Vehicle emissions including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO ) closely relate to air-ratio called lambda (λ) among all of the engine variables. Higher λ value indicates a significant amount of emissions harmful to our environment is produced and hence engine maintenance, particularly the catalytic converter, is necessary. Mandatory vehicle examination cannot be taken easily for each car, so it is difficult to enforce the vehicle owners on monitoring the health of their engines daily and taking immediate action to fix their vehicle emission problems. Traffic lights considered as "Things" through the concept of Internet of Things (IoT) can be applied because there are numerous traffic lights in an urban area. In addition, cars must stop on red lights so that reliable λ reading can be interrogated wirelessly through radio frequency identification (RFID). Simulation results show that the proposed application can effectively control and reduce vehicle emissions. © 2011 IEEE.