Unpopular but necessary policy on speed limits?...

[Benson]

That's a good point and I have.

I don't believe capacity (vehicles per hour past a given point) will be adversely affected.

This seems counterintuitive at first.

If cars traveled with a set distance between them regardless of speed then higher speed would mean higher capacity.

But cars don't. The distance between cars is a function of reaction time and stopping distance and is a time based value eg 2 seconds. In fact this time increases slightly with speed as the stopping distance component dominates over reaction time.

So the net effect is capacity is broadly flat and even increases slightly as speed limits decrease. And this is before you take into account the huge effect of "phantom jams" on capacity. These tend to increase as speed limits go up.

Traffic congestion is not caused by speed limits being too low - do you think our motorways would have higher capacities if we upped the speed limit to 90mph? Would town centers be clearer if we upped the limits to 60mph?  It's other things like junction design, light phasing, driver behaviour etc that cause congestion.

With EV's and their onboard software, the car should only start once the insurance cover has been downloaded to the vehicle from the insurance company over your wi-fi.

Then each EV has a built in black box. This tells the insurance company the metrics of your driving; acceleration, corning, GPS speed etc.. Each breach causes the insurance to rise but each increase takes years to decrease. Just means people pay on how they drive, the greater over the highway code someone goes, the greater their insurance is. Imagine someone on £20 a month and by the end of the year, they pay £100 a month. Then the year after, they hit £400 per month. By all means don't pay, but then the insurance policy stops the car because the insurance company couldn't automatically renew it each month.

The technology is on the way, forget about VED etc.. the government should just cream off their share of the insurance payments. The way I see people drive about on the roads, this idea will sort out a lot of idiots.

[BeElBeeBub]

BBB
Have you considered the extra congestion that this will cause on Motorways and other roads? The reduction in speed will mean that there will be 40% more cars on the motorways, as they will need longer to complete their journey.
This will clog up our road systems even more than they are at the moment.

That's a good point and I have. 

I don't believe capacity (vehicles per hour past a given point) will be adversely affected.

This seems counterintuitive at first. 

If cars traveled with a set distance between them regardless of speed then higher speed would mean higher capacity. 

But cars don't. The distance between cars is a function of reaction time and stopping distance and is a time based value eg 2 seconds. In fact this time increases slightly with speed as the stopping distance component dominates over reaction time. 

So the net effect is capacity is broadly flat and even increases slightly as speed limits decrease. And this is before you take into account the huge effect of "phantom jams" on capacity. These tend to increase as speed limits go up. 

Traffic congestion is not caused by speed limits being too low - do you think our motorways would have higher capacities if we upped the speed limit to 90mph? Would town centers be clearer if we upped the limits to 60mph?  It's other things like junction design, light phasing, driver behaviour etc that cause congestion. 

[Barry]

BBB
Have you considered the extra congestion that this will cause on Motorways and other roads? The reduction in speed will mean that there will be 40% more cars on the motorways, as they will need longer to complete their journey.
This will clog up our road systems even more than they are at the moment.

[papasmurf]

Hence my proposal of a 50mph national speed limit.

Gets a more comfortable chair, nibbles and drinks.

[BeElBeeBub]

Despite my (on here at least) minority anti-brexit feelings I suspect this might be my most unpopular opinion! 

So, background.

The shift from internal combustion vehicles to battery electric for large parts of the domestic passenger car sector is underway.  Yes there are some applications where ICE vehicles still make better sense in lots of ways, and charging infrastructure needs investment, but for the majority of people buying new cars the calculus is shifting.  It is plausible that the vast majority of new car sales will be BEVs by the end of the decade if not sooner.

BEV's have a problem, often pointed out, with range.  This mainly stems from the energy density of the batteries which is improving but slowly.

To get long range you need sufficient energy storage, which means you need a certain amount of battery material, this adds weight, size and cost.  The added weight makes your efficiency (miles per kwh) lower so you need even more battery.  A vicious circle. The GM Hummer electric has a 200kwh battery that weighs as much as a Honda civic, to achieve 200 miles range 

Long range is only a requirement if you are doing a long journey.  Short journeys allow for recharging between trips, say at home.

Long journeys are typically conducted at higher speeds, eg motorway.  BEVs tend to have lower ranges the faster they are driven.  Thus your range is actually lower on long distance journeys.

Which comes to my point......

The biggest determinate of driving efficiency is air resistance.  It accounts for the majority of the energy requirement.  At car type speeds it scales with the square of the speed.  Go 2x as fast and you need 4x the power.

Conversely, go 1/2 the speed, use 1/4.

If we set the national speed limit to 50mph vs 70mph the air resistance of vehicles would be about 1/2 and the range would be increased by around 40%

So a car with a 200mile range would now have nearly a 300mile range.  With no additional battery.  Additionally, if all vehicles were doing 50mph, the car can be lighter and still be safe (energy in collision also scales with the square). The acceleration can be achieved with lower power motors, which themselves are smaller, lighter and cheaper.

Recharge times also become quicker because the charge rate is effectively miles added per minute, and if you do 40% more miles per kwh added, your effective charge rate goes up by 40%

Cars could have a 210mile range with battery packs of 30kw, which could charge in under 15 minutes from a 150kw charger (fast charge chemistry allowing) and overnight from a standard wall plug.

Of course, nobody wants to be driving a 50mph lightweight car o nthe motorway with 3t pickup trucks barrelling by at 70mph+

Hence my proposal of a 50mph national speed limit.