1. Bus Services: Reducing Costs;Armstrong-Wright et al.,1987
2. Dhingra, C. 2011. Measuring Public Transport Performances: Lessons for Developing Cities, Sustainable Urban Transport Technical Report #9. Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ), Germany.
3. Eboli, L., Mazzulla, G. 2011. Performance Indicators for an Objective Measure of Public Transport Service Quality. European Transport, Transporti Europei (2011) Issue 51, paper No 3, ISSN 1825-3997.
4. EN 13816:2002. Transportation - Logistics and Services - Public Passenger Transport - Service Quality Definition, Targeting and Measurement. European Committee for Standardization.
5. FGSV, 2001a. HBS – Handbuch für die Bemessung von Straßenverkehrsanlagen. FGSV-Nr. 299. Köln.