KSU has the highest Beta of all the railroads. With a beta of 1.5, over reasonable periods, the shares will move about 50% more than other rails and the markets in general. This applies to the upside, and more recently, to the downside.
There is also the good old fashioned flight to safety aspect of the markets at this point. KSU is not a large cap stock; it is a mid-cap. During periods of higher volatility, mid-cap stocks tend to get sold harder than large caps, due to their lower relative liquidity.