Primary Purpose test: 162 provides that on trips in which the taxpayer engages in both business and personal activities, transportation cost to and from the destination will be deductible only if the primary purpose of the trip is business.
a.    the primary purpose of the trip is to be determined by 1.162-2(b)(1);
i.    In some ways, a 50% rule.  But time is not determinative.  We’re ultimately looking at facts and circumstances to assess the pleasure-to-pain ratio.
b.    if the primary purpose of the trip is pleasure, no transportation cost will be allowed even if business is conducted in some capacity,
c.    Even if you blow the primary purpose test, a deduction may be allowed for travel expenses other than transportation costs (such as food (subject to 274(n)) and lodging) on days devoted to business; (1.162-2(b)(1)).