1. EU Thermie Project Sagittaire, Newsletter 2, September 1998.
2. Joseph Beretta, New classification of electric-thermal hybrid vehicles, EVS-15 Symposium, Brussels, 1998.
3. European project APAS-TAUT-0007, Development of a natural gas-electric hybrid city bus with extra low emissions, ALTRA-TNO-CITELEC, 1997.
4. D.A.J. Rand, R. Woods, R.M. Dell, Batteries for Electric Vehicles, Research Studies Press, 1998.