Kathryn Harrold

EXECUTIVE SUMMARY
Many California interstates provide commuter traffic and goods movement among regions and cities through wild, protected areas. Collisions between wildlife and vehicles occur frequently, which has prompted Caltrans to seek assistance in assessing the nature, extent, and solutions to potential conflict
between traffic and animals. Wildlife-vehicle collisions can pose a risk to human drivers and wildlife populations and species. Interstate 280 (I-280) has seen fatal and non-fatal (to people) collisions between cars and animals. Because of concern about the rate of collisions along this interstate,
Caltrans and the Transportation Enhancement Program of the USDOT saw fit to fund a study of the causes of collisions and possible solutions. The objectives of the study were to understand how wildlife were currently using available under-crossing structures, how wildlife in general and mule deer
(Odocoileus hemionus) in particular interact with the highway and adjacent habitat, and to develop mitigation for risk reduction. This report describes analysis of wildlife-vehicle conflicts and wildlife movement in association with I-280, as well as scenarios for mitigation of impacts to wildlife and
people from collisions. Three types of wildlife observation data along I-280 were used to characterize wildlife movement:
wildlife-vehicle collisions (WVC), images from wildlife camera traps at highway under-crossings, opportunistic track surveys, and deer movement patterns using GPS-collars. WVC occurrences were from Caltrans’ monitoring of carcass retrieval and disposal by Maintenance crews and opportunistic observations of carcasses by participants in the California Roadkill Observation System (http://wildlifecrossing.net/california). We identified statistically-significant WVC hotspots and calculated rates of collisions with any animal and with deer in particular. There are various costs associated with a collision between a deer and a vehicle. On average, a collision with a deer costs $6,671
(Hujser et al., 2009). This cost is borne by society in terms of medical costs, increased insurance premiums, emergency response, lost productivity, and highway safety activities. Caltrans’ mission includes protecting public safety: “Provide the safest transportation system in the nation for users and
workers”, a goal which presumably includes reducing the rates and costs of collisions to the public. We found that the cost of deer collisions on I-280 each year, between 2005 and 2012, varied from <$1,000 to >$40,000 per mile. To put this number in perspective, it can cost ~$20,000/mile to augment a 5-6 foot chain link fence to make it an 8-foot fence and up to $100,000/mile to construct a new 8-foot fence. There were segments of high costs from deer collisions (>$5,000) throughout the study area.  Certain stretches would pay for themselves in terms of avoided costs from deer collisions in a matter of 3-5 years.
We tracked twenty four female deer using GPS collars (Lotek, Inc.) between December, 2011 and January, 2013. Collared deer often approached and moved back and forth near the interstate and two were hit by vehicles. Only 5 of the 24 collared deer passed back and forth under the highway, all using the same 2 crossing structures, a large vegetated underpass and a minor road under-crossing.
Beginning in October, 2011, camera traps captured still and video images at 9 street underpasses, 1 bicycle over-crossing, 6 culverts, and 6 wildlife trails adjacent to crossing structures. We measured species diversity and the relationship between wildlife passage and human use of structures. There was a
strong negative relationship between the presence of humans hiking, driving, walking dogs, or riding bikes and the use of existing crossing structures by wildlife. In addition, there was very low species diversity observed using crossings at either interstate. Only 9 native mammal species were observed to
use crossing structures, which was not a function of camera sensitivity as they could detect movement of small lizards. During 16 fairly continuous months of photo-monitoring of crossing structures, we observed 1,341 mule deer crossings safely under the right-of-way. Because of the rate of traffic on the surface of interstate, it is likely that most deer attempting to cross would be struck. Passing 1,341 deer in 16 months allowed a cost avoidance of 1,341 deer times $6,671/collision = $8.9 million, or $6.7million/year. This could be considered one value of the structures.
Mitigating WVC consists of where to act and what actions to take to reduce risk to drivers and animals. Managing conflict between vehicles and wildlife along I-280 requires identifying priority areas, fencing to keep deer and other animals from accessing the road surface, construction of new underpasses or enhancement of existing structures, and re-management of existing underpasses to reduce human use. Future research should focus on responses of wildlife to reduced human passage at underpasses, the different management required in developed vs. undeveloped areas, and methods to increase species diversity at crossing structures.
PROJECT PURPOSE
There were two purposes of this project cited in the original application for Transportation Enhancement Program funds. First and foremost is to increase the safety of the commuters who choose to drive this Highway by assessment of the wildlife-vehicle collision problem & then ascertaining how to most efficiently reduce the impacts of wildlife-vehicle-collisions, benefiting both wildlife and public. The second purpose of equal importance is to restore the wildlife movement and habitat connectivity across I-280. The lessons learned, data collected and solutions chosen to restore the wildlife movement and habitat connectivity with this project will be available to guide future projects of similar purpose in California, including along I-280 itself.
The section of I-280 that runs through San Mateo County sees many auto collisions on an annual basis due to deer-crossings alone. Human injury can result when vehicles collide with the deer and other large animals. The mitigation solutions recommended here should result in reduction of wildlife vehicle collisions. This reduction is as important to the safety of the commuters as it is to wildlife movement.
There are a handful of strategies used across America aimed at counteracting road-kill and habitat fragmentation. They range from site-specific projects such as underpasses, vegetated overpasses or the widening of box culverts, to regional models that combine landscape ecology, conservation biology and human safety concerns with long-range  transportation planning.
UC Davis Road Ecology Center, Caltrans, District 4, California Department of Fish & Wildlife
Prepared by Fraser Shilling
With assistance from: Tanya Diamond, Ahiga Snyder, Kathryn Harrold, Iara Lacher, Martha Schauss, David Waetjen, Monica Gan, Robert Young, Clara Laursen, David Casady, Craig Stowers
December 13, 2013