Travel Center

Avalanche Information Q & A's

Avalanche Management on the State Highway System, An Informational Q & A

Q.  What are avalanches and what causes them?

A. Avalanches are masses of snow sliding down slopes. According to the Colorado Avalanche Information Center (CAIC), there are several types, but the most dangerous are slab avalanches. Slab avalanches can form when stronger snow overlies weaker snow. Often, human triggered slab avalanches are one to two feet deep, have an area about half the size of a football field, and can reach speeds over 20 mph within seconds. The other problematic avalanche type in Colorado is a loose snow avalanche. Loose snow avalanches happen when the surface snow has little strength; they tend to occur more often in the spring, when the snowpack surface is rapidly warming and losing strength. They usually start from a point under trees or cliffs. A chunk of snow starts tumbling, knocking more snow loose. The loose avalanches fan out as they descend.

Q.  What does the Colorado Department of Transportation do to protect drivers from avalanches impacting state highways?

A. To help predict avalanche conditions and the necessity for avalanche control, the Colorado Department of Transportation (CDOT) teams up with the CAIC, whose forecasters monitor current weather conditions, weather forecasts, snow depth and characteristics, wind patterns and more. Some factors that increase the risk of avalanche danger are large quantities of new snow, high winds and drastic changes in temperatures.  When there is a high risk of avalanche danger as determine by the CAIC, CDOT will close highways at the location of the avalanche path in order to conduct avalanche mitigation.* Once all the unstable snow has been brought down, CDOT crews work to clear all of the snow and debris from the roadway before reopening the highway to traffic. This clearing can be quite time-consuming, depending upon how much snow was brought down, how many highway lanes are affected and weather conditions. At times the highway may be closed for a period of hours. When avalanche danger is too high and weather conditions (including visibility) prevent CDOT and CAIC crews from conducting avalanche control, the highway could be closed indefinitely while conditions persist.

*CDOT/CAIC avalanche teams can use the following to trigger slides (please note, however, not all these measures are used on every slide path):  5-pound charges set by hand; a truck-mounted “avalauncher” that uses pneumatic pressure to fire 2.2-pound rounds; a 105 Howitzer leased from the Army that can fire 40-pound missiles up to seven miles; a helicopter that drops 30- to 50-pound bombs. (CDOT doesn’t own the helicopter.)


Q.  What does CDOT’s avalanche program involve?

A. The Colorado Department of Transportation’s Avalanche Atlas has more than 522 known avalanche paths. Since 1992 CDOT has been partnering with the CAIC to regularly monitor and/or control more than 278 of those. During the 2013-2014 winter, CDOT experienced 616 hours of road closures due to avalanche control, resulting in a total of 29,866 feet of snow covering the centerline of the roadway. Crews triggered 283 avalanches with explosives, handled 158 natural occurrences and spent 8,908 hours on mitigation.


Q.  How many avalanche fatalities occur in Colorado each year? 

A.  On average, avalanches kill six people in Colorado each year. On Colorado state highways, however, there have been a total of 16 fatalities caused by avalanche slides. Six of these were on US 550 over Red Mountain Pass (three were CDOT plow drivers) and all occurred before 1992, when CDOT and CAIC began avalanche mitigation.


Q.  How many avalanche fatalities occur across the US each year? 

A.  Over the last 10 winters in the US, an average of 28 people died in avalanches every year, according to the CAIC. The CAIC states that every fatal accident is investigated and reported, so these numbers can be recorded with some certainty. However, there is no way to determine the number of people caught or buried in avalanches each year because non-fatal avalanche incidents are increasingly under-reported. Please find charts and data on fatalities and incidents on CAIC’s web page at: (Be sure to cite the CAIC as the source, if used).


Q.  Where are the avalanche paths on the state highway system? 

A.  Here’s a look, by CDOT Region, at the avalanche corridors on the state highway system, and the approximate number of slide paths that CDOT and CAIC crews monitor and/or control on each (please note, these numbers reflect the total number of paths that have the potential to impact the highway; most of these are monitored or controlled on a regular basis, but others only become “active” during exceptionally large snow events or during heavy winters.

REGION 1 (Central Mountains)

US 6 Loveland Pass: 24

US 40 Berthoud Pass: 25

I-70 Georgetown to Frisco: 28

I-70 Ten Mile Canyon: 25

I-70 Vail Pass: 2 (also maintained by CDOT Region 3 crews)

REGION 2 (Southeast)


REGION 3 (Northwest)

SH 65 Grand Mesa:  3

I-70 Vail Pass: 2 (also maintained by CDOT’s Region 3)

SH 82 Independence Pass:  60

SH 133 Crystal River and McClure Pass:  22

SH 139 Douglas Pass:  8

US 24 Battle Mountain (between Red Cliff and Minturn): 11

SH 91: Fremont Pass:  13

REGION 4 (Northeast)

SH 14 Cameron Pass:  10

REGION 5 (Southwest & South-Central)

SH 17 Cumbres & La Manga Passes:  15

US 50 Monarch Pass:  19

SH 145 Lizard Head Pass:  48

US 160 Wolf Creek Pass:   61

US 285 Poncha Pass:  2

US 550 Coal Bank Pass:   20

US 550 Molas Pass:  50

US 550 Red Mountain Pass:  137

REGION 6 (Denver Metro)


Q.  What are Colorado’s highest mountain passes maintained by CDOT? 

A.  The seven highest passes that CDOT crews keep open during the winter are (in feet above sea level):

US 6 Loveland Pass – 11,992 feet

SH 9 Hoosier Pass – 11,541feet

SH 149 Slumgullion Pass – 11,361 feet

SH 91 Fremont Pass – 11,318 feet

US 40 Berthoud Pass – 11,315 feet

US 50 Monarch Pass – 11,312 feet

US 550 Red Mountain Pass – 11,018 feet (This pass has the most avalanche slide paths with the potential to hit the highway in North America.)

Two higher paved state highway passes that are NOT kept open for travel in the winter are: Trail Ridge Road (SH 34) through Rocky Mountain National Park at 12,183 feet, and Independence Pass (SH 82) at 12,095. Both generally close in October or November, depending upon weather, and open just prior to Memorial Day weekend. 

The highest paved road in North America – the Mount Evans Highway on SH 5 – is also closed for the winter and usually opens to traffic on Memorial Day weekend.  This road is not a mountain pass; rather, it’s a road that goes to the mountain’s summit.


Q.  How can I find out when CDOT is conducting avalanche control work?

A.  CDOT will typically post temporary road closure information on its traveler information web site early the morning of the control work, since changing weather conditions and visibility can alter plans. Duration of control work and subsequent highway clearing and reopening will vary, for reasons described above. Crews make every effort to work quickly, but will not reopen a highway until it is safe to do so. Please always check road conditions and road alerts before any winter travel at


Q.  How can media get more information on CDOT’s avalanche control program? 

A.  Please contact the CDOT regional public relations manager in your area at:

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Colorado: The Official State Web Portal