Quote:
Originally Posted by goodgrowth
Are there any legit train nerds on here that can answer the question if there is an optimal train speed before you get diminishing returns for your money for more speed?
Presumably a 200km/h train costs less than a 300km/h train no?
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There's more than one factor beyond speed. There's also the distance between destinations served, the population around the potential stops, what - if any - infrastructure already exists, and the geography of the potential route(s). Speed does tend to cost more because a) the route needs to be more level and more straight the faster one goes and b) jurisdictions require greater safety measures with higher speed since accidents are more catastrophic as speed increases. Perhaps the most expensive safety feature is the crossings which require more robust crossing gates for high(er) speed rail while they need to be removed entirely for full HSR.
With distance, if the population is spread fairly evenly across a route that means you need more frequent stops which negates the benefit of really high speed since there's not enough time between stops to allow the train to cruise at top speed for very long or even to reach top speed. But if you're trying to connect to population centres that are speced apart with few or not intermediate stops then higher speed is more beneficial. Therefore, you also need a great enough total distance for the overall time savings to be worth the high cost.
With existing infrastructure, the cost to achieve lower speeds is often so low that it has a more favourable benefit-cost ratio. It's sort of like, the cost to buy a new car instead of a used one at 1/2 the price might seem more appealing if you have no car while the cost to fix up your existing car at 1/2 the cost of used might be a better option that buying either. With rail, a big part of the cost of a totally new rail line is land acquisition which might be totally eliminated if using an existing corridor while upgrading to full HSR means that you'd still have to acquire a lot of land since the corridor would likely have to diverge from its current route to be straighter and more level. There are a lot of HSR routes that started out as conventional routes and were upgraded over time. These tend to have a lower average speed than full HSR, often in the 200-250km/h range rather than the 250-350km/h range but are popular since there is less overall cost or at least less up-front cost.
The general geography is also important since if your route is fairly flat without too many obstacles to either go around or over/under then the cost premium for full HSR won't be nearly as great. Requiring lots of bridges, tunnels, blasting, and other expensive earth-works makes HSR less attractive than a route that can avoid such things by going around them.
Electrification is the other major cost difference since full HSR generally requires it to prove sufficient power to achieve those speeds. Slower lines may or may not be electrified, and if you can get by without electrification then the cost difference between conventional and high speeds is much greater. Slower lines still benefit from electrification if they're very busy meaning there's a great opportunity to save money on the cheaper energy costs or if there's more frequent stops (which are bad for HSR) since you save time with faster acceleration. So for electrification of intercity rail it tends to depend on how busy the route is. So current or projected ridership also helps determine if full HSR cost is warranted.
The most optimal case for full HSR is to connect major population centres of 350-650km with stops no more than every 50-100km. This would mean that they're far enough apart for the high speed to meaningfully reduce travel times while not being so far that air is still much faster.
So to sum up, there is no single optimal speed that applies to all corridors but in Canada it might be 177km/h since that's the threshold that requires many expensive safety upgrades, or it might be somewhere in the 200-250km when a line needs a straighter and flatter route. But under the right conditions, full HSR might be the best option making the pptimal speed in the 300km/h. Beyond that, the trains need to be ever more powerful and ebergy consuming and the equipment more specialized so over 350km/h is rarely optimal. I know "it depends" isn't a very satisfying answer but that's like.
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