IvanV wrote: ↑Tue Dec 05, 2023 6:55 pm
dyqik wrote: ↑Tue Dec 05, 2023 5:51 pm
You should probably also consider the benefits to drivers of driving slower. Firstly, generally it costs less per mile - in fuel, maintenance, and in insurance rates (to the extent that everyone is driving more slowly, and thus safely, or with lower repair costs in an accident).
Secondly, it's usually less stressful.
Thirdly, it gives more mental space for non-driving thoughts - I may well have a very valuable idea in the extra couple of minutes on my journey that's undertaken at lower mental load.
Not true sadly.
Well not true in terms of fuel consumption. Fuel consumption is minimised around 50-55mph. So it increases emissions too. I don't know what it does to maintenance. But you won't be turning the engine slower at 20 rather than 30, you'll just be driving in a lower gear and for longer. Might be a bit less tyre wear. My maintenance is mostly time rather than distance driven - and I think that's mostly true of typical car per year distances.
Your figure here is for fuel consumption at constant speed. But fuel consumption in urban driving is largely driven by acceleration, with frequent stops and slowing. The lower speed you are accelerating to, the less fuel consumption in stop/start driving. Slower speeds also generally allow more gentle acceleration and braking, and may even eliminate some stops entirely, by allowing easier blending in and out of throttle. In particular, pulling out of side roads to merge with traffic is easier if that traffic is slower, and needs less net acceleration.
Maintenance on engines is driven by temperature cycles more than revolutions. A slower longer drive means better warm up and less time driving aggressively before the engine is warmed up, which reduces engine wear significantly. Maintenance on brakes, tires and suspension is speed dependent, as the loads increase significantly with speed.
IvanV wrote: ↑Tue Dec 05, 2023 6:55 pm
I don't find driving at 20mph low stress, I find it high stress. I find it hard to manage the car to maintain at that speed, the accelerator isn't very forgiving around there so my speed is never right. And I'm taking my eyes off the road to look at the speed all the time. The speedo isn't very accurate down there either. For that reason, there is actually more mental load.
You have more time to react to traffic, pedestrians, situation. It's generally lower stress, if you don't try and drive exactly at the speed limit.