Nitrogen oxides, collectively called NOx, from diesel vehicles are considered to be accumulated by particular area of roadsides, so-called "Hot-spot," and result in harmful influence to pedestrians and residents by roadsides. Japanese regulations over emissions of diesel vehicles have been tightened year by year and adopting regulations, emissions in mode test on chassis dynamometer or engine dynamometer have reduced. In this research, it was investigated the effect of introduce of transient mode test, Japanese JE05 mode, to NOx emission in real world and to roadside NOx pollution by road test using on-board measurement system. As test vehicles, 2 ton diesel vehicle which is adopted for Long Term Regulation (steady-state mode test, Diesel 31 mode test, 1998) and 3 ton diesel vehicle adopted for New Long Term Regulation (transient mode test, Japanese JE05 mode, 2005) with on-board measurement system was used. Concerning to road tests of diesel vehicle adopted for Long Term Regulation, NOx and O₂ concentration, intake air flow rate are measured and NOx emission rate and CO₂ emission rates are calculated. Experiments had been conducted from 2000 to 2001 using 17.4 km urban route in Yokohama-shi. Concerning to road tests of diesel vehicle adopted for New Long Term Regulation, NOx and CO₂ concentrations and exhaust gas flow rate sampled by 0.1 second was measured by HORIBA OBS-2200. Experiments had been conducted from 2008 to 2009 on the 22.2 km urban route in Tokyo. And concerning to both vehicles, simultaneously vehicle position by GPS, vehicle dynamics, engine dynamics, driver's operation and road environment were measured. Adopting for transient mode regulation, Japanese JE05 mode, average NOx emission rates became lower by 57.4%, average distance-based NOx emission became lower by 46%. And frequency of spot of distance-based NOx emission was also lower. But concerning to vehicle adopted for New Long Term Regulation, Hot-spots occupied 0.70% of route, this is high compared to 0.19% of vehicle adopted for Long Term Regulation, so that 46% reduction of averaged distance-based NOx emissions are not directly leads to 46% reduction of area of Hot-spots.