Injury collisions of people walking and biking

This web application is in beta status, version 0.1b6. Send bug reports, feature requests, and comments to [email protected] or Twitter @steve_piercy.


The number in each cluster marker indicates the number of collisions in that area.

1 collision
2-4 collisions
5-9 collisions
10-24 collisions
25-49 collisions
50+ collisions


  • Double-click on a cluster marker to zoom in.
  • Click on a green marker to view the details of a collision.
    • Note the offset value (Distance and Direction) from a given Primary Rd and Secondary Rd intersection to determine the actual location of the collision.

Death and injury counts

  • The total number of collisions geocoded (3,603) are only of those people walking and bicycling.
  • 6 collisions where people were injured while biking or walking could not be geocoded because the SWITRS data provided streets that did not intersect.
  • 52,301 collisions where people were killed or injured while driving are not mapped. A version with this feature may be released in the future.

County Safety Ranking

The California Office of Traffic Safety rates Santa Cruz County as one of the worst of all 58 counties in the state for safety for people who ride bikes. For people who walk, it is slightly less awful.

Click the year in the table to view the source of the rankings and to read about the methodology used to determine the ranking.

Year Bicyclists Bicyclists < 15 Pedestrians Pedestrians < 15 Pedestrians 65+
2 11 12 4 15
1 13 18 14 44
4 12 27 18 42
2 11 14 9 52
1 3 8 22 57
1 12 23 16 47
Average Ranking 1.83 10.33 17.00 13.83 42.83


  • The geocoding of these incidents is approximate.
  • Data from 2014 and later is provisional.


  • This is a volunteer project.
  • This project is public.
  • Blame Steve Piercy. He is solely responsible for the content and presentation of data in this project.
  • Please use this project to influence policies and decision-makers to reduce the excessive number of deaths of, and injuries to, people who walk and bike in Santa Cruz County. Urge local advocacy groups to acknowledge and publicize the severity of this problem. Do not remain silent or claim this data will "scare people away from biking"—that's a grave disservice. More groups and agencies must admit this is a serious problem, and advocate that it is unacceptable.

Additional Resources and Technical Notes

  • Raw data was downloaded directly from the Statewide Integrated Traffic Records System (SWITRS).
  • The latitude and longitude values in SWITRS lack sufficient decimal precision to be of much value, so they are ignored.
  • Geocoding of some SWITRS data (2004-2013) was performed by the Transportation Injury Mapping System (TIMS) from the University of California, Berkeley. TIMS does not publicize its algorithms for geocoding data, and they did not respond to my request for this information. This geocoded data, when available, is used to plot collisions.
  • Geocoding is based on the values of PRIMARY_RD and SECONDARY_RD in SWITRS. These include values such as "LIGHT POLE #220", which is utterly useless for geocoding, so the value of PRIMARY_RD within Santa Cruz County was used.
  • Some roads in SWITRS had typographical errors or were close enough to actual street names, and in such cases the errors were corrected by human intuition then geocoded manually.
  • TIMS provides data and mapping analysis tools and information for traffic safety related research, policy and planning. TIMS was inspirational toward the creation of this project, although I wanted something that did not require an account and was easier to use.
  • Vision Zero is a strategy to eliminate all traffic fatalities and severe injuries, while increasing safe, healthy, equitable mobility for all. First implemented in Sweden in the 1990s, Vision Zero has proved successful across Europe—and now it's gaining momentum in major American cities. The Vision Zero Network is committed to helping communities reach their goal of Vision Zero in the United States.
  • The Community Traffic Safety Coalition of Santa Cruz County publishes annual reports on safety for people who walk and ride bikes.
  • Geocoding of intersections was performed using Google Maps API.
  • Additional user interface features include Marker Clusterer and OverlappingMarkerSpiderfier.