Complex sentence: In 1906, the electric tram line was opened for service between Frascati, Rome and Castelli Romani, they traveled wholly along tracks laid down in streets as interurban electric streetcar (light rail).
Split into simpler sentences: In 1906, an electric tram line opened for service between Frascati, Rome and Castelli Romani. The trams traveled wholly along tracks laid down in existing streets as an interurban electric streetcar (light rail).