Context:
I was having a ponder about a reply to a thread on the MML recently, and it got me thinking about the situation with Thameslink where it runs on 125mph fast lines, but the 700s have a max speed of 100mph, costing capacity. Short of some pretty impressive infrastructure interventions, the only way to avoid impacting the capacity on the fast lines is to stay off them entirely, or downrate them to the fastest common speed. In Thameslink's case, I was also wondering about the Peterborough services, which as a trade-off run with 110mph stock into the surface platforms at Kings Cross, and their equivalent on the MML, the EMT Connect services which also run with 110mph stock into the surface platforms at St. Pancras. Thameslink's Bedford services run on the fast lines and as far as I know, consume additional paths (so are presumably flighted to optimise this), but is this less of an issue as so few miles of the MML fast lines south of Bedford are currently rated for 125mph?
As far as I'm aware, the two gearing optimisation variables are basically acceleration and top speed, with the two extremes being metro where the train is optimised for rapid acceleration, but the lowest top speed (60mph for the underground, for example), or intercity, where they have the highest top speed (>125mph), but the worst acceleration. Given the need for identical performance profiles to make the most of capacity in the Thameslink core, I can see why the 110mph services cannot continue through the core, or have to consume extra paths on the fast lines if they use 700s.
Finally, the point:
Is there a reason why trains cannot have gearboxes with multiple sets of gearing? i.e. Metro-style gearing to get up to 60mph rapidly, then something like a clutch to disengage the gearing and coast whilst switching to the higher speed gearing? I presume there has to be a reason otherwise modern EMUs wouldn't have the set maximum speeds that they do (75/90/110/125) without needing to be re-geared to go faster. Is it just cost reduction, or is it actually impossible? I can't imagine why the 700s wouldn't have this if it were possible, given how new they still are and the constraints on the lines they run on.
I was having a ponder about a reply to a thread on the MML recently, and it got me thinking about the situation with Thameslink where it runs on 125mph fast lines, but the 700s have a max speed of 100mph, costing capacity. Short of some pretty impressive infrastructure interventions, the only way to avoid impacting the capacity on the fast lines is to stay off them entirely, or downrate them to the fastest common speed. In Thameslink's case, I was also wondering about the Peterborough services, which as a trade-off run with 110mph stock into the surface platforms at Kings Cross, and their equivalent on the MML, the EMT Connect services which also run with 110mph stock into the surface platforms at St. Pancras. Thameslink's Bedford services run on the fast lines and as far as I know, consume additional paths (so are presumably flighted to optimise this), but is this less of an issue as so few miles of the MML fast lines south of Bedford are currently rated for 125mph?
As far as I'm aware, the two gearing optimisation variables are basically acceleration and top speed, with the two extremes being metro where the train is optimised for rapid acceleration, but the lowest top speed (60mph for the underground, for example), or intercity, where they have the highest top speed (>125mph), but the worst acceleration. Given the need for identical performance profiles to make the most of capacity in the Thameslink core, I can see why the 110mph services cannot continue through the core, or have to consume extra paths on the fast lines if they use 700s.
Finally, the point:
Is there a reason why trains cannot have gearboxes with multiple sets of gearing? i.e. Metro-style gearing to get up to 60mph rapidly, then something like a clutch to disengage the gearing and coast whilst switching to the higher speed gearing? I presume there has to be a reason otherwise modern EMUs wouldn't have the set maximum speeds that they do (75/90/110/125) without needing to be re-geared to go faster. Is it just cost reduction, or is it actually impossible? I can't imagine why the 700s wouldn't have this if it were possible, given how new they still are and the constraints on the lines they run on.