If you are an employee in the DC area you can expect to be reimbursed for your business related travel expenses. If using your personal vehicle for travel you will receive a mileage reimbursement rate. The rate is consistent with the IRS rate, which is currently set at $.445 per mile. Keep in mind that this rate is the maximum amount allowed as a tax deduction.
Some employers will give you a travel allowance before you set out. You may be given a company credit card or travel vouchers to be used. Others will set a per diem amount at which you will be reimbursed for all expenses. Most will require your travel to be pre-approved; however that is up to the individual employer.
When it is necessary for you to travel for work you are expected to use the most cost effective method of travel. All reasonable methods of travel should be considered.This includes airline, train, bus, rental car, or personal vehicle. If for instance you are traveling a far distance, you may not want to use your own vehicle. It is important to check with your employer how they want your expenses to be itemized and for which they require receipts.
While high gas prices today are a major concern, there are other factors that should be considered. Additional costs associated with driving include toll charges, ferry fees, bridge road and tunnel fees, and parking charges. Time may be a consideration also.
If you work for a company that requires a lot of travel than they will probably have set standards as part of their company policy. If travel is not a usual part of your duty than you should discuss with your employer what they will compensate you for, how to get reimbursement and how long it will take.