Norfolk County Council is testing 30 vehicles. The range includes hybrid-electric, all-electric, liquefied petroleum gas (LPG) and bio-diesel vehicles.
Project manager Stuart Hutchinson said the authority was keen to test the vehicles properly in a practical working situation and across a range of temperatures and weather conditions.
The trial aims to highlight the vehicles' practicality, reliability, driving experience, financial implications, noise levels and the logistics of refuelling.
Those currently being tested include the Honda Civic IMA, Ford Transit, an electric Citroen Berlingo and LPG-powered Astra vans.
Hutchinson highlighted the fact bio-diesel was of particular interest to the Norfolk agricultural community as it can be made from crops such as rapeseed and sugar beet, which are already farmed in East Anglia.
However, the council has to be cautious in its use of bio-diesel in the trials because some manufacturers will not validate vehicle warranties if the fuel is used in a greater mix than 5%.
Hutchinson said: 'The council's aim in conducting the trials is to test alternative fuels in a working situation, so that direct comparisons between different alternative fuels can be made. Ultimately the objective is to increase use of alternative fuels in the county council fleet.
'The trials will enable us to make an informed decision about wider use of alternative fuels in the county council fleet and thereby contribute to an improvement in local air quality. It could well be that the council will decide, after the results of the trials have been analysed, to utilise a number of alternative fuel options and match the best option to the operating conditions and operating environment of particular vehicles.'
All the vehicles will undergo regular emission tests on pollutants such as carbon dioxide, carbon monoxide, hydrocarbons, nitrogen oxides and particulate levels.