HHO in Police and Emergency Vehicle Fleets: Case Studies

The Police Vehicle Idling Problem

Police patrol vehicles idle 6–8 hours per shift running HVAC, computers, communications, and emergency lighting. Idling fuel consumption is approximately 0.4–0.8 gallons/hour. A fleet of 100 patrol cars idling 7 hours per day consumes 280–560 gallons daily in idle fuel alone — $1,100–$2,200 per day at $4/gallon.

HHO in Idle Conditions

HHO at idle is less efficient than at driving load because the ECU operates at minimum fuel delivery and any EFIE offset has an outsized proportional effect. However, idle HHO installations that function primarily to improve combustion completeness (reducing carbon buildup and improving engine longevity) provide maintenance benefits even where direct fuel savings are modest.

Documented Fleet Programs

Several US municipalities have reported 8–14% fuel savings from HHO installation in police fleets in combination with idle-reduction strategies. The most successful programs combine HHO with anti-idling policies (engine off when HVAC not critical), battery backup systems for electronics during brief shutoffs, and driver training.

Implementation Challenges

Police vehicle modifications require approval from fleet managers, union agreements (in union departments), and typically FAA/DOT-equivalent fleet compliance review. Liability concerns about aftermarket modifications are the primary barrier. Municipalities with in-house mechanics and formal HHO programs bypass individual installer liability issues.