The 20 mph Discussion
- Thread starter 1finny
- Start date
There's a lot of "evidence"/arguments for both so it's not conclusive. The slower you are going the more time you spend in an area so there is an argument that causes more emissions. Travelling at a constant speed of 20 or 30 there is very little difference. Most of the emissions are caused during acceleration and it takes more to accelerate to 30 than it does 20. Driving in 30 (or 20 areas) compared to motorway driving typically has a lot more frequent acceleration and deceleration so anything that minimised the amount of acceleration/deceleration cycles should reduce emissions. It also reduces tyre/brake particulates. That's why 20 zones controlled with speed bumps are not the best for environmental reasons. Electric cars change the conversation a bit because their emissions are the same at any speed.I did read that but can’t find much evidence - if it’s true I’d like it to be transparent.
It’s funny how ‘saving the environment’ comes into play at times this
SmallTown
Well-known member
Their energy consumption is lower though at the lower speeds. Saving electricity in the long run
Muttley
Well-known member
From my experience of driving in Wales (albeit in the North tourist-y bits) it doesn't take long to adjust. In a manual car you just stay in 3rd.
I would expect emissions to be little different, "sleeping policemen" and similar devices make more of a difference as you brake as you approach them, generating particulates and accelerate after them generating CO2 etc. Driving at a constant speed is a simple mathematical equation how much power is required to move a two ton object at the relevant speed.
The simplest statistic is this. If you hit a human being at 20mph they will probably survive, if you hit them at 30mph it's 50:50, and if you hit them at 40mph you will likely kill them. Residential streets should always be driven at 20mph whether the law states it or not. Arterial urban roads 30 and urban roads with no residential or commercial properties adjacent, 40.
I would expect emissions to be little different, "sleeping policemen" and similar devices make more of a difference as you brake as you approach them, generating particulates and accelerate after them generating CO2 etc. Driving at a constant speed is a simple mathematical equation how much power is required to move a two ton object at the relevant speed.
The simplest statistic is this. If you hit a human being at 20mph they will probably survive, if you hit them at 30mph it's 50:50, and if you hit them at 40mph you will likely kill them. Residential streets should always be driven at 20mph whether the law states it or not. Arterial urban roads 30 and urban roads with no residential or commercial properties adjacent, 40.
1finny
Well-known member
Sounds right to me
And, ripe for a wonderful ethical discussion on the merits (or not) of saving the planet by keeping the 30 mph at the extent of lives - which also maybe good for the planet in the long run
(maybe for another day tho
)I was talking about direct roadside pollution but yes that is a factor. Although, interestingly it isn't always the case. It is affected by temperature. When the weather outside is very cold (or very hot) the range (and therefore the energy consumption) is affected so using the car for longer at a slower speed uses more energy than a higher speed for less time. In the chart below you can see that the peak range at 20deg is about 20mph but at 0deg and 30deg it is over 30mph.
Corcaigh_the_Cat
Well-known member
The 'poor drivers' talked about on these threads use motorways too.
70 is plenty on our motorways. There's no reason to be travelling in excess of that, although we've all done it. Cars have been able to travel faster than 70mph throughout my lifetime, I'm in my late 60's.
Boro_Interlinked
Well-known member
Austin Metro excluded... maybe expand that to all of British Leyland too
Marineboysmoggy
Active member
And what about the two junction on it and in the area.?
Trying to judge speed is bad enough when pulling out now.
newyddion
Well-known member
If the clocks in Great Britain shift forward by one hour throughout the year – to GMT+1 in winter and GMT+2 in summer.
Single Double Summer Time (SDST) We would cut our carbon emissions by at least 447,000 tonnes every year, save around 80 lives on the road, create 60,000–80,000 new jobs, cut crime and give us more time for sport, barbecues and other outdoor activities.
Making evenings lighter saves lives. Because most people tend to make longer and more complicated journeys after work and school than they do at the start of their day, it’s safer for them to make afternoon and early evening journeys while it’s still light outside. In fact, the Royal Society for the Prevention of Accidents (RoSPA) estimates that we’d save around 80 lives each year by making these changes. Children between the ages of 5 and 15 and elderly people are the groups likely to benefit most from the change.
During the British Standard Time experiment, road casualties dropped substantially. It’s true that there was a slight increase in the number of deaths on the roads in the darker mornings, but these were more than offset by the much larger (and mostly unreported) decrease in deaths during the brighter afternoons and early evenings. That’s why leading road safety experts agree that shifting the clocks forward would be a good idea.
Single Double Summer Time (SDST) We would cut our carbon emissions by at least 447,000 tonnes every year, save around 80 lives on the road, create 60,000–80,000 new jobs, cut crime and give us more time for sport, barbecues and other outdoor activities.
Making evenings lighter saves lives. Because most people tend to make longer and more complicated journeys after work and school than they do at the start of their day, it’s safer for them to make afternoon and early evening journeys while it’s still light outside. In fact, the Royal Society for the Prevention of Accidents (RoSPA) estimates that we’d save around 80 lives each year by making these changes. Children between the ages of 5 and 15 and elderly people are the groups likely to benefit most from the change.
During the British Standard Time experiment, road casualties dropped substantially. It’s true that there was a slight increase in the number of deaths on the roads in the darker mornings, but these were more than offset by the much larger (and mostly unreported) decrease in deaths during the brighter afternoons and early evenings. That’s why leading road safety experts agree that shifting the clocks forward would be a good idea.
SmallTown
Well-known member
Not safely no:
A modern car has so much in terms of safety features compared to a car back then:
Massively improved brakes, suspension, steering, and Tyres that are incomparable in grip compared to the crossplys we had back then.
Most new cars also have active safety systems, ABS, Stability control, and even auto braking, blind spot alerts, sensors checking for incidents.
All those tonnes of feature will dramatically reduce the chance of you being in an accident in the first place. But, when you do (because drivers are indeed idiots) cars have crumple zones, safety cells, anti submarine seatbelts, airbags, they are basically tanks compared to older cars.
Both things will be unpleasant and probably deadly but given the choice between being in an accident at 60MPH in a 1960s car or 80 MPH in a brand new car. I'll take the brand new car all day long.
Corcaigh_the_Cat
Well-known member
All true, but drivers weren't distracted back then by mobile phones, digital stereo systems and sat navs. Sure you can pull into a service station to use/adjust them but how many do?
SmallTown
Well-known member
I agree. Drivers are terrible these days. But cars are not and they are just so much safer to drive at high speeds. A few years ago I drove to a friend's wedding and did sustained speeds of around 120MPH and it felt perfectly safe and stable.
newyddion
Well-known member
Far too many variables for you to be safe going at 120mph regardless of how it felt.
ThePrisoner
Well-known member
If your engine is at 2000 rpm in 3rd gear at 20 mph to cover the same distance as it otherwise would at 1500 rpm in 4th gear at 30 mph, then the vehicle will burn more fuel and have higher emissions as it's at higher revs for longer time. It ain't rocket science. Just look at the mpg numbers on your instrument display.
Corcaigh_the_Cat
Well-known member
The car isn't in control.
JM14
Well-known member
Just look at peoples attitudes to speed vans to see the uphill battle with making roads any safer. Full of self importance and too selfish to change their driving habits usually until it’s too late.
I would love to see every residential school area limited to 20 with speed cameras everywhere with increased fines for anyone caught, but imagine the backlash if people are delayed by a couple of minutes on their journeys. We see road deaths every single day and standards seem to be getting worse if anything
I would love to see every residential school area limited to 20 with speed cameras everywhere with increased fines for anyone caught, but imagine the backlash if people are delayed by a couple of minutes on their journeys. We see road deaths every single day and standards seem to be getting worse if anything
SmallTown
Well-known member
Ah ok. Well just ignore the bit I said about safety systems. Cool cool
JM14
Well-known member
doing those speeds presumably on a UK road means you’re the terrible driver here
Doing double the speed of other cars on the same bit of road is just asking for a disaster
Redwurzel
Well-known member
My Metro 1275 could do 100mph - I never did it, but it was not a slouch. There was a MG version too that was a reasonable rally car in the mid 1980s.
Also some older cars from 1970s and 80s did not have things like catalytic converters, air bags, electronic displays, as much electronics, rear seat belts, head rests, thick plasticy paint, so they possibly weighed less.
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