Understanding Speed Limits
Know Your Speed Limits
UK Speed Limits
Speed Limits
80mph limit criticised
Oil Production Increase
Economical Driving - The Physics
A limit to the highest legal speed for a particular road is
not necessarily
a safe speed. It is the
maximum speed permissible.
Philip Hammond (Transport Secretary) said the current limit
(speed on roads - DA), introduced in
1965, was out of date due to
"huge advances in safety and motoring technology". This is pandering to the car manufacturers and conveniently ignores protecting road users be they driver, passenger, pedal cyclist or pedestrian. Drivers
'controlling' cars capable of high speed include the inadequate driver who considers him/herself a
Stig.
Talking up the improved safety in cars
does not consider that reaction speed remains
unchanged. The time available to react to a situation is
reduced for a particular driver as the faster the car is travelling the further the vehicle will have moved
before any avoiding reaction to the situation can be made. Reaction speed and time involves recognising a hazard and making a decision about the necessary action to be taken. If the wrong decision is made then it is unlikely that time will be available to correct the error. The higher the speed the less chance of corrective action. The inevitable is a
negative outcome and possibly
(probably - DA) a fatal one if travelling at
80mph or even ‘just’
70mph. Seat belts aren’t particularly effective
above 30mph or thereabouts.
A real advantage of a rear seat belt at survivable speed is restraining a human missile (child or adult) thrown forward in the event of rapid deceleration after collision impact.
- Motor cyclists are excluded since they form a totally different argument. Of those who ride powerful motorcycles, many (probably the majority by far - DA) seem to imagine themselves exempted from laws that apply to everyone else. As an estimate of all RTA (road traffic accident), bikers amount to just 1% of road users, but account for 25% of those killed.
Statistics intended to describe the situation do not clarify reality. The apparent reduction in the number of fatalities
(per billion vehicle miles) fails to consider that the number of road users over the same period increases. The logarithmic scale distorts the picture considerably. This is a similar distortion (though not erroneous) to the apparent violence of an earthquake. The
Richter magnitude scale is logarithmic and an increase of a
single unit is actually a
x10 increase in the severity. A change or
5 -> 6 = x10 and
5 -> 7 = x100. Radiation exposure is also logarithmic
(exponential). A danger with statistics for the unaware.
70 miles in
1 hour against
80 miles in
1 hour is simply an increase of
10 miles distance in the same
60 minutes. At the same speeds, a distance of
7 miles would take
6 minutes (360 seconds = 70mph) and
8 miles also
6 minutes (80mph). Put another way, the same
7 miles at the higher speed would take just over
300 seconds = 5 minutes. The journey would be shortened by
1 entire minute.
- Hold ups (junctions, roundabouts, traffic lights) and other speed-affecting problems would easily neutralise this 1 minute
Advances in technology are claimed to have made cars much safer, contributing to a drop of more than
75% in the number of people killed on British roads since the
70mph limit was introduced. A drop of
75% may describe a 'reduction' in total numbers, but does not indicate the number of fatalities on British roads. As the number of
'users' increases, the
75% decrease is of an
increasing quantity.
Green Party spokesperson Jenny Jones:
"This is a mad idea just at the time we should be worrying about fuel economy and emissions. Putting the speed limit up will be worse for both. So much for the 'greenest government ever'." (Most backward and growth driven - DA)
Economical Driving
Hammond is the government champion of
increased speed. Getting from
A to B just a bit quicker. If this
'bit' is hundreds of miles away then travelling by plane can have true meaning
(ignoring the pollution issue, the vast quantity of fuel used, travelling to an airport... - DA). If just a few miles away, then increased speed of travel does not 'quicken' the total journey by much.
Many complain about the rising cost of fuel. Many do not and make considered moves to
reduce their costs The fall in petrol sales 'cost' the Treasury nearly £1bn over the six months to June. (It doesn't cost the Treasury anything as it's just revenue that
never materialises -
DA). Some of those who do complain are deluded and is evidenced by the
uneconomical driving techniques. Racing around with
hard acceleration of large-engined vehicles. The increased fuel consumption is enormous and the time savings negligible on short town journeys. Government loses out on tax revenue with the rise in numbers of careful drivers. This explains the requirement to
'sell' more petrol. It’s a vicious circle: the cost of fuel escalates so the number of
economical drivers increases and tax revenue decreases as consumers are getting smart. But
not smart enough. Government
ensures fuel prices rise to compensate
(they really do ‘influence‘ -
DA).
The environment and conservation of global oil
'reserves' do not matter and is suggestive evidence that there is
no actual long-term shortage. The growing air travel business also conflicts with both of these arguments. Just the
continuing and
self re-enforcing message that there is a shortage to justify rising costs for all.
There are some fascinating statistics put out by Jaguar for their
XF saloons. All mixed up between the two extremes of models, from the cheapest diesel powered
XF Saloon 2.2D SE (£30,950) to the most expensive
XF Saloon 5.0 V8 SC XFR petrol engine model
(£65,350). It's really about comparing what you get (or expect to get) for your money. Consider:
0 -> 60 mph in 8 seconds or
4.7 seconds. Although it appears to be roughly twice as fast to accelerate, actually the slower one takes just an additional
3.3 seconds. But it's
£34,400 cheaper. Not really much of a speed advantage for such a huge cost overhead. But then the
extra £34,400 enables a top speed of an
additional 15mph (140mph -> 155mph). This works out at about a
10% maximum speed increase for the additional
110% purchase price for the performance advantages of almost
double the standard acceleration
4.7s v
8.0s (0 -> 60mph). Moreover, town driving returns
15.1mpg (
V8) against
42.8mpg for the
2.2D. Comparative out-of-town driving yields
32.4mpg and
58.9mpg, respectively. These are the official Jaguar figures even though they are extraordinary.
Rolls-Royce unveiled the
£305,000 gas-guzzling British-built
Phantom Drophead Coupe. Arguably the safest convertible in the world. With a
kerb-weight of
three tons, the massive
6.75 litre V12 engine will propel it from rest to
62mph in just
5.9 seconds. There is a claim that
17 miles to the gallon is achievable from this two-door four-seat convertible
'fast tank': 3 tons taken from
0 -> 62 in 5.9 seconds? More like
2-3mpg? Someone who can afford the RR in the first place is unlikely to be bothered by consumption figures. Exhaust emission would be vast. The six speed car develops
453 brake horse-power - about the same as five Ford Fiestas - though the top speed is being electronically limited to
149mph (why bother? - DA). Road wheels are claimed to run for
100 miles at
50mph when punctured - eliminating the need for a spare.
A psychological trick: RR vehicles don't get punctures and don't need spares
(you can imagine the salesman telling that one - DA!!). The problem is, of course, that the slow puncture carrying
three tons won't be noticed until the tyre is dangerously flat.
70mph -> 80mph = 14.28% increase in speed and the kinetic energy (caused by motion) is given by
½mv². The energy is related to the
square of the speed and
½m(70 x 70) = 2450 and ½m(80 x 80) = 3200. The
dimensions for mass and velocity cancel out leaving the comparison simply between
2450 and
3200 that represents a
30.6% increase. The increase in speed has
more than a
doubling of the corresponding collision energy. The impact on crash is
much greater and consequently the survivability of the higher speed crash is
much less.
