Witsen, V. M., Round Table on Transport Economics, 3., & European Conference of Ministers of Transport. Economic Research Centre. (1978). Scope for the use of certain old-established urban transport techniques: Trams and trolleybuses : report of the thirty-eighth Round Table on Transport Economics held in Paris on 24th-25th March, 1977. Paris : [Washington, D.C.: European Conference of Ministers of Transport.

Witsen, Van M., 38th Round Table on Transport Economics, and European Conference of Ministers of Transport. Economic Research Centre. Scope for the Use of Certain Old-established Urban Transport Techniques: Trams and Trolleybuses : Report of the Thirty-eighth Round Table On Transport Economics Held in Paris On 24th-25th March, 1977. Paris : [Washington, D.C.: European Conference of Ministers of Transport, 1978.

Witsen, Van M., 38th Round Table on Transport Economics, and European Conference of Ministers of Transport. Economic Research Centre. Scope for the Use of Certain Old-established Urban Transport Techniques: Trams and Trolleybuses : Report of the Thirty-eighth Round Table On Transport Economics Held in Paris On 24th-25th March, 1977. Paris : [Washington, D.C.: European Conference of Ministers of Transport, 1978.