Deductions & credits

there is no IRS standard commuting mileage. commuting mileage is the actual number of miles you commute.  to determine what is or isn't commuting mileage you must determine what your tax home is.  the following comes from IRS PUb 463.

Tax Home
To determine whether you are traveling away from home, you must first determine the location of your tax home.
Generally, your tax home is your regular place of business or post of duty, regardless of where you maintain your family home. It includes the entire city or general area in which your business or work is located.
If you have more than one regular place of business, your tax home is your main place of business. 
If you don’t have a regular or a main place of business because of the nature of your work, then your tax home may be the place where you regularly live. If you don’t have a regular or main place of business or post of duty and there is no place where you regularly live, you are considered an itinerant (a transient) and your tax home is wherever you work. As an itinerant, you can’t claim a travel expense deduction because you are never considered to be traveling away from home.
Main place of business or work. If you have more than one place of work, consider the following when determining which one is your main place of business or work. (not in the PUB but generally agreed that

a qualifying home office is your main place of business and where you earn the majority of your income or perform most of your work tasks - you can have a home office that is not qualifying)

• The total time you ordinarily spend in each place.
• The level of your business activity in each place.
• Whether your income from each place is significant or insignificant.
Example. You live in Cincinnati where you have a seasonal job for 8 months each year and earn $40,000. You work the other 4 months in Miami, also at a seasonal job, and earn $15,000. Cincinnati is your main place of work because you spend most of your time there and earn most of your income there.
No main place of business or work.

You may have a tax home even if you don’t have a regular or main place of work. Your tax home may be the home where you regularly live.
Factors used to determine tax home.

If you don’t have a regular or main place of business or work, use the following three factors to determine where your tax home is.
1. You perform part of your business in the area of your main home and use that home for lodging while doing business in the area.
2. You have living expenses at your main home that you duplicate because your business requires you to be away from that home.
3. You haven’t abandoned the area in which both your historical place of lodging and your claimed main home are located; you have a member or members of your family living at your main home, or you often use that home for lodging.
If you satisfy all three factors, your tax home is the home where you regularly live. If you satisfy only two factors, you may have a tax home depending on all the facts and circumstances. If you satisfy only one factor, you are an itinerant; your tax home is wherever you work and you can’t deduct travel expenses.
Example 1. You are single and live in Bos-ton in an apartment you rent. You have worked for your employer in Boston for a number of years. Your employer enrolls you in a 12-month executive training program. You don’t expect to return to work in Boston after you complete your training.
During your training, you don’t do any work in Boston. Instead, you receive classroom and on-the-job training throughout the United States. You keep your apartment in Boston and return to it frequently. You use your apartment to conduct your personal business. You also keep up your community contacts in Boston. When you complete your training, you are transferred to Los Angeles.
You don’t satisfy factor (1) because you didn’t work in Boston. You satisfy factor (2) because you had duplicate living expenses. You also satisfy factor (3) because you didn’t abandon your apartment in Boston as your main home, you kept your community contacts, and you frequently returned to live in your apartment. Therefore, you have a tax home in Bos-ton.
Example 2. You are an outside salesperson with a sales territory covering several states. Your employer's main office is in New-ark, but you don’t conduct any business there. Your work assignments are temporary, and you have no way of knowing where your future assignments will be located. You have a room in your married sister's house in Dayton. You stay there for one or two weekends a year, but you do no work in the area. You don’t pay your sister for the use of the room.
You don’t satisfy any of the three factors listed earlier. You are an itinerant and have no tax home.

as to committing mileage vs business mileage again from IRS PUB 463

Transportation
This chapter discusses expenses you can deduct for business transportation when you aren’t traveling away from (tax) home, as defined in chapter 1. These expenses include the cost of transportation by air, rail, bus, taxi, etc., and the cost of driving and maintaining your car. Transportation expenses include the ordinary
and necessary costs of all of the following. 

• Getting from one workplace to another in the course of your business or profession when you are traveling within the city or general area that is your tax home. Tax home is defined in chapter 1.
• 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.
Transportation expenses don’t include expenses you have while traveling away from home
overnight. Those expenses are travel expenses discussed in chapter 1. However, if you use
your car while traveling away from home overnight, use the rules in this chapter to figure your
car expense deduction. See Car Expenses, later (not included - see pUB 437).
Daily transportation expenses you incur while traveling from home to one or more regular places
of business are generally nondeductible commuting expenses. However, there may be
exceptions to this general rule. You can deduct daily transportation expenses incurred going
between your residence and a temporary work station outside the metropolitan area where you
live. Also, daily transportation expenses can be deducted if (1) you have one or more regular
work locations away from your residence; or (2) your residence is your principal place of business
and you incur expenses going between the residence and another work location in the
same trade or business, regardless of whether the work is temporary or permanent and regardless
of the distance.
If you are entitled to a reimbursement from your employer but you don’t claim it, you can’t claim a deduction for the expenses to which that unclaimed reimbursement applies. This type of deduction is considered
a miscellaneous deduction which is no longer allowable due to the suspension of miscellaneous itemized deductions subject to the 2% floor under section 67(a).
Illustration of transportation expenses. Figure B, (PUB 437), illustrates the rules that apply for
deducting transportation expenses when you have a regular or main job away from your
home. You may want to refer to it when deciding whether you can deduct your transportation
expenses.
Temporary work location. If you have one or more regular work locations away from your
home and you commute to a temporary work location in the same trade or business, you can
deduct the expenses of the daily round-trip transportation between your home and the temporary
location, regardless of distance. If your employment at a work location is realistically
expected to last (and does in fact last) for 1 year or less, the employment is temporary
unless there are facts and circumstances that would indicate otherwise. If your employment at a work location is realistically expected to last for more than 1 year or if there is no realistic expectation that the employment
will last for 1 year or less, the employment isn’t temporary, regardless of whether it actually lasts for more than 1 year. If employment at a work location initially is realistically expected to last for 1 year or less,
but at some later date the employment is realistically expected to last more than 1 year, that employment will be treated as temporary  (unless there are facts and circumstances that would indicate otherwise) until your expectation changes. It won’t be treated as temporary after the date you determine it will last more than 1
year. If the temporary work location is beyond the general area of your regular place of work and
you stay overnight, you are traveling away from home. You may have deductible travel expenses,
as discussed in chapter 1.
No regular place of work. If you have no regular place of work but ordinarily work in the metropolitan
area where you live, you can deduct daily transportation costs between home and a temporary work site outside that metropolitan area. Generally, a metropolitan area includes the area within the city limits and the suburbs that are considered part of that metropolitan area. You can’t deduct daily transportation costs
between your home and temporary work sites within your metropolitan area. These are nondeductible
commuting expenses.
Two places of work. If you work at two places in 1 day, whether or not for the same employer,
you can deduct the expense of getting from one workplace to the other. However, if for some
personal reason you don’t go directly from one location to the other, you can’t deduct more
than the amount it would have cost you to go directly from the first location to the second.
Transportation expenses you have in going between home and a part-time job on a day off
from your main job are commuting expenses. You can’t deduct them.

as pointed out if you are an employee there is no federal deduction for business or commuting mileage.  If the company has an accountable plan (you submit mileage reports) and you use your own vehicle then it can reimburse you tax-free using the IRS standard mileage rate for your business mileage. Without such a plan any reimbursement would be considered compensation.  if the state allows a deduction for your business use any reimbursement under an accountable plan would reduce the deductible expenses.   

if you use a company vehicle, they are supposed to include in compensation your personal use (commuting mileage).  usually, the IRS standard mileage rate is used. in addition, it is taxable compensation for both social security and medicare tax purposes.  Nothing prevents the company from including in compensation all use of the vehicle.  if this is the case,  again as an employee, there is no deduction but the business usage could be deductible for the state.