Wildlife Underpasses on Indian Highways: What They Are and Who Uses Them

A camera trap set inside a concrete culvert beneath NH-44 in Madhya Pradesh once captured a tiger padding through at 2 a.m., unhurried, following a scent trail that predated the road above it by centuries. The underpass had been there for three years before the tiger showed up. That gap, between when a structure is built and when an animal decides to trust it, is the real story of wildlife underpasses in India.

India's highway expansion has been one of the fastest in the world over the past two decades, with the national highway network more than doubling in length since 2000. This growth has carved through forest corridors that large mammals depend on for breeding, foraging, and seasonal migration. The Western Ghats, the Terai Arc, the Shivalik hills, and the Central Indian tiger landscape all have highways cutting across them. Road mortality, animals killed by vehicles, is documented for tigers, leopards, elephants, sloth bears, pangolins, and dozens of reptile species. But the less visible cost is fragmentation: when a population on one side of a road cannot reach the population on the other, genetic diversity drops over generations. Underpasses were built to address both problems at once.





There is no single design. The National Highways Authority of India and state forest departments have used box culverts as narrow as 1.5 metres wide, concrete pipes barely large enough for a jungle cat, and wide underpasses spanning 20 metres or more with earthen floors and open sides to let in natural light. Width matters enormously. A 2-metre culvert will be used by small carnivores, porcupines, hares, and reptiles. An elephant needs a passage at least 8 metres wide and tall enough to walk without lowering its head, roughly 5 metres clearance. The most studied underpasses in India are along NH-212 and NH-766 through Nagarhole and Bandipur in Karnataka, where the highway bisects one of the highest-density tiger habitats in the world. These were retrofitted with wider passages and earthen ramps after camera trap data showed animals approaching the road edge and turning back. Vegetation planted at the entrance, matching the forest floor on either side, reduced that hesitation significantly.


Camera trap grids placed at underpass entrances and exits have produced some of the most detailed wildlife crossing data collected anywhere in Asia. In the Nilgiris Biosphere Reserve, surveys have recorded Asian elephants, gaurs, sambar deer, leopards, dholes, striped hyenas, Indian civets, porcupines, monitor lizards, and king cobras all using underpasses within the same study area, though not the same passage. Elephants and gaurs use the widest structures almost exclusively. Leopards and dholes use medium-width passages but avoid them when human activity, vehicles, noise, torch light, is detectable nearby. Small mammals and reptiles use even the narrowest culverts, often at far higher frequencies than large species, but they attract less attention in reporting. One finding from Bandipur that surprised researchers: tigers used underpasses more readily than leopards, possibly because tigers in that landscape are less averse to open ground and have larger home ranges that make crossing worth the risk.



Not every structure works. The reasons are specific and documented. Passages that open onto a cleared buffer, mowed grass, bare soil, no shrub cover, are avoided by most species because they offer no concealment on exit. Underpasses near toll plazas, truck rest stops, or villages with high human foot traffic show near-zero large mammal use even when the structure itself is well-designed. Water accumulation inside concrete culverts during monsoon makes them impassable for months and breaks the habit of use that animals build up over dry season. Some passages were built at locations chosen for engineering convenience rather than animal movement data, they sit between two forest patches that animals were not actually moving between. The Wildlife Institute of India has flagged this repeatedly: underpass placement needs to follow GPS collar data and kill-site mapping, not just the nearest forest boundary on a map.

The structure is the beginning, not the solution. Camera trap monitoring after installation is what determines whether a passage is functioning, and that monitoring has been inconsistent across projects. Where it has happened, Bandipur, Pench, Corbett, and parts of the Terai Arc, it has led to practical adjustments: planting native ground cover at entrances, installing water drainage, reducing lighting near passages, and in some cases physically blocking informal cattle tracks that were drawing domestic animals through and deterring wild ones. The Pench Tiger Reserve corridor has documented breeding tigers on both sides of NH-7 using the same underpasses, which is the clearest evidence that the passages are doing what they were designed to do, not just allowing individual animals to cross, but keeping populations connected enough to find mates.