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Difference between revisions of "Tennessee/Interpreting TDOT Maps"

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This page serves as a supplemental tutorial to help explain some of the rationale behind select Tennessee mapping standards in greater detail than is appropriate for the primary [[Tennessee|Tennessee wiki]] page.  
This page serves as a supplemental tutorial to help explain some of the rationale behind select Tennessee mapping standards in greater detail than is appropriate for the primary [[Tennessee|Tennessee wiki]] page.  

Latest revision as of 04:43, 7 March 2017

This page serves as a supplemental tutorial to help explain some of the rationale behind select Tennessee mapping standards in greater detail than is appropriate for the primary Tennessee wiki page.

With very few exceptions, every road that is classified as Primary Street or as one of the Highway types will be found on the TDOT Functional Classification Maps. These maps are the key to understanding not only what the proper Waze road type should be, but are also used to determine state highway numbers and naming format.

Who maintains Tennessee roads?

It may be helpful to think of Tennessee roads as belonging to four overlapping networks:

Federal: A network of interstates, US highways, and state and local roads that are part of the National Highway System maintained by the state using federal funding to some degree. State roads that are part of this network can be identified on the TDOT Functional Classification Maps by the small letters "NHS" above the highway shield. These are usually classified in Waze as either  Freeway  or  Major Highway , but occasionally as  Minor Highway .

Example: in Roane/Anderson Counties, TN-95 is part of the NHS because it serves as important access to the facilities at Oak Ridge.

State and locally maintained roads found on TDOT maps: TDOT also maintains a network of state highways in each county using state funds. Overall, this is a fairly small percentage of the total road mileage in each county, and will be mapped as  Freeway ,  Major Highway ,  Minor Highway , or  Primary Street .

Local roads not shown on TDOT maps: Individual counties (and many cities) maintain a network of local streets and roads composing the majority of road miles within the state. These will be  Street  type unless they are private or unpaved roads. Individual jurisdictions may use unique road naming/numbering schemes and some maintain their own GIS websites, so road names and sources of reliable information will vary between counties. For example, Monroe and Meigs counties assign numbers to many county roads, though they may also have local names as well. Incorporated municipalities typically have their own highway departments charged with maintenance and upkeep of these roads.

National Park Service and US Forest Service roads: The NPS maintains a network of roads within national parks and various other park units, as well as two scenic roads: the Natchez Trace Parkway and the Foothills Parkway. These roads use a functional classification system that is separate from the rest of the state, and most of them do not appear on TDOT maps. See for mapping guidelines. These roads receive special attention by state and area managers and, in general, should not be changed before consulting with these editors.

Example: When Great Smoky Mountains National Park was established, there were already several state roads across land that was transferred to the NPS. All state highway designations were abolished within the park boundary, and no state funds are currently used to maintain roads within the park. As part of the agreement that saw TN roads turned over to the federal government, no tolls may be collected on these highways - this is why the Smokies is one of the few national parks with no entrance fee.

Within the Cherokee National Forest is a network of forest roads, many of which are only open seasonally. Like roads administered by the National Park Service, forest roads have their own naming and mapping conventions:

How to determine road number using a TDOT FC map

In short, it is the shield shape that determines what number format to use.

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1) This has a triangle shield, so it is a "secondary state highway" that will be given the number SR-181.

2) This has a rectangle shield, and so is TN-181. It is a "primary state highway" but note that it is also number 181 just like the first example. The primary/secondary designation is based on road use (functional classification) and there are numerous examples of state highways that switch between primary and secondary at different points along the route.

3) The number 01505 is NOT mapped in Waze. It would be given the primary name of Miston Tank Rd. These 5-digit numbers, beginning with zero, are never found on highway signs; they are only used internally by TDOT to refer to county maintained roads that appear on state maps.

4) This is US-51, and TN-3. The TN-3 number would be listed as an alternate name, but is not signed on the actual highway. All US highways within the state also have one or more associated state highway numbers.

How to determine road type using a TDOT FC map

This section serves as a supplement to the Functional Classification section of the TN wiki page. Be sure to review that section for current classification standards. Each map has a legend, as shown in the image below, and roads are color coded based on their intended use.

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1) This is a major collector, which would typically be a primary street. But, since it is also a state highway (247) as indicated by the triangle shield, it would be upgraded to  Minor Highway , the minimum Waze classification for TN numbered state highways.

2) This is also a major collector; it is identified by the name Kendron Rd and the number 01907. These five digit numbers, which usually begin with a zero, are NOT mapped in Waze, and are NOT state route numbers! They are simply internal reference numbers that TDOT uses to track locally maintained roads that are shown on their maps. Therefore, this would be a  Primary Street .

3) This is a minor collector called Greens Mill Rd. It does not have a state highway number, and is maintained by the county. Similar to #2, the number 00972 is not mapped in Waze, and this would be a  Primary Street .

4) This is a principal arterial road, which makes it a  Major Highway . It is both US-31 and TN-6, as indicated by the presence of both shields, and is also called Main St. It is up to the editor to determine which of these three names belongs in the primary name field in Waze, and which two should be alternate names.

5) This is a freeway, TN-396, and should be a  Freeway  in Waze. It is also called Saturn Pkwy.

Oddities of Tennessee highways

Hidden state routes on US highways: In Tennessee, most US highways are also assigned a "hidden" state route number. These routes are often unsigned when they share a concurrency with a US highway. There are several ways to find them, although it can sometimes be tricky to determine the exact route that a hidden highway follows. First, the TDOT maps often display these hidden route numbers beside the US highway shields. Second, in street view, examine mile markers closely... there is often a small number below the mileage - this is the hidden state highway number. These state highway designations should be listed in the alternate name for the US highway segment.

Example: TN-1 follows US-70 and several other US highways across most of the state from Memphis to Bristol, but is only signed in certain areas.

Note that TDOT is notorious for referring to US highways only by their state route number, even if this number is completely hidden from signage. This can be especially confusing to motorists trying to determine what road traffic incidents or construction reports are referencing. For example, electronic signs on I-40 in Knoxville may indicate “accident on SR-115 SB” whereas this road is completely unsigned and is actually US-129. In addition, incident reports on the Smartway map product almost always list the state route number and fail to mention the associated US-highway. It is for this reason that these should be mapped as alternate names in Waze.

Routes that switch between primary and secondary: There is no set rule as to whether a given state highway will be primary (rectangle shield) or secondary (triangle shield), though it is usually the case that roads classified as “Arterials” by TDOT are primary (rectangle shield) while “Connectors” are usually secondary (triangle shield). Actually, it is not unheard of for a single numbered route to be primary for part of its length and secondary on other sections, or even be a hidden concurrency at other times! However, it is generally the case that the lower numbers (1-100) tend to be associated with arterial roads, are longer and more likely to traverse multiple counties, and are more often primary routes; numbers 100-477 are often assigned to shorter connector roads, typically contained within one county, and tend to have the secondary shield.

The only state road numbered higher than 477 is TN-840, an interstate-grade freeway that acts as a bypass loop for I-40 around Nashville. The reasoning behind this number is that, once the road is actually designated an interstate, it will be I-840. While this interstate route number is out of sequence given the road’s central location within the state, I-240, 440, and 640 already existed prior to this road’s conception.

One may notice patterns in the higher numbered roads (above 200) such as where an individual county contains a network of secondary TN highways with similar numbers. For example, Blount County includes TN-333, TN-334, TN-335, and TN-336.

Example: TN-33 crosses N-S from the Virginia state line to Georgia. It is, in various locations, either a primary or secondary state highway, and in a few places is a "hidden" state route that follows US-411.

Cardinal directions that don't match even or odd numbered roads: State routes follow no convention as far as directionality. When traveling along an interstate or a US highway, one can expect that even numbered roads run east-west while odd numbered roads run north-south. In contrast, It is possible to find odd numbered state highways that run both N-S and E-W, and the same is true for even numbered roads. There are also cases (for example, TN-385 around Memphis) where cardinal direction signage changes as one proceeds along the highway.

Alternate and split US highways: One oddity of US highways that is seen almost exclusively in our region is the use of "parallel" routes. These can be identified by the inclusion of a single letter representing a cardinal direction that is *inside* the highway shield. An easy way to distinguish these from divided/split highways is that the cardinal direction runs perpendicular to the direction of travel... for example, US-11, being an odd numbered highway, runs north-south, but its two split highways are US-11E and US-11W. In contrast to a divided highway, in which the opposing travel lanes are separated by a median, travel on each parallel route is possible in both directions, and the routes may be separated by many miles... often traversing entirely different counties. These are NOT to be treated like bannered routes, and are not considered alternate or bypass routes; rather they are the same highway that follows two (or even three!) separate paths across a broad area.

There are also some roads which are combinations of both parallel and bannered highways. For example, US-70S BUS in McMinnville is the business spur of US-70S, which is itself a split route running east-west across the state parallel to US-70 (which passes through Smithville) and US-70N (through Cookeville). Neither US-70N nor US-70S are considered to be bannered routes.

Nostalgic names: It is very common to see historic or honorary names on highway segments, especially US highways. Some of these are remnants of the pre-1926 auto trail system, others might be associated with the America's Byways program, or the name might be in honor of a local politician. These include things like “Great River Road” "Broadway of America" or "Dixie Highway" or the road may even have large green signs honoring historical figures such as "Alvin C. York Highway." A bit of research may be needed to determine whether these are actual names, or simply honorary designations. Use caution and do some homework before deleting these, but don't assume that they belong just because they are present.

Example: In Loudon County west of Knoxville, the convergence of US-11 and US-70 is locally known as "Dixie Lee Junction" because this is the point where the historic Dixie Highway and Lee Highway met. These names were eventually replaced with US highway numbers, but not forgotten by locals.