Pacific Newt Roadkill & Traffic Patterns (2019-2020)
Slow-moving amphibians are particularly vulnerable to road-related mortality. Our team has documented massive Pacific Newt roadkill on Alma Bridge Rd. at Lexington Reservoir, CA since 2017.
In order to devise effective mitigation strategies to help the newts cross the road safely, it's important to understand traffic patterns in this area. We know that certain agencies have been collecting traffic data on Alma Bridge Rd., but we've been unable to obtain their data. So we started collecting our own data in 2019. However, our data are snapshots of mostly 2-hr windows of time during daylight hours two times per week. What we need is 24-hr surveillance 7 days/week over a period of months so that we can correlate newt roadkill with traffic patterns.
Who uses this road?
Residents, hikers, bikers, boaters, equestrians, Santa Clara County (SCC) Parks and Midpen rangers, PG&E, Vulcan Materials Co., San Jose Water Co., Los Gatos Rowing Club, UCSC Puma Project.
What We Know
Traffic is much heavier in the (recreational) northern half of Alma Bridge Rd. during daylight hours. Traffic is lighter in the (residential) southern half of the road.
** Our team documented a total of 1,469 motor vehicles during 55 surveys last year; 882 in the north; 587 in the south.
** 1,223 motor vehicles have been documented during 19 surveys this year; 922 in the north; 426 in the south.- The northern half of Alma Bridge Rd. includes 3 open space trailheads, 2 boat launch sites, the Vulcan Materials quarry road, 4 parking lots, and miles of roadside parking.
- The southern half of Alma Bridge Rd. includes the SCC Water facility and many residences, including those along Soda Spring Rd., as well as miles of roadside parking.
- Alma Bridge Rd. provides both northern & southern access to Highway 17.
- Posted speed limit is 25 mph, 15 mph around curves. However, many motorists exceed the speed limits.
- 8 Newt Crossing signs were installed by County Roads in 2019. However, they were not successful in reducing the newt roadkill.
- [placeholder - need to replace with population data for Lexington] Human populations in Santa Cruz County increased 39% from 1980 to 2010 (U.S. Census Bureau, 1995; U.S. Census Bureau, 2010). Commuters in the overall Santa Cruz County have increased 43% from 1980 to 2000 (SCCRTC, 2000).
Figure 1 shows the total traffic we've documented on Alma Bridge Rd. during our surveys. It shows heavier daytime traffic on the northern half of the road.
What We Suspect
- Traffic has increased significantly at Lexington Reservoir in recent years due to increased use of recreational facilities and residential expansion in the area.
- Total vehicle traffic rates are higher during commute hours. Rush-hour traffic may be responsible for nighttime mortality, at least in the southern section of the road.
- When hundreds of newts are migrating across the road, a single vehicle can have a devastating effect, killing dozens, if not hundreds of newts at a time.
Figure 2 begins to show what we've suspected - traffic has increased significantly over the years.
Confounding Issues
The Covid-19 Pandemic and associated business closures and lockdown orders have altered traffic patterns in the area since March 2020.
** @newtpatrol has noticed a significant increase in traffic in the southern half of our study area on weekdays during 2020 due to COVID-19.
