The STEEM project is a research and experimentation project in public transport. Its goal is twofold: increase tramway systems energy efficiency and allow a vehicle to run without overhead contact lines. It associates a tram manufacturer (Alstom), a public transport operator (RATP) and a public research laboratory (INRETS) with the financial support of the French governmental agency ADEME under a PREDIT program. It is based on the use of onboard supercapacitors, and a demonstrator has been installed on an existing tramway of RATP T3 line. This vehicle is running in revenue service since late 2009 and delivers its first promising results.