Its all about energy. Accelerating the cars up to speed is one thing, but slowing them down and negotiating corners is another. Whether you use batteries or diesel, speed always takes more energy. As for throughput, we need to know the safe distance between these things at various speeds. Just like on roadways, they need to be able to stop if the car/train ahead of them stops. So slower cars, closer together, probably result in more cars passing per second than at higher speeds with greater stopping distances between cars. Exactly the same as with roads.
Anyone who thinks that because these things are automated that they can safely travel bumper-to-bumper at high speeds hasn't worked with vehicles underground before. Any pileup in a tunnel is a nightmare. Something burning, especially something high-energy like butter or flour, turns the tunnel into a blast furnace. Safety distances will always be required.
https://en.wikipedia.org/wiki/Mont_Blanc_tunnel_fire
>>On the morning of 24 March 1999, 39 people died when a Belgian transport truck carrying flour and margarine, which had entered the French-side portal, caught fire in the tunnel.
Anyone who thinks that because these things are automated that they can safely travel bumper-to-bumper at high speeds hasn't worked with vehicles underground before. Any pileup in a tunnel is a nightmare. Something burning, especially something high-energy like butter or flour, turns the tunnel into a blast furnace. Safety distances will always be required.
https://en.wikipedia.org/wiki/Mont_Blanc_tunnel_fire
>>On the morning of 24 March 1999, 39 people died when a Belgian transport truck carrying flour and margarine, which had entered the French-side portal, caught fire in the tunnel.