Prior to 2018, exchanges were allowed for various asset types. However, beginning in 2018, exchanges are only allowed for real estate assets.
Therefore, you will take your vehicle mileage on the old vehicle through the date you traded it in, and then you will "sell" it. The "sales price" is the amount you traded it in for. The "cost or other basis" is the depreciated value of the vehicle you traded in.
Then you establish your new asset at cost and take mileage on it for the remainder of the year.