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 (150.10) - Develop Concept Alternatives (WBS 150.10.15)

P44. Request Safety Index Calculation

A Safety Index (SI) is a benefit/cost ratio analysis (calculation) of a proposed improvement. It is a measure of the accident cost saved by motorists expressed as a percentage of the capital cost of the improvement. A Safety Index calculation is required for spot improvements and for traffic safety improvement projects when reduction of accidents is a significant goal of the project. Examples of safety improvements that require a SI include: general spot improvements, signing, channelizations, safety lighting, truck escape ramps, climbing lanes, median barrier upgrades, left turn lanes, rumble strips, auxiliary lanes, shoulder widening, wet pavement correction, traffic signals, round-a-bouts, and curve corrections. Safety improvement projects are triggered when the SI is at least 200, meaning the benefit (dollar value of total accident savings to motorists over the project life) is at least twice the cost of constructing the project. Projects that have a less than 200 lack sufficient justifications as a safety project however, the project may meet justifications for operational improvements based on a delay index. See the "Request Delay Index" task.

The project engineer requests and obtains a SI calculation from the District Traffic Operations Branch. The project engineer must include with the request: project limits, type of project and description of proposed improvements, Design Designation, and the estimated total project construction costs.

Operational Improvement projects require justification based on a Priority Index Number (PIN). A PIN is based on both a Safety Index and a Delay Index. If not already identified, the project engineers must obtain SI and DI calculations from the appropriate offices and should not perform their own calculations.

Projects that are based on SI alone qualify as Safety Improvement projects and must maintain a SI of 200 or more up through the submittal of PS&E to headquarters. At the PID phase a minimum of 230 is recommended to allow for cost adjustments. If project construction costs increase after the original SI calculation, a revised SI must be obtained. For this reason, care should be taken to exclude items of work not essential to a safety-related project. For example, District Hydraulics or Maintenance may recommend rehabilitation of culverts at the project location. However, this may not be vital to the safety of the motorist, raise project construction costs, and lower the SI. When the SI falls below the threshold, the project may potentially be delayed.

References:

Traffic Safety Guidelines, (Chapter 5, “Traffic Safety Index)


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If you have any questions about the Project Development Procedures Manual send e-mail to:charles.olson@dot.ca.gov

This page last updated October 20, 2010