This disclosure is generally directed to systems and methods for optimizing a travel route of a hybrid-electric vehicle inside an emissions-free zone. In one exemplary embodiment, a travel route optimization system can be used to determine a charge level of a battery in the hybrid-electric vehicle and to locate charging stations inside and/or outside the emissions-free zone. The charge level provides an indication of a distance that the hybrid-electric vehicle can travel before a gasoline engine is started. The system can use factors such as the location of the charging stations and the charge level of the battery to generate an optimized travel route for the hybrid-electric vehicle that eliminates starting of the gasoline engine inside the emissions-free zone. The optimized travel route may be updated in real-time so as to allow recharging of the battery on an as-needed basis at a charging station inside or outside the emissions-free zone.