In an age of increased environmental awareness, new commitments to reducing emissions and pollution in the air, Crowley has invested in engine modifications on its 10 tugboats dedicated to the Puerto Rico/Caribbean liner service and on its four tugs chartered to Trailer Bridge for their Puerto Rico barge service. Crowley makes four to five trips per week between the United States and Puerto Rico, which provide ample opportunity to test and perfect engine modifications, which have led to lower exhaust emissions and increased performance. Exhaust emissions take on a number of forms including visible smoke, particulate matter and nitrogen oxides (NOx). Crowley is working to reducing all three while achieving heightened performance with decreased fuel consumption.