CDOT Removing Wildlife Zones Signs, Lowered Nighttime Speed Limits

December 19, 2014 - Statewide Transportation Plan - Motorists urged to slow down, watch for wildlife near roadways this time of year

STATEWIDE - House Bill 10-1238 directed the Colorado Department of Transportation (CDOT) to establish highway Wildife Zones (where there is an increased presence of wildlife near the roadway) with signing for doubled fines for all traffic infractions within the zones. It also gave CDOT direction to reduce nighttime speed limits on up to 100 miles of highways where wildlife crashes are prominent. Driving at reduced speeds at night in wildlife crossing areas is something CDOT and law enforcement agencies have always encouraged. However, the combination of Wildlife Zone and nighttime speed limit signing has not produced statistical data that show this program is effective in reducing speeds and wildlife crashes.

As part of the legislation, sponsored by State Senator Gail Schwartz and former State Representative Kathleen Curry, CDOT was required to prepare a report for submission to the House Committee on Transportation and Senate Committee on Transportation regarding the implementation of the provisions of the bill.

Per the bill, the report contained the following data and information (see link to report, below):

  • the location and length of each wildlife crossing zone that CDOT established;

  • the total number of public highway miles that CDOT established as wildlife crossing zones;

  • the total number and identification of wildlife crossing zones within the state for which CDOT has established a lower speed limit;

  • the effect, if any, that the establishment of each wildlife crossing zone has had in reducing the frequency of traffic accidents within the area of the public highway that has been established as a wildlife crossing zone; and

  • a recommendation by CDOT on whether the General Assembly should discontinue, continue, or expand the establishment of wildlife zones.

LEGISLATION IMPLEMENTATION - During the initial implementation of HB 10-1238, CDOT identified nearly 100 miles of wildlife crossing zones in which reduced nighttime speed enforcement was feasible. The Department did this in cooperation with the Colorado State Patrol and Division of Parks and Wildlife by using several comprehensive data sources to identify the zones’ locations. In each of the zones, the highway was marked with “WILDLIFE CORRIDOR” signs. Nighttime speeds were reduced to 55 miles per hour (mph) only where current speeds are posted at 60 or 65 mph, and only between October 1 through May 1 each year. Where nighttime speeds remained the same, fines were still doubled for speeding (again, only within the Oct. to May timeframe). Along with partners at the Colorado State Patrol, CDOT collected raw data on wildlife hits and enforcement efforts (citations written) in these zones.

The data over the initial study period, which included two full wildlife migration seasons between April 2010 and May 2012, showed a slight decrease in Wildlife-Vehicle Collisions (WVC) overall (among all signed Wildlife Zones) in the two-year period the signs were posted, as compared with the two-year period before signs were posted. Specifically, a 9 percent decrease in WVCs was noted overall.

“There were many variations among these data, however, when we looked at each individual Wildlife Zone,” Region 3 Traffic & Safety Engineer Zane Znamenacek said. “Some saw increased collisions, some decreased; and the decreases were not all during nighttime hours.”

“We did show an increase in our citations written for speeding in Wildlife Zones, as compared with the previous two years,” CSP Captain Rich Duran said. “But we knew we needed to see the results of a CDOT speed study before concluding the overall drop in collisions was a result of a drop in drivers’ speeds.”

CDOT’s wildlife biologist also weighed in on the data review.

“It was unclear if a wildlife population decline may have occurred during the initial two-season study period that could have effected a decline in wildlife collisions,” CDOT biologist Jeff Peterson said. “The decline shown by the data was promising but it could not be substantiated that it was due primarily to the Wildlife Zones pilot. We needed two more seasons to collect data and run speed studies.”

CHANGES IMPLEMENTED AFTER THE FIRST YEARS OF LEGISLATION - Over the past two years, CDOT has supplemented Wildlife Zone collision and citation data with day- and nighttime speed studies on select Wildlife Zone corridors. The series of speed studies was completed to help determine whether there was an actual change in driver behavior.

“Another change we made to the program was extending the enforcement period,” CDOT Region 5 Traffic & Safety Engineer Mike McVaugh said. “After seeing the preliminary data, we determined it would be more beneficial—and credible—to change the enforcement period and signage to October 1 through June 1, instead of May 1.”

NEWEST DATA - CDOT, in coordination with the CSP, compiled the additional two years of data in a report to the legislature in October 2014. The data show wildlife-vehicle collisions and CSP citations before and after the legislation period, as well as the results of speed studies conducted on several signed Wildlife Zone corridors.

The final data (for the full four-season period) show an overall collision decrease of 9 percent in the Wildlife Zones (the same percentage drop as shown in the initial two years of the study). Here are the data highlights:

  1. Wildlife Zones with no nighttime speed reduction, only "fines double for nighttime speeding," showed a reduction of 20%.

  2. Zones with a nighttime speed reduction “fines doubled for nighttime speeding” showed a reduction of 3%.

  3. The best performing study segment showed an average reduction in collisions of 71%--this was on State Highway 13, from 58 to 68.

  4. The worst performing segment showed an increase of 59%--this was on State Highway 9 from 108 to 126.

  5. For the spring season, the overall reduction was 22%.

  6. For the fall season, there was an increase of 3%.

  7. Law enforcement citations increased 43% following implementation of the wildlife zones.

  8. Of the 14 study segments, eight segments exhibited an improvement in wildlife collisions, while six segments exhibited increased collisions.

  9. Nighttime speed limit reductions were ineffective. Based upon the recent two years of speed study data, CDOT found that drivers tended to exceed the nighttime speed limit reduction by an average of 7 mph.

CDOT’s recommendation to the legislature was the following:

While data do show a minor improvement on average in accident history, the fact that six of the 14 segments (43%) exhibited worse accident history following implementation of the wildlife zones indicates this program cannot be expected to reliably reduce wildlife vehicle collisions on any given corridor. Based on the inconclusive data, it is CDOT’s recommendation that the signs be removed. Per the data, changing driver behavior was found to be ineffective with this signing program.

CDOT has been turning down the Wildlife Zone signs along all corridors and the speed limit reduction signs have been turned away, soon to be removed altogether.

“We cannot, per state statute, leave regulatory speed limit signs on the highway that are not supported by data and/or an official speed study,” McVaugh explained. “We do, however, completely support the need for motorists to slow down in wildlife areas at night, especially during the fall the spring period. Slowing down and scanning the roadsides ahead will give drivers that extra time they need to react, and hopefully avoid a collision.”

Wildlife data (including collision data by county) and the 2014 report to the Legislature can be found at

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