My spouse is an independent contractor/consultant working under
contrat with a public entity.  She travels to and from the public
entity about four times a week (approximately 100 miles round trip). 
The travel also involves $6.00 in bridge tolls daily.  Assuming that
she has accurate records, are her travel expenses (mileage and tolls)
deductible as a business expense?

Hi buzzstar,

You haven't provided enough information for a conclusive answer, but I
will explain the rules and leave the application to your spouse's case
to you and her.

Expenses for commuting, defined as travel between home and workplace,
are not deductible, but expenses for travel between two workplaces
are.  Wayne M. Davies says that a self-employed person like your
spouse could deduct all of her transportation expenses by maintaining
a home office and departing from there in the morning and returning to
the home office in the evening, thus converting all the travel outside
the home to travel between two workplaces, so the cost is deductible.

http://www.howtoadvice.com/DeductMileage

It's up to you and your spouse to decide how closely this theory
matches the reality of her work and how far you want to push it.

Whether the workplace is temporary also makes a difference.  In a
Small Business Calendar page, the Internal Revenue Service says, "you
are usually allowed to deduct transportation costs for going from your
home to temporary workplace."

http://www.irs.gov/businesses/small/article/0,,id=105708,00.html

If you are deducting business automobile expenses, you have a choice
of deducting actual operating expenses or mileage at a standard rate. 
If you use the standard mileage rate, you can also deduct tolls as an
additional expense.  This is also on the IRS page linked above.

The standard mileage rate changed during 2005.  It was 40.5 cents per
mile from January through August and 48.5 cents per mile from
September through December.

http://www.irs.gov/newsroom/article/0,,id=147423,00.html

Important disclaimer:  Google Answers does not provide professional tax advice.

I hope this explanation is helpful.  If you need any more information
about this, please ask for a clarification.

--efn

The answer resolved a basic question.  For further advice, I think
that I would need a CPA or a tax lawyer.