Accident Studies: Deer-vehicle collisions

Data from CT DEP and DOT

Correction factors for roadkills and auto accident numbers

A study by Connecticut Department of Environmental Protection (DEP) in 2003 demonstrated that for every dead deer found by the road there were 8.6 auto accidents with deer and 5 more deer that were also killed by vehicles but not recorded as dead. This study used data from 8 towns across the state and compared deer roadkill data submitted to DEP with state trooper vehicle accident reports involving deer.
Thus the correction factor for deer roadkills is 6 and the correction factor for deer-vehicle accidents is 8.6. Both correction factors are applied to the number of deer that are killed and reported to DEP. So if 100 deer are reported to DEP, then 860 deer are actually hit by motor vehicles (some may die and some survive).  (Communication from Howard Kilpatrick at CT DEP).

  "Why do there appear to be more deer-vehicle accidents during hunting season?"

           In CT hunting season extends from mid September to the end of January, and only occurs during the day (½ hour before sunrise to sunset) and never on Sundays. Police accident reports show that deer-vehicle road accidents are not equally distributed throughout hunting season but peak when the days are short and peak rush hour or "drive time" overlaps the time of sunset. and the hours immedatley after. Thus most deer-vehicle accidents do not occur during daylight hours when hunters are around. Hunting is not permitted after dusk and therefore hunters cannot be the cause of the increase in these accidents at this time of year.  Rather dawn and dusk are when deer are naturally more active, so the overlap of this deer activity with that of peak traffic will result in more accidents.  In November this peak also coincides with the deer mating season, or rut, when deer are also more active and distracted as they pursue each other.  Deer-vehicle accidents also frequently occur on Sundays, a day on which there is no hunting permitted in Connecticut at any time of day.
The Alliance asked the CT DEP Wildlife Division to conduct a review of the frequency, distribution and timing of deer-vehicle accidents, based on reports received by state and local police departments.  The distribution and timing of vehicular traffic, based on data provided by the Department of Transportation also was examined to investigate this claim.
The following is a summary of this DEP review:

Hunting is allowed on Monday through Saturday, but is prohibited on Sundays.  In short, hunting does not occur after dark or on Sundays. We looked at the timing of deer vehicle accidents relative to day of the week and time of the day.   

If hunting activity contributed to deer-vehicle accidents, we would expect this effect on deer vehicle accidents to be highest on Saturday because most hunting occurs on Saturdays and lowest on Sunday because no hunting is permitted on Sundays.  During the 5-week firearms deer-hunting season in November and December, Friday and Saturday were days with the lowestnumber of deer-vehicle accidents (Figure 1).  More accidents actually occurred on Sundays when no hunting is allowed.  Interestingly, deer-vehicle accidents were relatively high on weekdays and relatively low on weekends.  This pattern was also evident when looking at deer-vehicle accidents by day for the entire year (figure 2).  This closely corresponds with vehicular traffic patterns.  Vehicle traffic volume was higher on weekdays and lower on weekends.  This suggests that traffic volume was a significant factor in deer-vehicle accident rates.
Figure 2.

If hunting activity contributed to deer-vehicle accidents, we also would expect deer-vehicle accidents to be highest during hunting hours (1/2 hr before sunrise to sunset) when hunters are in the woods and lowest at night when hunting is prohibited.  Data on time of day of deer-vehicle accidents in the town of Greenwich does not support this concept.  Deer vehicle accidents actually peak about 1 to 4 hours after dark (see figure 3). 
Figure 3.

 Again, this peak closely corresponds with peak traffic volume at the end of the workday.

No scientific data supports the claim that hunting activity increases the rate of deer-vehicle accidents.  However, the data does support the fact the vehicular traffic patterns influence deer vehicle accidents.  Removing deer through hunting or other deer management techniques is an effective method to reduce deer populations, which will result in fewer deer-vehicle accidents.