The real life Special Investigations Unit of the SFPD (known as the Special Investigation Division) does not handle cases like those portrayed in the show. The division is tasked with roles such as the mayor's security detail, bomb squad, and dignitary protection.
Captain Bridges carries a highly customized 1911A1 as his service weapon. This along with the weapons carried by Inspectors Dominguez (Ruger P89, SIG 226, SW99), Leek (Glock 17), Cortez (Smith & Wesson 659), Babcock (Smith & Wesson 4506) and McCabe would not be authorized for on duty use. The official issue sidearm for sworn SFPD personnel at the time was the .40 caliber Beretta 96GT.
The San Francisco Police Department--or any police department, for that matter--would not allow its employees to drive such an expensive vehicle for routine police work.
Although Nash Bridges' car is referred to as a 1971 Plymouth Barracuda (the grille/headlamp, mirrors, and tail light configuration is that of a 1971 Plymouth Barracuda.) The actual cars used were 6 Total, (5) 1970 Plymouth Barracudas and (1) 1973 Coupe (used as FX Car)converted to look like 1971 Hemi Cuda Convertibles. None actually had a Hemi motor, but rather 318-440 motors. 2 stick and 4 automatics.
Almost every episode features scenes of Nash and Joe driving through the streets of San Francisco, seemingly never having to stop for red lights. If you look closely in the background, as they drive past major intersections, you can often see actual San Francisco motorcycle cops holding back traffic to allow the scene to be shot, thereby enabling Nash to drive through the City without ever stopping.
Nash Bridges 1971 Plymouth Barracuda "Hemicuda" was at the time and has been the most expensive production vehicle on the classic muscle car market. The vehicle was worth at least $450-700k in the 1990s and is now $2-3 million USD for the 15 known models.
Officer Ronnie wears sergeant's stripes; he should therefore be referred to as 'Sergeant Ronnie'.