You're right!

Yes, this reasoning is correct. In general, it is more probable that you will get a number of traffic fatalities that is close to average than one which is far higher than average. This is true whatever the number was for the prior year, since presumably the numbers of traffic fatalities in different years are largely independent. So for this year, it is likely that the number of traffic fatalities will be not too far from average, in which case it will be lower than last year's unusually high value. Statisticians call this phenomenon regression to the mean.