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Path: utzoo!watmath!clyde!cbosgd!ihnp4!ihuxk!rs55611
From: rs55611@ihuxk.UUCP (Robert E. Schleicher)
Newsgroups: net.auto
Subject: Re: Most obnoxious driver awards
Message-ID: <1084@ihuxk.UUCP>
Date: Wed, 19-Mar-86 14:09:14 EST
Article-I.D.: ihuxk.1084
Posted: Wed Mar 19 14:09:14 1986
Date-Received: Fri, 21-Mar-86 04:16:34 EST
References: <515@mot.UUCP> <7700064@uiucdcs>
Organization: AT&T Bell Laboratories
Lines: 51

> 
> >>> One car length for each "60" mph???  I defy anyone out there to stop
> >>> a cycle going 60 mph in one car length (of course unless you run into
> >>> the back of the car, that should stop you rather suddenly!)
> >> 
> > Taking a car length to be around 15 feet, and since 60 MPH = 88 feet/sec,
> > you would have to apply your brakes within 0.17 seconds of the driver
> > in front of you in order for it to "work out pretty well."
> 
> You've assumed that the car comes to a stop instantly. The actual reaction
> time needed depends on how quickly the car and motercycle decellerate. If,
> for example, we assume that that 2 second figure for the car is accurate,
> that the decleration is constant, and that the motorcycle can stop instantly,
> then the motorcycle rider has just over 0.58 seconds to react. Does
> anyone know the real values for the braking times for typical cars and
> motorcycles?
> 
> 			Scott McEwan
> 			{ihnp4,pur-ee}!uiucdcs!mcewan
> 
The two rules of thumb mentioned are:

1.  A car lenght for every 10mph of speed (60 mph implies six car lengths)

2.  2 seconds of interval between cars

These two rules are approximately the same.  They are intended to
allow enough time for reaction to the car ahead stopping suddenly,
under its own braking power.  The rules don't work if your vehicle
has significantly longer stopping distances than the vehicle in front
of you (an extreme, but common example would be a semi behind a motorcycle).
The rules also don't work if something (like a cement wall) stops the vehicle
in front of you in a very short distance (although the rules may still give
you enough reaction time to take evasive action.

The two second/one car length per 10 mph rule was demonstrated to me once
in high school by using a car equipped with a buzzer, and a switch on the brake pedal.

While driving, the buzzer would go off, starting a stop watch.  The stop 
watch would be tripped by the first application of brakes.  Also, both the
buzzer going off, and the hitting of brakes caused the car to shoot a paint
blob on the pavement.  The results, over several drivers, bore out the
two second/one car lenghth per 10 mph rule.

Bob Schleicher
ihuxk!rs55611
:
> "I'm sorry, sir. According to your identification you're not even born
>  yet. Come back in 500 years."

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