An Overview of the Chester CountyLocal Linear Referencing System (LRS)

What is an LRS?

Most generally, a linear referencing system comprises:

1) Selected linear features of an agency’s centerline aggregated into routes that represent distinct paths where travel can, does or will occur.

For the regional GIS-T the focus is existing street centerline

2) Measure values (in feet for the PA regional GIS-T) applied along these routes – consistently ascending from one end to the other and no redundancy.

3) Linear or point representations of Spatial and/or Attribute data related to these routes and measures; referenced by event tables.

Evaluation and Preparation of thepre-local LRS Centerline File

Chester County non-local LRS transportation centerline (TCL):

1. “Native” County Centerline (CL) consists of street (and limited trail) segmented and attributed according to requirements of emergency services and addressing. Spatially accurate with a few known exceptions.

2. Digitized direction of segments runs with increasing addresses (or travel direction on dual-centerline freeway) Ramps generally not part of native ChesCo CL: added to TCL

3. TCL maintained as network – with Junctions feature class (FC) – in feature dataset.

4. Native ChesCo CL – and now TCL – verified as 100% topologically correct (according to rules elsewhere described).

Chester County non-local LRS TCL Example # 1:PennDOT LRS supported on spatially accurate ChesCo CL, TCL includes all public roads and ties to County data.

Pre-local LRS File Evaluation and Preparation (cont.)

Step 2: Assignment of segments to routes cont

Example of correct route definition (route color by local route ID)

In contrast to the muni-line road illustrated on the previous slide, Berwyn Paoli Rd must change route ID because Tredyffrin has the higher PennDOT code.

Step 2: Assignment of segments to routes cont

Example of correct route definition (muni-line roads)

Same name & muni, but not continuous

Directional Prefix change

Step 2: Assignment of segments to routes cont

Example of correct route definition: reasons for breaking routes

Six segments named Esprit TC No more than four can be strung together to form a route Several options for route definition Best (?) solution leaves two single standalone segment routes (other “correct” options are possible)

Subjective Route Definition ChoiceWhen same-name/same muni streets intersect

Step 2: Assignment of segments to routes cont

Option 5

Option 2

Option 3

Option 4

Option 1(selected

)

There is no need to waste time analyzing the comparative merits of one route definition over another. Just make sure your method produces a result that is acceptable by the route-definition rules.

Step 2: Assignment of segments to routes cont

Examples of route definition and Route Names/ID’s

Step 2: Assignment of segments to routes cont

Example of route definition and measure for routes that begin and/or end with a loop segment.

Route-data Table(s), ID’s and Attributes

A master route table(s) for all routes (local, PennDOT …)

1) Ensures that all route ID’s are unique and valid;

2) Maintains referential integrity with regard to segments’ route attributes;

3) Lets you join centerline segments to their route data.

The Transportation Centerline feature class table includes fields for all possible route ID’s

Example of application of M-Values to Route Step 2: Assignment of segments to routes: suggested procedure

West Bradford’s Vermont Lane Route: Two segments – approx. 505’ Route runs EB, but Westernmost segment runs WB

Multiple LRS optionsSupported by single underlying geometry

Single “Transportation

Centerline” Feature Class

PennDOT LRS Applied Local LRS Applied Other LRS Applied

• Rail station, mile marker, other agency measures, etc:

• All Linearly-referenced data transformable among LRS’s via common underlying geometry/ArcToolbox

Hybrid LRS Applied?

1) Fully-segmented, all inclusive FC (allows segment-specific event reference)

2) FC “dissolved” by applicable route ID’s after definition query is applied to extract only relevant segments (provides better performance)

OR

Multiple LRS optionsSupported by single underlying geometry

Single “Transportation

Centerline” Feature Class

PennDOT LRS Applied Local LRS Applied

PennDOT measures by NLF

Local measures by local Route ID

Local vs. PennDOT LRS on Same Centerline

• Routes Start in same place and run in same direction• M-values on both LRS’s are close through West Chester• New Local Route 52_0036 begins at municipal line, where as PennDOT NLF 2907 continues

Local vs. PennDOT LRS ramps and divided highway

http://www.dot7.state.pa.us/ividlog/video_locate.asp

Local Routes: Not just for streets• Rail (active, inactive, abandoned…)

• Non-motorized path (trail, multi-use path, etc)

• Waterway (navigable/for recreation)

• Inactive corridors (utility ROW’s, muni easements, railbanking …)

Using the local LRSExample of route event source

Using the local LRSExample of route event generation with custom application

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