"Loud pipes save lives". The statement would seem to be axiomatic based on the sheer volume of its repetition. On the surface it seems obvious that the noise emitted by loud motorcycle exhaust systems would aid in conspicuity and cause more watchful driving by other motorists. Yet not a single thoughtful study has been done that supports the theory. To the contrary, the two types of bikes that most often use loud pipes (cruisers and sport bikes) are significantly over represented in crash data (accidents per type vehicle mile).
And what about hotrods? Surely their hulking size and eye-catching flame paint jobs don't need help from loud exhaust systems to be noticed. Do drivers of cars with booming sound systems have safety in mind? Aside from showy cosmetics and oppressive noise emissions, one thing that the owners of these vehicles have in common is an aggressive, even anti-social presence on public road ways; most notably a constant revving of the engine, particularly under heavy throttle load.
The mechanism that binds the various people and their behaviors is a physiological condition known as acute stress response or "fight or flight" response. Most often induced by loud noise, flight or fight is an involuntary reaction that cannot be controlled by conscious thought. When triggered, release of the stress hormone cortisol causes an array of metabolic changes including an instantaneous increase in cardio- respiratory rates and muscle tension. The state of arousal is perpetuated by a release of dopamine, endorphines, norepinephrine and epinephrine (adrenaline). Most importantly chemical releases (catecholamines) suppress activity in the area of the brain concerned with short term memory, concentration, inhibition and rational thought; 'flight or fight" reactions require spontaneity and aggression. Is this really the optimum state of mind to be in while perched atop a machine that can abruptly reach triple digit speeds with the jerk of a wrist?
The high motorcyclists get from stress response may be the perfect elixir to get them in the mood for a Sunday afternoon romp around town. Unfortunately, though, the metabolic spikes are most unwelcome to anyone trying to relax or sleep or even engage in the ordinary activities around the home. Left in the wake of a typical loud pipe ride are hundreds or even thousands of citizens who are literally made ill by the toxic effects of stress response.
One of the more intriguing aspects of flight or fight is the compulsion to goad others by abrupt stimulation. Any martial arts combatant knows that a loud, piercing scream can thrust his opponent into a physiologically induced state whereby the opponents' actions may be manipulated and/or impulsive. This, even though the opponent is trained to expect the ploy. Is it wise to create a stressful driving environment when surrounded by vehicles many times your size and mass?