Deer and Bunnies and Less-cute Things

Animals aren't good at crossing highways or railways. Highways, with their almost constant traffic, split the natural habitats of a lot of creatures. The easiest to visualize is a highway along a river or stream. Animals need water, so they need to cross the road. They often don't make it.

At the larger scale, a freeway can sever the natural migration of the majority of a species. The same effect is possible with a high speed railway. Luckily, as California's system is built, it will reap the benefits of scholarship about mitigating the severing of migratory species.

On a ride from Fresno to San Luis Obispo a few years back, I was fascinated by the construction along State Route 41, west of Interstate 5, where the 2-lane roadway was being replaced by a 4-lane expressway. In one section, the new highway was about 6 feet higher than the existing road, and there were large box culverts (box-shaped pipes) passing under the new highway grade all long its path. These were there to let smaller wildlife cross the new highway unimpeded.

Following this experience, I became aware of the mitigations for wildlife that can be engineered in to a project. I found it's just not enough to provide the culverts for the creatures, you need to plant some cover at each side of the culvert so the animal just doesn't pop out into the landscape on the other side. Why? Predators will soon learn that the hole under the roadway serves up a tasty selection of snacks. With cover plantings at each side, the prey can hide in vegetation that they're familiar with and survey the path ahead to ensure it's clear of predators before continuing their journey.


This is a bat cave built along a new high speed line in Germany

For larger creatures, larger undercrossings or even a short tunnel to allow the natural habitat to flow over the railway are appropriate. Along the line in England, there are a few locations where short tunnels were placed as an environmental mitigation. The same exists along lines in Germany and I'm sure elsewhere. In England, some of the tunnel sections were built using pre-built concrete arch sections that locked together over the railway to form the tunnel structure. The cut in the landscape surrounding the railway and tunnel arch was then filled back up with the soil originally excavated.

The high speed railway knows it needs to tread lightly in sensitive places. The know-how to do this has been established in locations all over the world. The deer and bunnies need not worry.