Can Euro V heavy-duty diesel engines, diesel hybrid and alternative fuel technologies mitigate NOX emissions? New evidence from on-road tests of buses in China

•Euro V diesel buses reduce NOX emissions over Euro IV but exceed the limit by 180%.•Diesel hybrid and NG buses are better options to control NOX than Euro V diesel buses.•LNG engines plus SCR provide superior NOX control due to higher exhaust temperature.•Diesel hybrid is the only technology not significantly sensitive to average speed.•Air conditioning reduced NOX emissions of hybrid buses although increased fuel use.