The Collision Diagram tool allows users to generate an interactive collision diagram. To access the tool, select a set of collisions in SWITRS GIS Map (for help in spatially selecting collisions, see here). Next, click on the link to Create Collision Diagram that should now be included in the Results box. This user guide will go over the Collision Diagram tool's features as well as a step-by-step tutorial.

Page Layout

1. Collision Diagram Information Panel

The Collision Diagram Information Panel is located on the left side of the window. This panel can be minimized by clicking the Hide button near the top. To unhide the panel, click Show Menu in the toolbar on the left. This panel contains Map Information (expanded by default), a Legend, a Mapping Summary, and Collision Filtering. Click on a title bar to expand or collapse its menu. You can also Print Preview the collision diagram, and from the subsequent page, Print the diagram.

2. Map

The Map is the main pane of the Collision Diagram tool. This is where the collision symbols and other layers are displayed. The map can be maximized by hiding the Collision Diagram Information panel.

3. Map Toolbar

Use the Map Toolbar at the bottom of the window to customize the appearance of the map. You can adjust the map opacity and icon size; you can also toggle the street names, landmarks and grayscale for the map background.

1. Collision Diagram Panel

Print Preview

If you want to print the diagram, click the Print Preview button in the top-right corner of the information panel.

The print preview window is preset to a regular 8.5 x 11 inch portrait view. The map information, mapping summary, and legend are displayed at the top of the page. The map shows the symbols for the collisions you had selected. You can also adjust the map view by panning and zooming in/out on the map. To go back to the Collision Diagram tool, click on the Exit Print Preview button. Otherwise, you can now Print the page.

Map Information

In Map Information, you can enter information about the location, time period, and agency in their respected text fields. These will be included in the print-out.


The Legend is a key to all of the symbols used on the map. The symbols on the legend's left side represent a vehicle's movement (or non-movement). On the right are the symbols for pedestrians, bicycles, objects (trees, light poles, etc.), and crashes.

Mapping Summary

The Mapping Summary shows how many of the mapped collisions are Fatal vs. Injury. It also shows the Total number of collisions that were selected (from the SWITRS GIS Map) and the number of these collisions that are Mapped vs. Not Drawn. Collisions are not drawn when there are more than 2 parties involved and/or when parties' movements are not valid (e.g. a collision between two parked cars).

Collision Filtering

Customize the type of collisions to be shown by checking/unchecking the collision types in the Collision Filtering menu.

2. Map

In addition to mapping and filtering the collisions that were selected from the SWTRS GIS Map tool, you can also add collisions that were not geocoded or included in the SWITRS database directly onto the map.

Add Collision

Right-click on a location on the map to add a new collision. In the Add Collision pop-up window, select from the drop-down list of valid options for each type of collision information (Collision Severity, Collision Type, and Party information). Click Add to finish. The new symbol/collision will appear on the map.

Edit Collision

Right-click on a crash symbol (a white or red dot) to rotate or delete the collision from the map. If a collision is deleted, the map summary counts will automatically be updated.

Move a Collision

To move a collision, click on the crash symbol (a white or red dot) and hold and drag it to its new preferred location.

Collision Details

Click on a collision to open its Collision Details pop-up window. Details include the crash's CaseID, general collision details, collision location, and party information.

3. Map Toolbar

The Map Toolbar lets you edit the appearance of the map and symbols. All functions are available when Map is selected as the basemap. When the Satellite map is used as the basemap, only Map Opacity and Icon Size are available. You can switch between the Map or Satellite basemaps by selecting the preferred basemap on the top right of the map.

Map Opacity

The Map Opacity control bar allows the map background's transparency level to be adjusted. It is especially useful when the Satellite basemap is on; symbols show up more clearly when the map background is more transparent.

Before: Map Opacity ≈ 15%

After: Map Opacity ≈ 75%

Icon Size

The Icon Size control bar allows you to change the size of all the symbols displayed on the map.

Street Names

When using the Map basemap, you can choose to show/not show the Street Names by checking/unchecking this checkbox.


When using the Map basemap, you can choose to show/not show Landmarks by checking/unchecking this checkbox.


When using the Map basemap, you can choose to show the map in colors or black and white by checking/unchecking the Grayscale checkbox.

4. Tutorial

Task: Create a collision diagram for the area around the intersection of University Avenue and Shattuck Avenue in Berkeley, California. Focus only on head-on and rear-end collisions between cars that were proceeding straight before crashing.

1. Input parameters into SWITRS GIS Map.

In the SWITRS GIS Map tool, query the following customized conditions. (If you have not used the SWITRS GIS Map before, click here for the user guide.)

  • Time Frame: 03-01-2011 to 09-01-2011
  • County: Alameda
  • City: Berkeley
  • Collision Factor: Collision Type = 'Head-On' and 'Rear-End'
  • Party Factor: Movement Preceding Crash = 'Proceeding Straight'
  • Victim Factor: Party Number = '0 to 2'

2. Spatially select the collisions of interest.

In this example, select the 7 collisions around the intersection of University Avenue and Shattuck Avenue. Then, click Create Collision Diagram in the Results box.

3. Fill out map information.

In the Collision Diagram panel's Map Information, type in the following details in the corresponding fields.

  • Primary Street: University Ave
  • Secondary Street: Shattuck Ave
  • Time Period: 03-01-2011 to 09-01-2011
  • Agency Name: SafeTREC

Note the 1 unmapped collision in the Mapping Summary. From here, you can choose to either print this collision diagram as it is or add/edit collisions. The next section covers steps that you can take to further improve your collision diagram.

4. Check for overlapped collisions.

Collisions can overlap if they occur in the same location at different times. To find such clusters, look for areas where there's only one collision symbol surrounded by multiple arrows, pedestrians, or bicycles. After identifying these clusters, follow the next step to adjust their locations.

Note: There are no overlapped collisions in this current example. However, here's how this would look in another example. Compare the number of collision symbols to the mapped collision count (4 vs. 11, respectively). Collisions here are overlapped.

5. Adjust the location of each collision.

To better investigate the environmental factors causing the collisions, relocate collisions to their more accurate and reasonable positions, such as in a specific lane or crosswalk. Without the original collision report, however, the location accuracy will always be somewhat limited.

Example: Collision at intersection of Oxford Street and Berkeley Way

  1. Toggle on Street Names in the Map Toolbar so that you know where the primary and secondary streets of the location are at.
  2. Click on the collision symbol to open up its Collision Details dialogue window. Note that the vehicle was heading north on Oxford St before making a left turn to Berkeley Way. The bicyclist was heading south and proceeding straight.
  3. Switch to the Satellite basemap for striping details and adjust the Map Opacity as needed; this will help you relocate the collision to the appropriate lane
  4. Click on the collision symbol and drag and drop it to its new location.From the Collision Details, we now know that the collision should be moved to left-turning lane on Oxford St.

6. Rotate the collision to fit the direction of the traffic.

In many cases, traffic flow is not completely horizontal or vertical on the map. Collision symbols can be rotated to match the traffic flow direction or the driving lane.

Example: Collision at intersection of University Avenue and Shattuck Avenue

  1. Click on the collision symbol to open up its Collision Details. Verify that the arrow is pointing the correct direction.
  2. Move the collision to the eastbound lane on University Ave. The collision should be slightly left of the intersection since the offset distance and direction is 33 W, as noted in Collision Details.
  3. Adjust the arrow's rotation. Right-click on the collsion symbol and adjust its rotation until the vehicle symbol matches the lane direction and angle.

7. Add an undrawn collision.

  1. Before adding undrawn collisions, first determine which collisions were 'not drawn'. Go back to the SWITRS GIS Map tool and download the collisions data file for the selected collisions.

  2. Compare the CaseIDs in the collisions spreadsheet with the collision information in the diagram to find the undrawn collision. In this example, the undrawn collision is collision #5147031.

  3. Next, go back to SWITRS GIS Map tool and download the parties file; make sure to remove the party and victim factors—you will want all associated parties with the selected collisions, and not just the ones that were 'proceeding straight'.

  4. Collect the required information to add a new collision on the map. Use the codebooks for the collisions and party data files to translate to the following information:

    Crash severity: Injury
    Crash type: Rear end

    Party 1 movement: Proceeding straight Party 2 movement: Parked
    Party 1 direction: Unknown Party 2 direction: East
    Party 1 type: Driver Party 2 type: Parked vehicle

  5. Analyze the collected data. From the above data, you can see that the lack of direction information for Party 1 is why the collision was not drawn in the collision diagram. However, since you now know that the crash type was a rear-end and that the parked vehicle (Party 2) was facing east when it was hit from behind by Party 1, you can judge that the direction for both parties should be the same. Thus, Party 1 direction should also be East.

  6. Add the collision manually. Make sure to account for the collision's offset distance and the offset direction from the intersection. In this example, the collision should be a little right (101 feet East) of the intersection of University Ave and Grant St.

8. Print.

Check the print preview, zoom in or out to include all the collisions you want in the map window, and click Print when you're ready. You can also save it as a PDF by right-clicking (outside of the map) on the page and printing to a PDF printer.
Here is a print preview of the 7 crashes moved and rotated to their more accurate locations and orientations.