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Bicycles/Pedestrians

Safety Toolbox: Problem identification

How to analyze

Now that you know what to look for and where to get the data, how are you going to conduct the actual analysis? In this section:

Statistical analysis


Collision rate formulas. To date, there is no widely accepted methodology for calculating collision rates for pedestrian and bicyclist-involved collisions because of the difficulty of obtaining exposure data and the lack of consensus on how to calculate exposure. Factors that may affect exposure include but are not limited to: number of conflicting vehicles, crossing distance and walking speed, presence of sidewalks or refuge islands, the volume of pedestrians, and crosswalk presence and treatments, etc. for pedestrian-involved collisions; and number of conflicting vehicles, bike-oriented markings and signs, presence or absence of on-street parking, the volume of bicyclists, etc. for bicyclist-involved collisions. Keeping in mind these limitations, following are a few methods that may be used to calculate collision rates.

Wide-area comparative collision rate analyses (across cities, counties, regions, states, etc.) may be conducted by using the number of pedestrian or bicyclist-involved collisions over some common time period and dividing that by million population, million vehicle miles of travel, population of people who walk or bike to work, etc.

Comparative analyses of intersections may be conducted by using the number of pedestrian or bicyclist-involved collisions over some common time period and dividing that by million vehicles entering the intersection or million pedestrians/bicyclist entering the intersection or some combination of the two, as illustrated in Katz, Okitsu & Associates' City of Santa Ana Pedestrian Safety Study.

The Surface Transportation Policy Project also developed the "Pedestrian Danger Index", which is the number of fatalities per 100,000 population divided by the percentage of work trips made by walking. A similar calculation may be made with bicyclist data.

Statistical Software Packages. Higher levels of collision analysis may be achieved using commercial statistical software packages such as Microsoft Excel, Microsoft Access, SPSS, and SAS. The simplest of these is Excel, which is the file format in which SWITRS data is typically provided. The higher the capabilities of the software package, the more technical knowledge is required of the analyst. Most of the analyses recommended in this Toolbox may be achieved using Excel. When combined with a spatial analysis, a database such as Microsoft Access, would be required.

Spatial analysis


Pin Maps. A rudimentary form of spatial analysis entails locating collisions on a large map by using color-coded pins. Prior to the advent of GIS, this was the most common tool employed by traffic engineers for conducting spatial analyses.

Geographic Information Systems (GIS). Significantly more robust analyses can be conducted using a GIS: a system for management, analysis, and display of geographic knowledge, which is represented using a series of information sets such as maps and globes, geographic data sets, processing and work flow models, data models, and metadata. Software packages offered by ESRI (ArcXXX Suite) and Caliper Corporation (Maptitude) are among the most common. Use of a GIS requires some technical expertise.

To use a GIS for collision analysis, collisions must be electronically mapped or geocoded. Starting in January 2006, the CHP 555 form will include X-Y coordinates, which should facilitate spatial collision analyses. However, it may take a while before all police/sheriff departments are equipped with the necessary equipment to enter this information as part of the collision reports. Until then, and for all reports prior to January 2006, there will be a need to geocode collisions to enable spatial analysis with a GIS. Most GIS packages come with an automated geocoding service, but some manual manipulation will still be required. See How To Geocode SWITRS Data.

Free tools from FHWA


HSIS Safety Analysis Tools. GIS analysis tools that are specifically tailored to crash analysis, and beyond that, to these pedestrian and bicyclist-involved applications: safe routes for walking to school, selection of streets for bicycle routes, and high pedestrian crash zones. To obtain a copy of the CD, e-mail a request to Carol Tan (carol.tan@dot.gov), HSIS Program Manager.

Pedestrian and Bicyclist Crash Analysis Tool (PBCAT) . A crash typing software developed by the Federal Highway Administration, in cooperation with the National Highway Traffic Safety Administration, to assist planners and engineers in developing a database with specific details of crashes between motor vehicles and pedestrians and/or bicyclists. The crash type of cyclists and pedestrians describes the pre-crash actions of the parties involved and the series of events that led to the collision. With the database developed, the software can be used to produce reports and select countermeasures to address the problems identified.

Analysis of crash type data can provide information on where pedestrian and bicyclist crashes occur (city, street, intersection, two-lane road, etc.), when they occur (time of day, day of week, etc.), and characteristics of the victims involved (age, gender, injury severity, etc.). The data can provide a sufficient level of detail regarding the sequence of events leading to the crash.

Countermeasures for bicycle and pedestrian crash types are included in the database. Countermeasures are suggestions for design, safety and education. Reporting and analysis include summaries of variables in crash type and the ability to cross tabulate variables.

The software is distributed for free from the Pedestrian and Bicycle Information Center website: http://www.walkinginfo.org/pc/pbcat.htm

Custom collision analysis software


Accident Information Management System (AIMS). A modular collision analysis software that works with or without a GIS and is customizable for any type of database. Provides capability for plotting collisions in three dimensions. Prices start at about $4,000. Contact Information: JMW Engineering, 5562 Caithness Court, Fairfax VA, 703.503.3219.

Crash Magic. See Intersection Magic below.

Crossroads. A traffic collision database and analysis software that is commonly used in agencies in the Bay Area for tracking and reporting collisions and citations including bicycle and pedestrian-involved. This system is used by an agency alone or in conjunction with SWITRS data. Once the data is entered into the system, queries by location, primary collision factor, collision type, reporting district, highest degree of injury, and other factors can be generated.

Technical assistance from Crossroads Software is available to import collision data and geocode collision locations. Data can be used to identify collisions by type, severity, time and days. A GIS component allows maps to be created showing user-defined queries of various types of collisions at any point in the street network. The GIS database queries not only by street name and intersection but also by distances from intersections or landmarks. A traffic count management system is built into the software for calculating collision rates.

Systems start in the $40,000 range, which includes SWITRS data and GIS data. Historically, the purchase and set-up of Crossroads has been eligible for funding under Office of Traffic Safety grants. Contact Information: Crossroads Software, 210 West Birch St. Suite 207, Brea CA 92821, 714-990-6433.

Custom Crime Reporting Solutions (CCRS). Various custom software packages designed specifically for law enforcement agencies, including a traffic collision software package called TRS2000, which tracks both citation and collision information, and is specifically designed for State of California procedures. Contact: ccrsinc@earthlink.net.

Highway Safety Analysis (HSA) Software. Organizes crash data by categories, types, and locations. Includes capabilities for generating collision diagrams and various analytical charts. Works with Microsoft Access database, but is customizable for other types of databases. Prices start at around $700. Contact: X32 Group, 119 Yorkshire Drive, Morganville NJ, 917.691.7524.

Intersection Magic, Crash Magic and Map Magic. Intersection Magic is a data summary software package for collision analysis of intersections. Offers detailed automated collision diagrams, data retrieval, accident summaries and statistical output.

Map Magic, a GIS feature that ties to Arcview, can generate pin maps to show collisions in a given time period, pedestrian or bicycle collisions, severity of collision, type, number, etc over the existing roadway network using another software module that ties into Intersection Magic.

Users can customize their own schematics for intersections. Clicking on the collision diagram can retrieve accident information. Like accidents can be shown with a single graphic. This data can be generated from an agency's own collision information or by importing SWITRS data into the database.

Crash Magic is available in desktop and on-line versions, and is the successor to Intersection Magic.

Intersection Magic and Map Magic start at $2,500 and go up commensurate to the size of the jurisdiction. Crash Magic starts at $3,500 and also go up commensurate to the size of the jurisdiction. Contact Information: Pd' Programming, Inc., 725 Aegean Drive, Lafayette, CO 80026, (888) PD-MAGIC.

Field audits

You've done a lot of office work calling people to get the data, crunching the numbers, creating charts and graphs, and you've identified some problem areas. The next thing to do is to go the scene to verify your findings.