National Park Service has proposed increasing the number of snowmobiles and other snow-machines allowed into Yellowstone National Park, according to FOX News. The agency said new pollution and noise control requirements would curtail environmental effects. The public has 45 days from June 29 to comment on the plan. This would allow a maximum of 480 snowmobiles plus 60 snow coaches per day into Yellowstone. The average number of snowmobiles per day could not exceed 342 over a winter season. Currently, there is a daily limit of 318 snowmobiles and 78 snow coaches in recent years. The park's daily average was 190 snowmobiles and 35 snow coaches. The agency's proposal would also set lower noise and emissions requirements on snowmobiles starting in 2017. The proposal also keeps the eastern entrance open for snowmobilers from Cody. This would require crews to trigger avalanches on Sylvan Pass to allow for safe passage.