Economic driving or energy-efficient driving plays a crucial role at reducing pollution caused by mass-production cars and fuel consumption. Operating a technical system at its most efficient set point is well known. But economic driving in traffic scenarios are more difficult to traffic flow, road grades and engine characteristics. In this study, the scalar energy-efficient variable is defined in order to seek energy efficient set point of the engine dynamics producing driving torque as a response to the travelling tasks in the road infrastructure and traffic. As an alternative solution to the well presented nonlinear controllers, a rough modelling is used to enable mobile computing on a smart-phone as an on-board unit in the car measuring the vehicle controller area network, global positioning coordinate system information and acceleration information. Overall, from the nonlinear controller design including its stability proof to the human-machine interface design to be used in road tests is elaborated. A 11% energy saving is obtained during road tests by using the presented on-line mobile and portable solution. Copyright (C) 2021 The Authors.