We are purchasing our vehicles rather than leasing them this year. Under the lease we were debiting vehicle expense to each individual dept that had a vehicle assigned to them. Now that we are purchasing them - can you still charge vechicle expense or do I have to debit depreciation expense?

You're purchasing an asset and it has to be capitalized. i.e. you're debiting an asset.

If you're asking just about the periodic charging to an expense, it's depreciation and it's done as an adjusting entry. And you have to pick a method to use for it. Do you have an accountant who has been doing your other depreciation? If so, I would call that person, give them the info, and let you know how much to depreciate each month/year. They would want that info anyway.

If you have your expenses divided up by department, you can still create a separate depreciation account for each of the departments.