The City had also planned to extend sidewalk up to Rotherwood Estates and eventually all the way up to Stone Drive to further expand safe access to the Greenbelt with this project.

Keeping the old bridge for use as a designated pedestrian / bike lane essentially replaces the need to build the sidewalk or the bike lane on the new bridge. As a result, TDOT reports that the new bridge construction costs would reduced by $200,000 (City pays 20% or $40,000) for the elimination of sidewalks and $100,000 (City share $20,000) by not proceeding to demolish the existing structure.

From a functional perspective the use of the existing bridge would require either a surface crossing to get over to the Greenbelt side of the road or a wrap-under path to provide a direct connection to the Greenbelt extended beneath the existing bridge.

As a result of the repairs performed on the bridge in the summer/fall of 2002, the bridge was restored to a safe condition and re-opened in November 2002. At a cost of $565,000 the bridge repairs included removal and replacement of weakened steel beams and overall structural rehabilitation. The Citys bridge engineers have indicated that the repairs were significant enough to ensure that the bridge can withstand up to 10 years of full traffic or nearly 100 years if bridge traffic was reduced to a pedestrian / bikes only.

With this information in mind, the prospect of keeping the old bridge in place seems very reasonable for another 100 years of service life.

From a cost perspective, there is a fair amount of financial incentive to keep the old bridge in place for use by pedestrians and for utilities. TDOT has estimated demolition costs associated with the bridge project to be approximately $100,000 of which the City contributes $20,000 or 20%. And if sewer service remains on the old bridge, the City will save an estimated $250,000 from avoiding having to build any new sewer lines and lift stations. And lastly, TDOTs engineers have reported a probable savings of $200,000 by avoiding have to build sidewalks on the new bridge if the old bridge is converted to a pedestrian/bike path. All combined, keeping the existing bridge in place is estimated to save $310,000 in capital costs with a likely $5,000 a year in routine bridge maintenance costs for the pedestrian bridge.

In summary, Public Works staff will continue to work with the Citys bridge engineering firm over the next couple of months to re-design the new Netherland Inn bridge so that the roadway alignment problems can be resolved without impacting the intersection of Rotherwood Drive and Netherland Inn Road; and based on the direction of the BMA, staff will formally convey the Citys request to TDOT to keep the old bridge in place for use by pedestrians and bicyclists and for City utilities.