I need a term or a single word in traditional English or modern English which specifies "a car which has nothing but the driver & empty seats" Please help.
I understand that you are making an observation about vehicles that are being driven and occupied by one person, and hoping to encourage more people to share rides, and thereby reduce overall traffic.
Interestingly,most of the existing terminology used in these situations actually relates to the driver, rather than the vehicle. This makes sense if you consider that the cause of the problem is not the vehicle, but in fact the problem is the driver and their choice to travel alone. Campaigns to improve the sharing of vehicles mostly direct attention to the driver behaviour. Common expressions in this case would include:
'solo-', 'sole-', and 'single-drivers',
'solo-', 'sole-', and 'single-commuters', and
'solo-', 'sole-', and 'single-rollers'.
There are expressions that relate to the vehicles, however, such as:
'Sole Occupant Vehicles (SOV)',
'Sole Occupancy Vehicles (SOV)',
'Single Occupant Vehicle (SOV)', and
'Single Occupancy Vehicle (SOV)'.
Using a term such as 'Single Occupant Vehicle', and its acronym 'SOV' creates as less emotive impression, and is particularly favoured in discussions about road design, including reducing access to 'Single Occupant Vehicles', or the creation of special access for 'High Occupancy Vehicles (HOV)'. See this report for example, from the University of Virginia: http://www.mautc.psu.edu/docs/UVA-2008-04.pdf.
You might note in the previous paragraph a mention of 'High Occupancy Vehicles (HOV)' which is the opposite of a 'Single Occupancy Vehicle'. There are also terms which describe the opposite of a 'Sole Commuter', such as:
'Car Sharer', and
Which also suggests such terms as: 'Ride Sharing', 'Car Pooling', 'Car Sharing' and 'Lift Sharing'. If you were considering a campaign to try to reduce traffic by reducing the number of 'Single Occupant Vehicles' or 'Solo Commuters' you could consider a campaign that was focussed on encouraging the opposite, such as:
'xyz town loves Ride Sharers',
'xyz town loves Car Pooling', or
'Ride Sharers are welcome in xyz town.'.
Most campaigns to encourage ride-sharing also include incentives in terms of reduced road tolls, parking fees, or preferential access onto high speed or high flow traffic lanes. Vehicles using these facilities are monitored - usually by camera - to ensure that Single Occupant Vehicles are excluded. This has led to instances where drivers have placed 'dummies' in their vehicles in order to create the impression that they are carrying real passengers, see: http://www.dailymail.co.uk/news/article-2593704/Worlds-laziest-HOV-lane-dummy-just-hat-t-shirt-seat.html