Skip to end of metadata
Go to start of metadata


Contents


The DDOT Centerline



In a Linear Referencing System (or LRS), routes are the geographic representation of a roadway.  DDOT uses route centerlines for maintaining linearly referenced data about the roadway.  This means that most characteristics about the roadway (number of lanes, surface type, median type present, etc) are stored in related tables with a reference (using the RouteID) to a given route.  DDOT and most transportation agencies avoid adding these characteristics as direct table attributes on centerline.  

Why Linear Referencing?

The power of linear references allows us to keep the centerline isolated from any attribute changes.  Why is this important? In typical GIS editing, a change in any attribute for a feature will require the user to split the feature where the change begins (think of when a road goes from 2 lanes to 4 lanes). Imagine how many segment breaks we would have if Lanes, Material, Speed and Quality were all attributes maintained on a centerline feature class.

In the graphic below, there are several changes which take place along the roadway. Linear referencing allows us to store the attributes in separate tables leaving us free to change/update the data about the roadway- without breaking the centerline every time a change is needed. Pretty cool, eh? (smile)


Multiple sets of attributes for road features

From ESRI's What is Linear Referencing?.

The New Centerline Management System

We have transitioned to a modern centerline maintenance platform called ESRI Roads and Highways.  Although this change comes with a lot of exciting new features and capabilities, one of the downsides is that we will no longer maintain certain legacy data.  Below are a listing of items which will will be managed differently or will no longer be maintained by DDOT after  :

If you currently use...We recommend changing to...
Street SegmentsBlocks
Roadway SegmentsSubBlocks

What about street codes?

Unfortunately, the Street Code table will no longer maintained by DDOT.  Moving forward, we recommend you utilize the 'RouteID' field, which is found in our centerline Routes table.  This will provide an equivalent unique ID for a given roadway.  

Routes (Roadway network)

Routes are typically unbroken geometries..  

FIELDDESCRIPTIONDATA TYPEEXAMPLE
FROMDATE

Active/start date of a route record

Date9/1/2018
TODATERetired date of a route recordDate9/1/2018
ROUTEID*Unique ID of a route (a linear LRS feature)Text11001402
ROUTENAME+Name of a route in the LRS. Concatenated from StreetName + StreetType + QuadrantText14th ST NW
STREETNAMEStreet name of this route (if RoadType = Street or Alley)Text14th
STREETTYPEStreet type of this route (if RoadType = Street)TextST
QUADRANTQuadrant of this route segment (if RoadType = Street or Alley)Short integerNW
ROADTYPEType of roadway (see domain lookup table)Short Integer1 (Street)

*Key ID

+Calculated Field

WE ARE NO LONGER MAINTAINING A LISTING OF STREET CODE (STCODE) OR STREET IDS (STREETID)


ROADTYPE codes

CodeDescription
1Street
2Service Road
3Ramp
4Alley
5

Drivewa

6Trail

QUADRANT codes

CodeDescription
1NW
2NE
3SE
4SW
5

BN


How is a RouteID Created?

Our route identifiers are mostly random, 8 or 9 character values which represent the unique route feature within a given quadrant.


First Digit = RoadType Code

= Street

2 = Service Road

3 = Ramp 

4 = Alley  

5 = Driveway

6 = Trail

Second Digit = Quadrant code:

1 – NW

2 – NE 

3 – SE

4 – SW

5 - Boundary

  • Remaining 6 digits = Script-generated, randomized and unique numbers


Blocks 


PREVIOUSLY CALLED STREET SEGMENTS

For a city, street blocks are a very common way in which to organize and relate work (e.g. 'I need to fix a pothole on the 1600 Block of Pennsylvania Ave'). Although driveways or alleys may intersect streets, this representation requires that the segment remain unbroken.  

Road Types included:

  • Streets

Segmentation Rules: 

  • Only Streets can break/segment other streets.
  • Only At-grade type intersections are respected in this segmentation.  See below for more information 

Fig 3. Block Segment representation


Attributes for Blocks

FIELDDESCRIPTIONDATA TYPEEXAMPLE

StreetSegID

TEMPORARY FIELD

The old ID of this segmentLong Integer

10385

WE ARE CURRENTLY USING THIS FIELD FOR INTERNAL MIGRATION ONLY. ONCE PUBLISHED, USE 'BLOCKID' FOR UNIQUE IDENTIFIER

FromDateWhen this segment was createdDate1/1/2014
ToDateWhen this segment will expireDate<Null>
EventIDUnique randomly generated IDGuid
{962C2785-EE57-4B19-AEE9-D18CB5C30870}
RouteIDUnique ID of the route that this segment is onText11000202
FromMeasureThe measure along the route that this segment begins (meters)Double0
ToMeasureThe measure along the route that this segment ends (meters)Double148.683739
RouteNameName of the route on which this segment existsText2ND ST NW
SegmentTypeThe type of segmentShort Integer2 (Regular Single Centerline)
FromStreetName of streets that intersect the beginning of this segmentTextCONSTITUTION AVE NW
ToStreetName of streets that intersect the end of this segmentTextE ST NW/MITCH SNYDER PL NW
FromIntersectionID of intersection from which this segment beginsText11000202_11025352A
ToIntersectionID of intersection from which this segment endsText11000202_11031332_11061392

BlockID*

Key ID for the block; it is a concatenation of the RouteID, FromIntersectionID and ToIntersectionIDText11000202-11000202_11025352A-11000202_11031332_11061392
BlockKey*Primary key ID for the block. This is a GUID, which is derived from the BlockID valueGUID053c6863e95d1ca3401417cc1adc090d
FromIntersectionKey*Primary key ID for the From Intersection. This is a GUID, derived from FromIntersectionIDGUID8d9cf8ca94fc3048d095388d8d3621f6
ToIntersectionKey*Primary key ID for the To Intersection. This is a GUID, derived from ToIntersectionIDGUID4c68cea7e58591b579fd074bcdaff740
Directionality*Directionality of block (One way digitizing direction, one way against digitizing, two way)Short Integer1 [One way (Digitizing direction)]
created_userThe user that created the segmentSYS GENERATED<Null>
created_dateThe date the segment was createdSYS GENERATED<Null>
last_edited_userThe last user that made edits to this segmentSYS GENERATED<Null>
last_edited_dateThe date the segment was last editedSYS GENERATED<Null>
SHAPE_lengthLength of segmentSYS GENERATED<Null>

NOTE THAT THERE ARE NO FROM/TO ADDRESS FIELDS. WE WILL NOT BE MAINTAINING THEM IN OUR DATA

WE WILL NOT BE GENERATING A 'STREETNAME' LIST


SubBlock 


PREVIOUSLY CALLED ROADWAY SEGMENTS

SubBlock represent the near-full extent of our centerline network (only driveways are excluded).  SubBlock is the finest grained, 'base' segments from which all other segmentation patterns can be constructed (including Blocks).  SubBlock is the original source features for our DDOT Street Centerlines data

Road Types included:

  • Streets
  • Alleys
  • Ramps
  • Service Roads
  • Trails

Segmentation Rules: 

  • Streets, alleys, ramps, service roads and trails can break all others of the same time.
  • At-grade type intersections are respected in this segmentation.  See below for more information 

Fig 2. SubBlock Segment representation


Attributes for SubBlocks

FIELDDESCRIPTIONDATA TYPEEXAMPLE
RouteIDUnique ID of the route that this segment is onText11037052
RouteNameName of the route that this segment is onTextFORT DR NW

SubBlockID*

Intelligent key ID for the sub-block; concatenation of the RouteID, FromIntersectionID and ToIntersectionIDText

11037052-11009492_11037052-11017482_11037052

SubBlockKey*Primary key ID for the subblock. This is a GUID, which is derived from the SubBlockID valueGUID16be813afac223d1e02d0deb9fba6c42
FromMeasureThe measure along the route that this segment beginsFloat135.291
ToMeasureThe measure along the route that this segment endsFloat329.825012
FromIntersectionIDThe ID of the intersection from which this segment beginsText11009492_11037052
ToIntersectionIDThe ID of the intersection at which this segment endsText11017482_11037052
FromIntersectionKey*Primary key ID for the From Intersection. This is a GUID, derived from FromIntersectionIDGUID82b9ad20d7eb65bb5dc336d7223bd061
ToIntersectionKey*Primary key ID for the To Intersection. This is a GUID, derived from ToIntersectionIDGUID55840779f58a725ae98a586b11156d06
FromSubBlock*Name of SubBlocks that intersect the beginning of this segmentTextALBEMARLE ST NW
ToSubBlock*Name of SubBlocks that intersect the end of this segmentTextBRANDYWINE ST NW
Directionality*Directionality of block (One way digitizing direction, one way against digitizing, two way)Short Integer1, One Way (Digitizing direction)
RoadTypeThe type of roadway it is (Street, Alley, Driveway, etc.)TextStreet
BlockIDThe BlockID of the block wherein this sub-block existsText11037052-11009492_11037052-11017482_11037052
BlockKey*Primary key ID for the block. This is a GUID, which is derived from the BlockID valueGUID16be813afac223d1e02d0deb9fba6c42

RoadwaySegID

TEMPORARY FIELD

The old ID of this segmentText

2917

WE ARE CURRENTLY USING THIS FIELD FOR INTERNAL MIGRATION ONLY. ONCE PUBLISHED, USE 'SUBBLOCKID' FOR UNIQUE IDENTIFIER

Intersections 

SubBlock Intersections 

Block Intersections

Roads and Highways manages intersections, however they are not singular points; RH creates a series of points - one for each intersecting road at that intersection.  For DDOT, it is more useful to have a single intersection point representing the intersection.  Through a custom DDOT script,the series of intersection points is reduced into a single representative point.  


Fig 1. Intersection representation


Attributes for Intersections

FIELD

DESCRIPTION

DATA TYPE

EXAMPLE

IntersectionID

Unique ID created by concatenating the ROUTEIDs that make up the intersection

Text

11077672_11094052

IntersectionName

Name of the intersection

Text

S ST NW & WISCONSIN AVE NW

IntersectionKey*Primary key ID for the intersection. This is a GUID, which is derived from the IntersectionID valueGUID13, Signalized, Ped signal
GradeThe type of intersection. For more information, check out the Intersection Grade Codes table below.Short Integer0b56ed21fdb94cea77bf609468b67886

IntersectionRoutes



IntersectionRoutes is a 1-to-many related table to Intersections.  For each Intersection, IntersectionRoutes contains 2 or more records for every intersecting route occurring at that location.

Attributes for IntersectionRoutes

FIELD

DESCRIPTION

DATA TYPE

EXAMPLE

IntersectionID

Unique ID created by concatenating the ROUTEIDs that make up the intersection

Text

11048422_47053562

RouteID

Name of the intersection

Text

INGRAHAM ST NW & Alley-47053562

MeasureThe type of intersection. For more information, check out the Intersection Grade Codes table below.

Intersection Grade Codes

CodeDescriptionComments
0

At Grade TEMPORARY VALUE

Generic code for indicating that the roads at this point intersect each other.
1

Not at Grade

Not at Grade is an overpass/underpass situation where the roads don't connect.
2UndefinedNot currently defined/categorized
10UncontrolledIntersection without signal or signs to stop traffic flow
11Two-way stopOne roadway is allowed to pass without stopping
12All-way stopAll roadways are required to stop before proceeding
13Signalized, Ped signal
14Signalized, No Ped Signal
15RR crossing, Signalized
16RR crossing, Signs Only
17Yield Sign

How is the Centerline Used?


Crash Data



Each crash is automatically referenced upon our LRS, providing a valuable link to all the centerline attribution (AADT, roadway lanes, speed limit, etc). 



Safety Data

In addition to the crash data, the DDOT GIS team auto-generates roadway safety data in support of FHWA's Model Inventory of Roadway Elements (MIRE) 2.0 safety data standards.

The safety data is derived directly from our LRS and is linked directly to the same network as our crash data and our roadway inventory.


Navigation / Accessibility

Interested in performing an accessibility analysis? Doing a Level of Traffic Stress (LTS) analysis? Using Network Analysis in GIS?

Centerline features from our LRS are the primary source for the network. COMING SOON (2019)



Roadway Characteristics

DDOT's GIS team maintains nearly 100 roadway characteristics along the centerline. Many of these are the HPMS roadway attributes, but there are many more.

  • No labels