During the first motorcycle chase, Hooker and Romano enter the freeway going the wrong way. In the close up shot, the background behind them is a regular street.
In the close up before the police car crash, neither Hooker nor Romano are wearing a seat belt. The car goes airborne and smashes nose first into the ground. Neither officer is injured. In fact, an impact of that nature would have propelled Romano through the windshield and Hooker into the steering wheel. It is likely one or both officers would be dead.
The side number on the car Hooker and Romano crash is 49357 (seen as they are taking the initial vandalism report immediately before the pursuit and crash). This same side number is seen on the replacement unit they are using, indicating another car was actually crashed.
The police car used for the crash clearly has no gas tank- the tank strap can be seen swinging in the air as the car goes airborne. Removal of the gas tank for car crashes was a standard safety procedure used for stunts of this nature.
At the second homicide scene regarding the motorcycle, Romano makes two errors- a skid mark is a mark left in the road when a vehicle is slowing down and the tire is sliding on the road. An acceleration mark is left as the vehicle accelerates and the tire spins on the pavement. Romano called the mark seen a skid mark when it was clearly an acceleration mark, something a city police academy graduate would know. His second error is calling the piece of the lever found a handbrake lever. As someone that self-proclaimed to have motorcycle experience, he'd know the piece found based on the direction the motorcycle was facing was part of a clutch lever, not the hand brake, which is on the opposite side of the handlebars.