The following is a partial review of leading studies which demonstrate the impact that roads and motorized use have on elk.

James W. Unsworth, Lonn Kuck, Edward O. Garton and Bart R. Butterfield. 1998. Elk Habitat Selection on the Clearwater National Forest, Idaho.The Journal of Wildlife Management. Vol. 62, No. 4 (Oct., 1998), pp. 1255-1263

Abstract: Habitat management for bull and cow elk (Cervus elaphus nelsoni) may require different forest management standards because of likely sexual differences in distribution and habitat selection patterns. Current standards are based on the habitat use patterns of cow elk. Thus, we located 121 radiocollared elk (101 bulls, 20 cows) 4,527 times in the forested habitats of northcentral Idaho during 1986-90 to determine patterns of habitat selection. During winter, habitat selection patterns of ≥2-year-old and yearling bull elk were similar, but cow elk used more shrub habitats and less-open timber types. Cows typically used moderately steep areas on south-facing to west-facing aspects on the middle to lower elevational portions of the winter range. Bulls were more often found using small benches or ridgetop areas near the upper portion of hillsides. From spring through fall, elk shifted from using a high proportion of shrub and open timber habitats to use of timber habitats. In general, elk in areas with roads used habitats with greater canopy cover. This pattern was most pronounced for cow and ≥2-year-old bull elk. Yearling bulls tended to select habitats in proportion to availability, whereas cow and ≥2-year-old bull elk showed preference for open timber habitats during fall in non-roaded habitats and for timber habitat in areas with roads during summer and fall. Bulls tended to use higher proportions of lower slopes and stream bottoms than did cows during summer, and somewhat steeper areas during fall. Concern over forage production on summer range should be secondary to reducing disturbance and providing secure habitat during fall hunting seasons.

Cole, E. K., Pope, M. D. & R. G. Anthony. 2004. Influence of road management on diurnal habitat use of Roosevelt elk. Northwest Science. Vol. 78 pp 313-321.

Abstract: Road closures are commonly used management tools for Rocky Mountain elk, but few studies have evaluated the effects of limited vehicle access on movement and habitat associations of Roosevelt elk. We examined the influence of road management areas (RMAs) on habitat use of Roosevelt elk in the southern Oregon Coast Range by limiting vehicle access to 35% of the study area. We studied female Roosevelt elk prior to (pre-treatment phase) and during limited vehicle access (RMA phase) from 1991 to 1994. Elk use of open, foraging habitats increased significantly during the RMA phase compared to the pre-treatment phase, but elk used areas <150 m from roads less than expected regardless of vehicle access. In general, elk used areas near roads and areas >300 m from streams less than expected. Conversely, elk used areas near streams, areas >150 m from roads, and recent clearcuts more than expected. Roadless riparian areas should be given management priority for Roosevelt elk. Our data suggested that reduced vehicle access increased use of open, foraging habitats because of reduce human disturbance. Limiting vehicular access should be considered for other Roosevelt elk populations, particularly to lessen impacts of human-related activities during biologically important periods.

Mary M. Rowland1, Michael J. Wisdom, Bruce K. Johnson, and Mark A. Penninger. Effects of Roads on Elk: Implications for Management in Forested Ecosystems.

Abstract: Effects of roads on elk can be divided into two broad categories: indirect effects on habitats occupied by elk, and direct effects on individual elk and their populations. Effects of roads in forested ecosystems in general have been well summarized (Gucinski et al. 2001, Gaines et al. 2003). With regard to elk habitat, the primary effect of roads may be habitat fragmentation; heavily roaded areas may contain few patches of forest cover large enough to function effectively as habitat for elk, especially where elk are hunted (Leege 1984, Rowland et al. 2000). The total loss of elk habitat from road construction is unknown; a rough estimate of 5 acres per linear mile (1.4 ha/km) of road is often applied (Forman et al. 2003). Across the United States, the area occupied by public roads and associated corridors is estimated to be 27 million acres (10.9 million ha); these numbers do not include private roads or “unofficial” roads on public lands (Forman et al. 2003). Roads may also exert more subtle influences on habitat, for example by facilitating the spread of exotic vegetation (Gelbard and Belnap 2003) which may subsequently reduce quality and abundance of forage available to elk. Gaines et al. (2003) listed five road-associated factors in relation to elk: hunting, poaching, collisions, displacement or avoidance, and disturbance at a specific site.

The direct impacts of roads and associated traffic on elk, in addition to outright mortality from collisions with motorized vehicles, can be summarized as follows:

1. Elk avoid areas near open roads. A plethora of studies have demonstrated an increasing frequency of elk occurrence or indices of elk use, such as pellet groups, at greater distances from open roads (defined here as any road where motorized vehicles are allowed). This response varies in relation to traffic rates (Wisdom 1998, Johnson et al. 2000, Ager et al. 2003), the extent of forest canopy cover adjacent to roads (Perry and Overly 1977, Lyon 1979, Wisdom 1998, Wisdom et al. 2004b), topography (Perry and Overly 1977, Edge and Marcum 1991), and type of road (e.g., improved versus primitive; Perry and Overly 1977, Lyon 1979, Witmer and deCalesta 1985, Marcum and Edge 1991, Rowland et al. 2000, Lyon and Christensen 2002, Benkobi et al. 2004), which also correlates with traffic rates. Responses may also differ between sexes, with bull elk demonstrating a stronger avoidance of areas close to roads than do cow elk (Marcum and Edge 1991). Shifts in distribution of elk away from roads may occur across a range of temporal and spatial scales. For example, elk at Starkey were generally farther from open roads during daytime, but moved closer to roads during nighttime (Wisdom 1998, Ager et al. 2003). This pattern was also observed in South Dakota (Millspaugh 1999). In addition, both daily movements and size of home ranges of elk may decrease when open road density decreases. These reductions could lead to energetic benefits that translate into increased fat reserves or productivity (Cole et al. 1997). On a larger scale, entire ranges can be abandoned if disturbance from traffic on roads and the associated habitat loss and fragmentation exceed some threshold level. The ultimate effect of displacement of elk, by motorized traffic as well as other disturbances, is a temporary or permanent reduction in effective habitat for elk. Concomitant with loss of effective habitat are reduced local and regional populations (Forman et al. 2003).
2. Elk vulnerability to mortality from hunter harvest, both legal and illegal, increases as open road density increases. Many factors affect elk vulnerability to hunter harvest, but the evidence is compelling that survival rates of elk are reduced in areas with higher road density (Leege 1984, Leptich and Zager 1991, Unsworth et al. 1993, Gratson and Whitman 2000a, Weber et al. 2000, Hayes et al. 2002, McCorquodale et al. 2003). Closing roads offers more security to elk and may decrease hunter densities (fewer hunters may be willing to hunt without vehicle access). Also, poaching losses may decrease when roads are closed (Cole et al. 1997).
3. In areas of higher road density, elk exhibit higher levels of stress and increased movement rates. Higher levels of physiological indicators of stress, such as fecal glucocorticoids, have been observed in elk exposed to increased road density and traffic on roads (Millspaugh et al. 2001). In addition, the energetic costs of moving away from disturbance associated with roads may be substantial (Cole et al. 1997). Research to estimate such costs to elk in relation to recreational use on roads is underway at Starkey (Wisdom et al. 2004a). Conversely, elk may conserve energy by traveling on closed roads to avoid woody debris and downfall (Lyon and Christensen 2002).

Montgomery, R. A., Roloff, G. J. and Millspaugh, J. J. (2013), Variation in elk response to roads by season, sex, and road type. The Journal of Wildlife Management, 77: 313–325.

Abstract: Despite the near universal recognition that roads negatively affect wildlife, the mechanisms that elicit animal responses to roads are often ambiguous or poorly understood. We conducted a multi-year, multi-season study to assess the relative influence of roads on elk (Cervus elaphus) in a human-dominated landscape in South Dakota. We evaluated the effects of habitat covariates including security cover, forage quality, distance to roads (primary, secondary, and tertiary), and visibility from roads at the home range scale. We radio-collared 28 elk (21 adult females and 7 adult males) and calculated seasonal (winter, spring, summer, and autumn) utilization distributions (UDs). We assigned habitat covariates to use percentiles within the UDs (1% increments; from 1 to 98 percentiles) and used spatially explicit mixed linear regression to model the relationship between use percentile and habitat covariates. For each season and sex, we evaluated 15 candidate models and used Akaike's Information Criterion weights (ω_i) to identify top-ranking models. We plotted influential coefficients from these models with 95% confidence intervals to examine the magnitude of effects. Our analysis revealed fundamental differences in response to roads, by road type, between sexes, and across seasons. Male elk established home ranges near roads devoid of vehicle traffic in winter, spring, and autumn. In summer, coinciding with peak vehicle traffic levels, male elk reduced their use of habitat that was both visible from and close to primary roads. Female elk subherds similarly responded to primary roads in spring and autumn, during times of year when they were calving and mating, respectively. In spring and summer, female elk subherds selected habitat near roads that were closed to vehicle traffic. Forage quality and security cover were influential in the periphery (>50th use percentile) of elk home ranges, whereas road covariates were more influential towards the core of elk home ranges. This analysis further demonstrates the utility of visibility from road metrics and suggests that the retention of vegetation structures that screen visibility potential from roads could be important components of elk management strategies.

Trombulak, S. C. and Frissell, C. A. (2000), Review of Ecological Effects of Roads on Terrestrial and Aquatic Communities. Conservation Biology, 14:18–30.

Abstract: Roads are a widespread and increasing feature of most landscapes. We reviewed the scientific literature on the ecological effects of roads and found support for the general conclusion that they are associated with negative effects on biotic integrity in both terrestrial and aquatic ecosystems. Roads of all kinds have seven general effects: mortality from road construction, mortality from collision with vehicles, modification of animal behavior, alteration of the physical environment, alteration of the chemical environment, spread of exotics, and increased use of areas by humans. Road construction kills sessile and slow-moving organisms, injures organisms adjacent to a road, and alters physical conditions beneath a road. Vehicle collisions affect the demography of many species, both vertebrates and invertebrates; mitigation measures to reduce roadkill have been only partly successful. Roads alter animal behavior by causing changes in home ranges, movement, reproductive success, escape response, and physiological state. Roads change soil density, temperature, soil water content, light levels, dust, surface waters, patterns of runoff, and sedimentation, as well as adding heavy metals (especially lead), salts, organic molecules, ozone, and nutrients to roadside environments. Roads promote the dispersal of exotic species by altering habitats, stressing native species, and providing movement corridors. Roads also promote increased hunting, fishing, passive harassment of animals, and landscape modifications. Not all species and ecosystems are equally affected by roads, but overall the presence of roads is highly correlated with changes in species composition, population sizes, and hydrologic and geomorphic processes that shape aquatic and riparian systems. More experimental research is needed to complement post-hoc correlative studies. Our review underscores the importance to conservation of avoiding construction of new roads in roadless or sparsely roaded areas and of removal or restoration of existing roads to benefit both terrestrial and aquatic biota.

Gregory R. Rost, G. R. and J. A. Bailey. 1979. Distribution of Mule Deer and Elk in Relation to Roads. The Journal of Wildlife Management. Vol. 43, No. 3 (Jul., 1979), pp. 634-641

Abstract: Responses of deer (Odocoileus hemionus) and elk (Cervus canadensis) to roads were assessed by counting fecal-pellet groups near roads on winter ranges. Data were obtained in Colorado in shrub and pine habitats adjacent to paved, gravel, and dirt roads east of the continental divide; and in shrub and juniper woodland habitats west of the divide. Deer and elk avoid roads, particularly areas within 200 m of a road. Road avoidance was greater (1) east, rather than west, of the continental divide, (2) along more heavily traveled roads, (3) by deer, when compared to elk, and (4) for deer in shrub habitats when compared to pine and juniper habitats. Because of less snow accumulation, winter habitat is more available to cervids east of the continental divide where more pronounced avoidance of roads presumably results from a greater availability of habitat away from roads.

Lyon, L. Jack. 1979. Habitat Effectiveness for Elk as Influenced by Roads and Cover. J. of Forestry. Volume 77, Number 10, 1 October 1979 , pp. 658-660(3)

Abstract: Pellet counts conducted over an eight-year period confirmed that elk in western Montana tend to avoid habitat adjacent to open forest roads. The area avoided increases where the density of tree cover is low. Forest roads open to traffic cause available habitat to be less than fully effective. A method for determining the losses of effective habitat is presented.