> These things are for *our* protection, and we should all unquestioningly > embrace having a 0.001% less chance of death by redlight. On a side note, > in my hometown about 3 years ago they installed a trial one of these, but it > was continually shot out (I grew up in rural Kentucky). I never realized > the idea caught on elsewhere... I read a few online articles about it when > I realized it's for real and I find it disgustingly big-brotherish. Maybe > its time to take another trip to the ol' gun shop.... you know.... just in > case.... whats that? they're banning those too?! I feel a moralistic rave coming on. But not one without good engineering foundation. Fasten your seatbelts, set your cruise controls, we're off .... After just having suggested offlist to one poster that he may be treading on politically shaky ground (not that I care, it's not my stooge he was talking about :-) ) , I'll turn to a so far unproscribed area and add my 2 cents worth :-) I often hear people waxing lyrical over the inequity of speed cameras, red light cameras, traffic radar and traffic police in general. I do wonder what such people (and there is of course a range of opinions) would feel genuinely comfortable and happy with? No traffic rules? No speed limits*? - or perhaps limits but no enforcement. Maybe limits with very wide enforcement margins. (50 mph with 30 mph margin = typically 90 mph in town). I also wonder what they would do that they don't do now to protect their children under such utopian arrangements. I note that there seems to be a correlation between speed capacity of vehicle and probability of radar detectors being fitted. I am aware, of course, that radar detectors are fitted by responsible drivers to improve the safety of their driving (I just haven't worked out how that works yet). I note that a more recent safety improvement is the fitting of GPS and waypoint memory to radar detectors so that the driving may be even safer again - and I also so far have not been able to muster the intellect required to understand the no doubt simple mechanism by which this works. Social contract (whatever that may mean in this age) says that we give ourselves certain rights to kill a certain percentage of ourselves in exchange for the rights to expect a certain level of protection from ourselves. It's not as if there is some external authority who we are trying to beat. We are dealing with ourselves. The whole basis for the engineering of our environment stands on the social contract we have set ourselves. How clean the air, how fast the cars, how good or how often the safety checks, how polluted the food or how uncertain we are of what we are ingesting is set by ourselves. (We know that Mon$anto and their ilk will try and bend the rules at every turn in some of these areas, but lets stick to road safety in this diatribe.) If we all, or a clear majority, feel that the limits we have set are too restrictive, then we have the right and ability (in most countries at least) to stand up and say so and do something about it. If we think that more children should die on city streets so that we can get home sooner, or if we think that changing our driving behaviour won't change how many children die, or if we think that enforcement mechanisms are inefficient or wrongly targeted, then we have the right and the ability to do something about it. If we think we'd rather have arguably safe nuclear power and leave the problems to our children's children in place of unquestionably unsafe coal power which gives us problems now then we have a right to do something about it. If instead we simply do what we wish, or attempt to, or wish to then we are stealing, attempting to steal or wishing to steal the benefit of the agreed social contract from ourselves - or from the portion of ourselves who don't. If we ALL do this then it's just money in the government's coffers, and SOMEBODY has to fund us, so who cares. (Less government-ers, tax is theft-ers, enclave isolationists and others** may stand up and be counted here :-) ). And of course, more dead children all round, but if we all do it then we have just modified the social contract and we're all happy. The major problem is, that the child struck by the car which would have been able to stop if it had been travelling at agreed-social-contract mph, or the person broadsided by the "why shouldn't I run late orange was-that-REALLY-red-officer? lights if I want to" free-thinker is usually not the person who has bought into the social contract initially. Each year the US kills more of its citizens in road "accidents" than died in the whole Vietnam war, over 10 time as many as died in "911" and far far more than will die in Afghanistan & Iraq, no matter how many more that may yet be. (43,000 auto fatalities USA 2003, almost 3,000,000 injuries.) (NHTSA early assessment for 2003 - interesting) ( http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NCSA/PPT/2003EARelease.pdf ) But, my constitutional rights, it's only done to fill government coffers, everyone does it, radar detectors for safety,... & more mean that's not liable to reduce appreciably anytime soon. For a little perspective, the US death rate per car is less than for France and half as much as Portugal's. For a bit more perspective, the death rate per capita (a more real measure) is worse than for France but not quite as bad as Portugal or Greece. I suppose one could be proud of having a better death record than Greece. Or Portugal. (Have you ever seen spectators at a Portugese rally ? :-) !!!! ). US fatalities per capita which are 2.5 times a high as UK suggests (only suggests) that the unreasonably strict tolerances on speeds on their motorways and their obnoxious bobbies MAY just be doing something. So the USAites can laugh, NZ's record is slightly WORSE per capita than the USA's. _______________ Few people (even engineers) seem to appreciate how much more damage a car travelling only "slightly" faster will typically do to a pedestrian. Fatality rate (McMahon empirical formula) is approx % killed = V^2/5000% V in kph or % killed = V^2/1800% V in mph. Above 100% death is essentially certain. eg at 50 kph %death = 50^2/5000 = 50% at 70 kph =~ 100% A car travelling at 70 kph will kill about 50% of the ball chasing children that the same car travelling at 50 kph just manages to stop for. A car travelling at 60 kph will kill over 20% of the ball chasing children that the same car travelling at 50 kph just manages to stop for. What may not be intuitively obvious without having thought about it (even to engineers) but which is obvious on reflection, is that if two identical vehicles, which have a speed difference of V mph, start braking together, then when the slower one stops, the faster one will be still travelling at MORE than V mph. Possibly much more. This is because the energy in the vehicle accumulates with the square of the speed and the extra speed adds substantially more than linear energy. As an example, two cars travelling at 70 & 50 kph start braking together. Assume that the brakes can remove energy at a constant rate. In practice brake fade etc may make this assumption invalid - which leads to a worse result. Car A at 50 kph has 50^2 = 2500 units of energy. Car B at 70 kph has 70^2 = 4900 units of energy. When car A has just stopped car B has (4900-2500) = 2400 units of energy left so is travelling at sqrt(2400) = 48+ kph (!!!!). ie A 70 kph car will hit at about 50 kph an object that a 50 kph car can just stop for !!!!. Reaction time makes this worse as during reaction time car B travels further so has less distance to brake in. As covered in more detail below - Car A CANNOT kill the child which it just fails to hit. Car B will kill the child about 50% of the time. There are some assumptions that vary the end result eg reaction time, whether the car can decelerate at constant g or at constant energy reduction rate or .... . Whatever the assumptions - if a 50 kph car JUST stops a 70 kph car will hit at around 50 kph - maybe more. (Constant energy reduction should be a reasonable assumption. Unless you are at maximum coefficient of friction point then brakes should be working as hard as they can which should be a constant rate until they begin to fade. At brake locking point the best that can be achieved is about 1g (depends on car) so that could also be used as a best case assumption). At 50 kph impact you kill 50^2/5000 = 50% Hey - that's not so bad. 50% odd live! But every dead child is one outside social contract. If you ever kill one in such circumstances you should feel (as you are) responsible for the rest of your life. There are, of course, ways to feel better about this. Should have looked first, parents didn' bring them up to take care, they KNOW people drive fast through here, they shouldn't have been allowed to play with a ball on such a busy street, my car had superb performance and excellent brakes and my reaction times are so swish hot that an ordinary car/driver would have killed them anyway,... . The social contract, as currently implemented, assumes that all drivers and vehicles are equal. It gives good drivers and good vehicles a chance to improve the safety of others. I would not like to bet that "good" drivers with "good" cars only equal out the equation when they decide to make themselves as dangerous as the average car/driver. The velocity^2 energy rule brings the BMW into normal territory faster than most would realise. (if YOU dispute this - do YOU believe the analysis above that says that 50% of people that YOU would have just missed will die if YOU are doing 70 rather than 50?.)(If not, explain why). Have I ever hit a person while driving a motor vehicle? Yes and no - I'd laid the motorcycle on the road by the time I hit the running child - and I wasn't speeding. And they weren't severely hurt. Still doesn't feel very nice (for them or me :-) ). Do I sometimes exceed posted speed limits? yes. Run the occasional red light? - er, yes. Make excuses for why I do it? No. It's indefensible. Is it safe enough? - often, yes. Aren't there occasions when the posted limits don't make sense? - yes, BUT when they don't make sense and then an "accident" happens, it's no accident. But of course there are lots of explanations. How was I to know that there would be a kid there at that time in a weekend?! - this place is ALWAYS deserted in weekends !!! Who would have thought that anyone would have been coming through that intersection at that time of night? Hey! - I drive a BMW/Mustang/Lamborghini/Unimog :-) / Have been driving for 60 years/have a clean record / am a Mason (where'd that come from) ... Dead. My little girl is dead!? What happened??? Rerun above excuses. And I wonder how many who feel utterly frustrated by tightly controlled speed limits (like our British brethren seem to) have worked out how much difference it actually makes to trip time to travel at say 100 kph versus 120 kph. Or around town at 50 vs 60 or 70. In Arizona I'm told that people cruise at 100 mph plus. Didn't see any. May have been due to the spotter aircraft signs ? But, I did like the autobahns * :-) Russell McMahon (who really hopes he won't now go & do something stupid in a car and kill anyone in the next while) _______________________________ For a NZ article that explains that increased speed does NOT result in more deaths, see http://www.investigatemagazine.com/july00speed.htm :-) ______________ * In Germany on the autobahns there are indeed no speed limits. And it all looked and felt very safe. When we were there last year, cruising at 130 - 140 kph (80-90 mph) we had people passing us at 100+ kph deltas (!). Sit in the outside lane more than a few seconds too long at 130 kph and you have a Mercedes glued on your rear bumper until you pull into the "slow" lane. While there are no speed limits, there are definitely rules AND everyone seems to abide by them. The roads are built to suit. When they do have accidents, and of course they do, the probably have less problems with getting people to hospital than we do here. Elsewhere in Germany there are very strictly controlled speed limits - some quite conservative. Heavy vehicles have their limits for each class of road displayed prominently on the back so authorities can see at a glance whether they are doing as they are intended to. ** I thought about saying "... other whingers ..." there, but I'll leave it to the footnote readers to decide if that was wise :-) . *** Congratulations if you got this far :-) -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads