Denver: Police departments across the country are ordering officers to pair up after ambush attacks left eight officers dead in Texas and Louisiana.
Officers say it's an important safety precaution.
But doubling up could also slow response times to low-level crimes and drive up overtime for already exhausted officers.
Los Angeles police assigned members of specialised crime-fighting units to back up officers answering calls for service.
Baltimore police began sending two squad cars to every call.
Dispatchers in Denver urged officers to travel in pairs indefinitely.
Some agencies are even telling officers to pair up on breaks.
Sgt Bryan O'Neill of Denver's Police Protective Association says officers are working hard to ensure calls for service don't back up and police stay visible on the street.