Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of travel center operator TravelCenters of America (AMEX: TA) drove off a cliff today, falling as much as 16% in intraday trading.

So what: The stock's drop is in reaction to yesterday's announcement that the company is planning to sell 10 million new shares to fund capital improvements and expansion. If that sounds like a lot of shares, it is. As of the company's most recent quarterly report, it had 18 million shares outstanding, so the addition of 10 million is very significant.

Now what: The company has yet to price or close the transaction, so it's possible that it may sell fewer shares, but it's also possible that it sells the entire amount (there's also a 1.5 million overallotment option for the underwriters) and does so at a level below the current market price. With the stock currently trading well below the company's per-share book value, this seems like it could be seriously dilutive for shareholders. Investors better hope that management has some really great ideas lined up for the new capital or this could seriously hurt the value of their investment.

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.