California Department of Transportation

Project Development Workflow Tasks (PDWT)

Part 3 - Identify Project Need and Project Initiation Document

II. Project Initiation Document

B. Develop Initial Alternatives (WBS 150.10) - Develop Concept Alternatives (WBS 150.10.15)

P35. Prepare Base Layouts for Concept Geometrics

The Strip Map delineates the project limits, existing details and possible alternatives. The base layout will refine this information, as the concept geometrics are examined. The standard practice is to prepare drawings electronically using the standard engineering software applications approved for use for Roadway Design Engineers. The base layout drawing delineates the project limits, existing roadway edges of pavement, lane lines, and existing right of way. There are several options that a project engineer may consider for preparing a Base Layout.

Use ground survey data.

Use of coordinated survey data is more accurate and can be used later for preparing contract plans. At the PID phase of a project, however, expenditure of resources to obtain a ground survey is not typically allowed. The expenditure of Survey’s resources performing ground surveys on alternatives that may never be constructed is unwise and may contribute to a Survey Office workload problem. Obtaining ground survey data may take many months and is unlikely to fit the delivery schedule of a PID. Obtaining ground surveys for spot improvement projects is a good option. Another option may to obtain existing ground surveys or aerial mapping from previous projects within the project limits. However, any old survey data or mapping must be verified.

Use aerial mapping.

Aerial mapping is a combination of ground control surveys and accurate aerial photography. Obtaining aerial mapping is very costly and may require more than a year to obtain; thus it is a method rarely used for PID phase work. Aerial mapping may be a good option is when the project is very large, such as a new freeway project. Mapping of a large area provides the ability to outline many alternatives with different alignments. This option should only be used if there is sufficient long-lead time available, and management approves of the cost. A digital terrain model (DTM) may be prepared from aerial mapping that may be directly used for preparing construction contract plan.

Scan existing maps, drawings or photos.

Scanning of existing maps, drawings or photos is an economical and fast method of creating a base electronic drawing. The Survey Office and Right of Way Engineering Office may have existing mapping in electronic formats available for importing into design software. Scanned images may not be used for preparing construction contract plans, but is a good option when the delivery schedule is short. Scanned images do not have any coordinate reference, scales may be distorted, and manipulation of the image is very limited. Using scanned photos showing ground features (buildings, waterways, trees, etc.) as a base drawing is particularly beneficial for Preliminary Environmental Study Limits maps, Right of Way Requirement maps, public displays, and PID attachments.

Use Digital Highway Inventory Photography Project (DHIPP) photos.

Digitized Highway Inventory Photos are colored Highway Inventory Photos converted to 2-D digital images. Digitized photo images may be easily manipulated and lend themselves to drafting of project alternatives and use as Preliminary Environmental Study Limits maps, Right of Way Requirement maps, public displays and PID attachments. This is a very sound option for base maps.

Use As-builts and Right of Way Record Maps.

The project engineer may prepare base drawings from As-built and Right of Way records by re-drafting them. This is a commonly used method that yields a very accurate base drawing for Preliminary Environmental Study Limits maps, Right of Way Requirement maps, public displays, PID attachments. These maps may also be used later for preparing contract plans. However, these maps may not be entirely accurate, and they may be based on an old survey datum. Ground survey data may be overlaid later to correct inaccuracies.

Time Constraint:

A single build alternative project may take one to two months. Complex projects (such as new freeways) with multiple concept alternatives may require as much as one year to prepare. The time to scan existing maps, drawings or photos and/or importing digitized highway inventory photos and/or re-drafting base drawings from As-Built and Right of Way record maps is quite extensive and laborious.

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This page last updated Oct. 11, 2010