Safety Analyst Data Dictionary

CDDP

Commission for drunk driving prevention.

CRS

Crash reporting system.

Network screening

Process of identifying and ranking high crash locations from highway network.

Network Element

Intersections, roadway segments, routes, combination of roadway segments and intersections aka facility, ramps rail-road crossings, etc from the network elements.

Profile Management

The process of creating the network (user-defined scope) to be used for further analysis is termed as profile management.

Sliding window

In the sliding window a window of specified length is conceptually moved along the network element chosen by the user from beginning mile-post to end mile-post in increments of a specified length. The window spans over multiple roadway segment.

Peak Search

In peak searching technique the routes are segmented based on some user defined length. Each segment is then sub-divided based on a user defined window length. Performance measures are calculated at the sub-segment levels along with the individual coefficient of variation.

Simple Ranking

In simple ranking technique the routes are segmented based on the user defined length. Performance measures are calculated at the segment level which represents the overall safety status. Therefore, further segmentation (i.e. sub-segments) is not implemented for the simple ranking technique.

Main Profile locations

Main locations are the locations of the segments into which a section of roadway is divided into segments that are non-overlapping.

Secondary Profile locations

For the Sliding Window or peak search method, the main locations are further segmented into sub-segments to facilitate the screening process. These locations are also known as “Secondary Locations”. The secondary locations can be considered as the “window positions” into which the section is divided for peak search or sliding window techniques. For peak search technique the window positions are fixed and non-overlapping (no window step or window step=0). For sliding window the window positions can be varied by changing the window step.

Sliding Window Length

The window length used for secondary profile locations is termed as sliding window length.

Sliding Window Step

The length used for increment from first window to another is termed as sliding window step.

Crash filter

Crash filter is a filter applied to the crash database to select a subset of crashes in safety analysis. Crash filter is often designed to fit with a targeted safety program. For example: if implementation of rumble strips is contemplated as a potential safety intervention, the pertinent crash filter could be roadway departure crash or crashes due to driver’s distraction. Similarly, for DUI prevention program crash filter could be crashes with alcohol involvement. 

Performance measure

A performance measure is composed of a number and a unit of measure. In Safety Management System, some of the performance measures are crash rates (number of crashes/volume), frequency of crashes etc.  

Coefficient-of-Variation

The ratio of the standard deviation to the mean.

Threshold Handle

Threshold Handle Rules define the mechanism of computing, storing and

Term

Definition

Rules

utilizing threshold during a particular screening.

CMF

Crash-modification factors (CMF) is a multiplicative factor used to compute the expected number of crashes after implementing a given countermeasure at a specific site.

CRF

Crash Reduction factor (CRF)  is the percentage crash reduction that might be expected after implementing a given countermeasure at a specific site.

Bid Items

Bid items data include the average unit bid prices for the most current years.

Treatments

The countermeasures applied to the location are termed as treatment.

EUAC

Equivalent uniform annual costs.

EUAB

Equivalent uniform annual benefits.

Est. Benefit/Cost

The ratio of EUAB/EUAC.