Deviation of the real driving fuel consumption from the measured fuel economy given in vehicle specifications is a growing concern for certain groups of researchers, motorists and organizations. The motivations of the concern are from caring about the world environmental changes to very individual costs for motorists. The amount of deviation is blamed on vehicle manufacturers, car owners, service technicians and even poor country economies having more inferior roads, fuels and materials available. It is vital to differentiate between the fuel consumption variations caused by different driving conditions, driving styles, vehicle technical condition, fuel quality, car manufacturers increasing expertise of achieving or cheating low consumption test results and other factors. The paper shows vehicle driving energy requirement modeling for urban stop and go traffic at various average driving speeds. The modeling results are compared with real environment driving in the Latvian capital city Riga. Diverse driving conditions are modeled within urban driving speed limits. The car speed - time modeling function is reduced to simple and discrete constant acceleration and coast down events. The computer modeling and road test results show considerable variation of traction energy depending on the driving pattern. The paper forms an essential section in a more extensive research of fuel consumption in city driving.