Tax-deductible transportation expenses are the costs of:1
Getting from one workplace to another in the course of your business while traveling in the general area of your Tax Home.
Visiting clients or customers.
Going to a business meeting away from your regular workplace.
Getting from your home to a temporary workplace when you have one or more regular places of work. These temporary workplaces can be either within the area of your Tax Home or outside that area.
Deduct commuting expenses, too. Commuting expenses are nondeductible personal expenses,2 except in one tax-critical instance: if your home office is your Principal Place of Business, you can deduct your costs of getting between your home office and another work location in the same business.3
Transportation expenses do not include expenses you have while traveling away from your Tax Home overnight. Those expenses are Travel Expenses.
For many business owners, the single largest transportation expense is the cost of operating their cars. See Automobile (and Other Business Vehicle) Expenses.
1 IRS Publication 463, “Travel, Entertainment, Gift, and Car Expenses” (2010), page 14.
2 Reg. Section 1.262-1(b)(5).
3 Rev. Rul. 99-7, 1999-5 I.R.B. 4