|Tennessee National Guard Parkway|
I-840 highlighted in red
|Maintained by TDOT|
|Length||77.28 mi  (124.37 km)|
|Existed||August 12, 2016–present|
|West end||I-40 near Dickson|
|East end||I-40 near Lebanon|
|Counties||Dickson, Hickman, Williamson, Rutherford, Wilson|
Interstate 840 (I-840), formerly State Route 840 (SR 840), also designated as Tennessee National Guard Parkway,  is a loop interstate highway around Nashville, Tennessee, built by the Tennessee Department of Transportation (TDOT). First proposed by former Governor Lamar Alexander as part of a system of Bicentennial Parkways, construction began in 1991 and was completed in 2012. The freeway is 77.28 miles (124.37 km) long,  and it serves the cities of Lebanon, Murfreesboro, Franklin, and Dickson.  
In 2015, approval was given by the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO) to redesignate SR 840 as Interstate 840 (I-840) as part of its integration into the Interstate Highway System. On August 12, 2016, TDOT announced that it would begin re-signing the route on August 14 and that work would be complete later in the year.
I-840 begins at an interchange in Cheatham County near Dickson. It initially runs southeast through a predominantly hilly terrain, and comes to an interchange with State Route 100 (SR 100) about 7.3 miles later. About ten miles later it crosses the Natchez Trace Parkway and turns east. I-840 has an interchange with U.S. Route 31 (US 31) about ten miles later, and about 3 miles later comes to an interchange with I-65 south of Franklin in an interchange that resembles a cloverstack interchange, containing two loop ramps and two underpass ramps that cross I-840 combined together. The route continues through a hilly terrain with several steep grades, and comes to an interchange with US 31 Alternate and 41 Alternate about 11 miles later. About 3 miles later I-840 crosses State Route 96 (SR 96), and about 9 miles later comes to an interchange with I-24 northeast of Murfreesboro. This interchange is almost a complete cloverleaf, containing three loop ramps and one flyover. The route turns northeast, passing through a predominantly rural and agricultural area, and about 19 miles later comes to an interchange with State Route 109 (SR 109). The route turns slightly northeast, and about 3.8 miles later reaches its eastern terminus with I-40 in Wilson County west of Lebanon. 
|Length||77.28 mi  (124.37 km)|
In 1975 the Tennessee Highway System Plan issued by TDOT for the next four years first identified the need for an outer beltway around Nashville within the next twenty years. 
The SR 840 project was initiated in 1986 with the passage of the Better Roads Program in the Tennessee General Assembly.  While initially referred to as Interstate 840 (I-840) in the state plan,  the highway was constructed entirely with state transportation funds and was officially referred to as a state route.  The first contract for construction was signed in 1991, and work progressed in stages. 
The first section of SR 840 between I-40 in Lebanon and Stewart's Ferry Pike opened in August 1995.  The extension to I-24 near Murfreesboro was completed in November 1996, and the section between I-24 and US 31 Alternate (US 31A) near Triune was completed in November 2000.  The portion between US 31A and I-65 near Franklin opened in October 2001. The section between I-40 near Dickson and SR 100 opened in December 2002.  Due to high costs and environmental concerns, the proposed northern half of SR 840 was indefinitely placed on hold in 2003.  The western terminus was constructed in anticipation of the northern loop.  As work moved into Williamson County, residents filed complaints and eventually lawsuits in an effort to have TDOT address both environmental and aesthetic issues, considerably slowing work in that county.  The full southern route of SR 840 was opened on November 2, 2012.  The project took 26 years to complete at a cost of $753.4 million. 
TDOT was first authorized to begin studies for a northern loop of I-840 north of Nashville and past Dickson, Clarksville, Springfield, and Gallatin by the state legislature in 1993.  Environmental studies began in 1994 and a draft environmental impact statement (DEIS) was released in 1995.  Many residents in the predominantly rural and agricultural areas where the route was to pass were initially opposed.  Plans were later abandoned and the General Assembly ordered TDOT to discontinue further studies and planning of that highway because of state budget problems. An entire circular loop would possibly be about 178 miles (286 km) long, ranging from 86 to 116 miles (138 to 187 km). Other important objections against additional extensions of the I-840 highway include the hilly nature of the terrain north of Nashville (the Highland Rim), which would require huge and costly amounts of excavation, soil relocation, and bridge construction. In October 2003, TDOT placed the northern loop plan on indefinite hold, citing a lack of documented transportation needs and lack of participation from local politicians. 
In 2015, TDOT submitted a request to AASHTO to redesignate SR 840 as I-840. Though the application had an error that required TDOT to refile it, AASHTO conditionally approved it and submitted it to the FHWA for their approval.   FHWA approved the change on July 22, 2015, and AASHTO finalized their approval on September 25, 2015.  TDOT announced that it would start replacing the signs to change over the designation the week of August 14, 2016, and that the project would be completed by the end of the year at a cost of $230,000. 
|Dickson||||0.0||0.0||1||I-40 – Nashville, Memphis||Signed as exits 1A (west) and 1B (east) westbound; I-40 exit 176; stub road westbound|
||No major junctions|
|Williamson||||7.3||11.7||7||SR 100 / SR 46 – Fairview, Centerville|
|||14.1||22.7||14||SR 46 (Pinewood Road) – Leiper's Fork|
|||22.9||36.9||23||SR 246 (Carters Creek Pike)|
|Thompson's Station||28.3||45.5||28||US 31 (Columbia Pike) / SR 6 – Columbia, Spring Hill, Franklin|
|30.3||48.8||30||US 431 / SR 106 (Lewisburg Pike) – Franklin, Lewisburg|
|||31.1||50.1||31||I-65 – Nashville, Huntsville, AL||Signed as exits 31A (south) and 31B (north); I-65 exit 59|
|Triune||41.9||67.4||42||US 31A / US 41A / SR 11 (Horton Highway) – Shelbyville, Lewisburg, Triune, Nolensville, Eagleville, Chapel Hill|
|Rutherford||||46.9||75.5||47||SR 102 (Almaville Road) – Smyrna|
|||50.8||81.8||50||Veterans Parkway – Blackman|
|Murfreesboro||53.1||85.5||53||I-24 – Nashville, Chattanooga||Signed as exits 53A (east) and 53B (west) westbound; I-24 exit 74|
|55.1||88.7||55||US 41 / US 70S / SR 1 (NW Broad Street / New Nashville Highway) – Murfreesboro, Smyrna||Signed as exits 55A (south/east) and 55B (north/west)|
|||57.8||93.0||57||Sulphur Springs Road|
|||61.4||98.8||61||SR 266 (West Jefferson Pike) – Smyrna|
|||65.2||104.9||65||SR 452 (Bill France Boulevard / Maddox Road / Mona Road) – Nashville Superspeedway|
|Wilson||||67.2||108.1||67||Couchville Pike||Exit to Cedars of Lebanon State Park|
|||70.6||113.6||70||Stewarts Ferry Pike – Gladeville|
|||72.0||115.9||72||SR 265 (Central Pike) to SR 109 north||Signed as 72A (east) and 72B (west) eastbound|
|||76.8||123.6||76||I-40 – Nashville, Knoxville, Lebanon||Signed as exits 76A (east) and left 76B (west); I-40 exit 235;|
|1.000 mi = 1.609 km; 1.000 km = 0.621 mi|
- Tennessee Department of Transportation (October 31, 2003). "TDOT Announces Decision on State Route 840 North" (PDF) (Press release). Tennessee Department of Transportation. Archived from the original (PDF) on November 27, 2007. Retrieved July 17, 2007.
- Tennessee Department of Transportation (2012). State Route 840: Enjoy the Ride (PDF) (Dedication program). Tennessee Department of Transportation. Archived from the original (PDF) on November 19, 2012. Retrieved June 12, 2015.
- Tennessee Department of Transportation (2014). Tennessee: 2014 Official Transportation Map (Map). c. 1:633,600. Nashville: Tennessee Department of Transportation. §§ C7–B8.
- Google (June 20, 2015). "State Route 840" (Map). Google Maps. Google. Retrieved June 20, 2015.
- Google (18 December 2017). "I-840" (Map). Google Maps. Google. Retrieved 18 December 2017.
- Proposed Route 840 North from Interstate 65 to Interstate 40 West of Nashville in Robertson, Cheatham, Dickson, and Montgomery Counties, Tennessee (Report). Federal Highway Administration. Retrieved December 18, 2017.
- Anderson, Skip (November 5, 2012). "State Route 840 Opening Ends Arduous, Laborious and Costly Project". The City Paper. Nashville, TN. Retrieved June 11, 2015.
- Tennessee Department of Transportation (n.d.). "SR 840 South: Brief History". Tennessee Department of Transportation. Archived from the original on July 14, 2007.
- Special Committee on U.S. Route Numbering (May 14, 2015). "Special Committee on U.S. Route Numbering Spring 2015 Report to the Standing Committee on Highways" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 6. Retrieved June 6, 2015.
- Wright, Bud (June 4, 2015). "Interstate Applications for I-840 TN" (PDF) (Letter). Letter to Greg Nadeau. Washington, DC: American Association of State Highway and Transportation Officials. Retrieved June 6, 2015.
- Special Committee on U.S. Route Numbering (September 25, 2015). "Special Committee on U.S. Route Numbering Report to the Standing Committee on Highways" (PDF) (Report). Washington, DC: American Association of State Highway and Transportation Officials. p. 1. Retrieved December 18, 2015.
- Tennessee Department of Transportation (August 12, 2016). "Tennessee Adds New 77 Miles of Highway to Interstate System: State Route 840 Now Designated as Interstate 840" (Press release). Tennessee Department of Transportation. Retrieved August 12, 2016.
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