KEY ASPECTS OF NAVIGATION - TMC Information 1. TMC Information – Overview What are TMCs...

KEY ASPECTS OF NAVIGATION - TMC Information

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TMC Information – Overview

What are TMCs (Definition)? Where does the information come from? Conclusion

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TMC Information – Definition

Definition:

– Application of the FM broadcasting system used to report real-time traffic information

– Traffic information comes from drivers, emergency services, etc. and is transmitted by traffic information centers to local FM radio stations

– TMC equipped car radio or navigation systems pick up the signal and warn the driver of the traffic obstruction

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TMC Information – TMC Locations and Paths

TMC Locations can occur at intersections, bridges, tunnels, county or state boundaries, points of interest, or other recognizable real world locations.

What real world location is referenced by the TMC Master Table is inferred from the following pieces of information:

– Path name: this describes the road segments that make up the location and associated path.

– Cross-street information: this may contain a cross street, exit number, or other descriptive information about where along the actual path a location is composed.

– Lat-Long information: Should show the approximate coordinates of the location.

The location for any path must be either a single node or a series of connected segments. Forward and Reverse paths must be composed the same way (as a node or as connected segments) for each path. On single digitized roads, the forward and reverse locations must be the same node or the same series of connected segments.

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TMC Information – TMC Locations and Paths

Examples of locations:

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Bridge Limited highway access points

Tollbooth County Border

path

location

Reverse

Forward

1 2 32 3

21

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TMC Information – Location Compositions

A. In general, Locations are composed of all the segments at an intersection.1. This will include the segments between ramp structures, slip roads, and double

digitized intersections as well as those segments that make up a traffic circle.

2. This does NOT include segments in between connector segments such as for U-Turns or Michigan Lefts.

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Fig. 1 Fig. 2

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3. For single digitized roads, forward and reverse path information are on opposite sides of the same segments. The locations are required to be equal.

B. Simple Intersections are composed at a single node for single digitized roads or two nodes for double digitized roads. The node of intersection may be a grade level crossing or may not be a grade level crossing.

1. Where the location is not at the end of a path, the segment ends on either side of the location determine this node.

2. Where the location is at the end of a path, only the segment end that belongs to a segment on the path is included.

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Fig. 6

Fig. 3 Fig. 4

Fig. 5

Fig. 7 Fig. 8

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C. Where there is an incomplete intersection, the location occurs between existing ramps/slip roads and the point of intersection (at grade, or not at grade) with the cross-street or ramp.

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As in Fig.12, other streets may exist, crossing at grade or not at grade, in between the location ramp and cross street. These do not impact the location composition.

Fig. 9Fig. 10

Fig. 11

Fig. 12

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D. Asymmetrical locations require like compositions. 1. Forward and Reverse paths may contain the same real world reference, but be offset from

each other.

2. Even if the Forward and Reverse paths do not contain the same real world objects, both paths require a corresponding location that is as near opposite as possible.

3. When asymmetrical intersections can justifiably be composed as either segments or nodes, segments are preferred unless the only available segments extend unreasonably beyond the actual real world location. For the path with the simple intersection, the segment just ahead (in the direction of the path) of the junction is used for the location.

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Rest Area

Rest Area

Fig. 13

Fig. 14Fig. 15

Fig. 16

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4. On single digitized roads, the locations must be contiguous, even if the real world objects they describe are not.

E. Locations may overlap or nest. When this occurs, each individual location uses the same composition rules as non-overlapping compositions. Any duplicate location (those which describes the same real-world object) will overlap each other.

1. Complex highway interchanges will often result in multiple overlapping compositions.

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Rest Area

Rest Area

Fig. 17Fig. 18

Fig. 19 Fig. 20

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2. Node type locations can overlap. This often occurs at county or State borders where there may be duplicate locations for the same real world object.

3. Locations composed of nodes can nest inside locations composed of segments. This could occur where one location describes a road accessible through a defined ramp structure, and the second location describes a road that crosses in the ramp structure (at grade or at a separated grade), but has no ramp structure.

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Note: There are also areas of the country where a portion of road crosses a border many times and the path may define several border locations (e.g. where the border is at a meandering river). These are not overlapping compositions, but sequential and would be chained normally.

Fig. 21

Fig.22

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F. Paths may follow a numbered highway or named road that changes direction at an intersection. Locations at such changes in direction should be composed on the named roads referenced by the TMC Master Table.

1. If elevations are present, turn channels and slip roads that are used by traffic to follow a path are utilized to create the location.

2. If elevations are not present, turn channels & slip roads are used unless this would create a valance 3+ TMC Path. This rule should be followed regardless of maneuvers or other routing attributes that may prevent the line of travel.

3. Where a path changes direction at a simple intersection, the location of that intersection is composed as a node.

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Fig. 23

Fig. 24 Fig. 25 Fig. 26

Fig. 27

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4. Dual-Carriageway / dual-carriageway intersections with no turn channels or slip roads are composed on nodes.

G. Where a location is at the end of a path, the following is taken into consideration.1. If the location is at the end of the highway, the location will end where the named highway

ends without utilizing any ramp structures. If this portion of the road is within ramps, then segments are utilized (Figure 29). If this is before any ramps, then nodes are utilized (Figure 30).

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Point at which named highway ends.

Fig. 29 Fig. 30

Fig. 28

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2. If the path ends, but the highway or named road that describes the path continues, the location will include those named road segments or ramps at the intersection necessary to continue on the same named road.

H. Locations at Traffic Circles1. Where a location exists on a traffic circle that is not at the start or end of a TMC Path the

location is composed of the road elements/segments on the traffic circle. Node type locations are not allowed.

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Fig. 32Fig. 31

Continuation of highest-level highway named in the path.

Fig. 33

Fig. 34 Fig. 35

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2. Where the first or last location of a TMC path is at a traffic, that location is composed of the nodes where the path starts/ends at the traffic circle.

I. Locations at Y IntersectionsWhere a location exists at a Y intersection the full extent of the Y ‘arms’ should be used to construct the location.

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Fig. 36 Fig. 37

Fig. 38

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J. Locations and Parallel Roads

Where the TMC locations are physically separated from access to the described cross street, by a Parallel road, approximate location composition may be used. These cases occurs where

– The location is composed along an HOV lane and access is limited to that of the main highway; or

– the location is composed along a main highway but access is limited by extented frontage road structures.

At the beginning or ending of the parallel road, if direct access to the location is within about 1/3 of a mile, location composition approximation is not applied.

1. Approximation is created by composing at the most near opposite set of segments to where the location would be composed if access to the described location were direct.

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Fig. 39b: Location approximation not applied at the start or end of parallel road structure where direct access is less than .5 km.

Fig. 39a Location approximation

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2. Where an HOV or express lane is represented as a single digitized road (e.g. for reversible lanes), the same rules of equality apply as for other single-digitized roads.

K. Bridges and Tunnels (“Brunnels”) are composed as segments along the entire Brunnel.1. There are often two locations representing the Brunnel, these will be represented as

identical overlapping compositions.

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Fig. 40

Fig. 41

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2. If there exist any locations describing entities on the Brunnel (e.g. toll booth, mid-span point, political boundary), this will be represented as a location nested in the actual Brunnel location(s).

L. Missing Geometry1. At those locations where the database is missing geometry that would be captured

regardless of the existence of a TMC location, that geometry should be added and attributed before the application of TMC location information according to all existing modeling specs and editing guidelines.

2. At those locations where the database topology or geometry is found to be in error and this error is interfering with the ability to compose a TMC location correctly, that geometry should be altered according to all existing modeling specs and editing guidelines before the application of TMC location information.

3. Where there is missing geometry because a TMC Location describe real-world entities that do not exist (e.g. a planned or demolished highway), that TMC Location information is NOT captured in the database.

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Fig. 42

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TMC Information – TMC Path Composition and chaining

A. Basic Path Chaining1. Segments part of the composition of a location will carry the information for that location.

2. Segments along a path between locations will carry the location information of the next location in the direction of the path. The next location is determined by both the sequence in the TMC Master Table and the physical sequence of locations on the path. Usually the table sequence and physical sequence will be in the same order.

3. Where a location is defined at a node, the segment before the node on the path should carry the information for that location. The segment after the node on the path should carry the information for the next location. Figure 36 illustrates a node as the composition for a location D.

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Fig. 44

C D

D E

D D E E F

C D D E E

Fig. 43

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4. While any path in a single direction will never have forks or branches, when viewed collectively, the forward and reverse paths may form branches where a road toggles between being single digitized and double-digitized.

B. Locations that physically occur on a path in a different order than the sequence shown in the Mater Table are considered non-sequential. Segments along a path containing non-sequential locations will carry the location information for both the next physical location on the path and the information for the next location in the Master Table. The rules are as follows:

1. Every segment between two consecutive locations in the master table must carry the information for the second location in the table.

2. Every segment between two consecutive locations on a path must carry the information for the second location on the path.

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C D E E

D

D

D D E

E E F

Fig. 45

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Figure 46 presumes a Master Table order of C, D, E, F, G. Location D Location F Location E Location G

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C D D (F & D) (F&D) (E& F) (E& F) G

D D (E&F) (E&F) (E&G) (G&E) G G

Fig. 46

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C. Paths along one-way streetsThe path direction should follow the direction of traffic. One-way information may coincide or conflict with the path direction.1. In general, if the path is described by a highway number, any street that has the

highway listed as a primary or alternate name may carry the path.

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D D E E F

C D D E E 1st Ave: Hwy 99

2nd Ave: Hwy 99

Fig. 49

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2. In general, if the path is described by a road name, that street, even if one-way, will carry forward and reverse path information. This will result in a valid exception to any reversibility errors. Note that there will usually be a corresponding, but separate, path that takes traffic in the reverse direction.

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D D E E F

C D D E E 2nd Ave

Fig. 50

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TMC Information – TMC Guidelines

Paths only apply to one roadway, if the path branches off of the correct roadway onto another roadway with a different name, it is an error

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incorrect correct

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It is ok to have overlapping locations and paths. TMC table information can help confirm these overlaps.

Locations must be the same type of composition for both directions (points with points, chains with chains)

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incorrectcorrect

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When a TMC location is at an intersection, it should include the entire area between on and off ramps, but should not extend beyond the ramp structure

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incorrect correct

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When there is an onramp, but no off ramp, or an off ramp but no onramp, the TMC location should end at the next overpass or underpass

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correctincorrect

TMC location ends at the overpass

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Segments between TMC locations should carry the location ID of the next location that makes up the path

Check that the correct location is highlighted when adding paths to ensure that this information is imputed correctly—this has major routing implications

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forward

reverse

1 1 1 2 2

22211

1 1 2 2

2

2

111 2

incorrect correct

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TMC Information – Summing Up

TMCs support real-time traffic information applications In our database, TMCs are made up of locations, and chains of

locations called paths

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TMC Information – Questions

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KEY ASPECTS OF NAVIGATION - TMC Information 1. TMC Information – Overview What are TMCs...

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