Crash Diagram

Overview

The Crash Diagram tool generates an interactive crash diagram from a crash selection in the SWITRS GIS Map. After you spatially select crashes (learn how), choose Create Crash Diagram from the Results panel to open the diagram workspace. This guide explains each panel and walks through a detailed tutorial.

Understand the interface

Crash Diagram information panel

The information panel on the left houses map information, the legend, a mapping summary, and crash filtering controls. Collapse it with Hide to maximize map space, or restore it with Show Menu.

Map canvas

The map displays crash symbols, added layers, and any drawing tools. Hide the panel to focus on the map.

Map toolbar

The toolbar below the map adjusts opacity, icon size, basemap options, and label visibility. You'll use it frequently while refining diagrams.

Information panel tools

Use the panel to configure print output, review data summaries, and filter the map.

Print preview

Select Print Preview to enter a ready-to-print layout. Pan or zoom the map as needed, then choose Print or exit to make more edits.

Map information

Document the primary and secondary streets, time period, and agency. These fields are included in the printout.

Legend

The legend lists party movements on the left and pedestrians, bicyclists, objects, and crashes on the right.

Mapping summary

Monitor how many crashes were mapped successfully and whether any remain undrawn (often because of missing movement data or more than two parties).

Crash filtering

Toggle crash types to highlight relevant crashes while editing the map.

Work with the map

Beyond displaying selected crashes, the map lets you add, move, or edit crashes to refine the diagram.

Add crashes

Right-click a location, populate severity, type, and party information, and select Add to place a new crash.

Edit crashes

Right-click an existing crash to rotate symbols or remove it. Summaries update automatically.

Move crashes

Select a crash symbol, drag it to a new location, and release to reposition it.

View crash details

Click a crash to review party data, crash type, and offsets before making edits.

Adjust the map display

The map toolbar customizes the basemap and symbol visibility. All controls are available with the default Map basemap; Satellite mode supports opacity and icon adjustments.

Map opacity

Slide the opacity control to highlight symbols, especially when using Satellite imagery.

Icon size

Use the icon size control to enlarge or shrink crash symbols for readability.

Street names and landmarks

Toggle street names and landmarks for additional context when using the Map basemap.

Grayscale mode

Enable grayscale to convert the basemap to black and white.

Step-by-step tutorial

Scenario: Build a crash diagram for the intersection of University Avenue and Shattuck Avenue in Berkeley, focusing on head-on and rear-end crashes involving straight-moving vehicles.

1. Query SWITRS GIS Map

Set the following filters in SWITRS GIS Map. If you're new to the tool, review the GIS Map user guide.

• Time frame: 03-01-2018 to 09-01-2018
• County: Alameda
• City: Berkeley
• Crash factor: Type of Crash = Head-On and Rear End
• Party factor: Movement Preceding Crash = Proceeding Straight
• Victim factor: Party Number = 0 to 2

2. Spatially select the crashes

Select the eight relevant crashes around the intersection, then choose Create Crash Diagram from the Results panel.

3. Complete map information

Fill in Map Information with:

• Primary Street: University Ave
• Secondary Street: Shattuck Ave
• Time Period: 03-01-2018 to 09-01-2018
• Agency Name: SafeTREC

Notice any unmapped crashes in the summary. You can refine the diagram or print it as-is.

4. Check for overlapped crashes

Note Compare the number of map symbols to the mapped crash count. Mismatches often indicate overlaps.

Look for single symbols surrounded by multiple arrows or pedestrian icons. These likely represent overlapping crashes.

5. Adjust crash placement

To analyze environmental factors, reposition crashes to precise lanes or crosswalks.

Example: Kittredge Street and Oxford Street

1. Toggle Street Names in the toolbar to see road labels.
2. Open Crash Details to confirm party movements (northbound vehicle turning left, pedestrian proceeding straight).
3. Switch to the Satellite basemap and adjust opacity for lane markings.
4. Drag the crash symbol into the appropriate left-turn lane based on the details.

6. Rotate crashes to match traffic flow

Example: University Avenue and Walnut Street

1. Open Crash Details to verify direction.
2. Drag the crash to the appropriate lane using offset information.
3. Right-click the symbol and rotate it until vehicle icons align with travel direction.

7. Add undrawn crashes

1. Identify crashes marked as Not Drawn in the mapping summary and download crash data from SWITRS GIS Map.
2. Compare Case IDs to locate missing crashes (e.g., case #5147031).
3. Download the parties file without party/victim filters to gather all parties.
4. Use SWITRS codebooks to translate values for severity, type, movements, direction, and party type.
5. Analyze the data to infer missing directions. In this example, both parties faced east even though Party 1 direction was unknown, explaining why the crash was not drawn.
6. Add the crash manually, accounting for offset distance and direction (101 feet east of University Ave and Grant St.).

8. Print the final diagram

Open Print Preview, adjust the map extent, and print or save as PDF. The example below shows the final layout after moving and rotating all eight crashes.