Brightonian wrote: ↑
Mon Apr 24, 2023 10:31 am
Having lived for most of my life south of the Thames, I tend to think of third rail systems as the natural state of affairs, so have never really understood why people in foreign parts (France, Germany, Northamptonshire etc.) go for these overhead lines which seem to fail a lot more in my anecdotal experience. Or do they?
Just asked ChatGPT which is one better, but got an inconclusive response:
On electrified railways, are failures of overhead lines proportionally more common than failures of third rails?
Someone in the ChatGPT office in Manila wrote:
The answer to this question may depend on various factors such as the design of the electrified railway system, the environmental conditions in which it operates, and the maintenance practices employed. However, in general, failures of overhead lines may be more common than failures of third rails due to the following reasons:
Exposure to environmental conditions: Overhead lines are exposed to environmental conditions such as wind, rain, and snow, which can cause them to become damaged or disconnected. Third rails, on the other hand, are typically located closer to the ground and are less exposed to such conditions.
Greater length: Overhead lines are typically longer than third rails, and therefore have a higher likelihood of experiencing failures due to their length.
Maintenance requirements: Overhead lines require more frequent maintenance than third rails, which can increase the likelihood of failures if maintenance is not conducted regularly.
However, it's worth noting that both overhead lines and third rails can experience failures, and the specific factors that influence their failure rates may vary based on the specific system design and operating conditions.
ChatGPT Mar 23 Version. Free Research Preview. ChatGPT may produce inaccurate information about people, places, or facts.
The main reason that people don't generally build 3rd rail systems is that they are a lot more expensive to build. As well as the actual 3rd rail costing a lot more to lay than wires and gantries, there is also the issue that with 3rd rails running at a much lower voltage, you need much more frequent power transformers, because of the voltage drop-off. And that also varies with the level of service. I recall around about 10-15 years ago, one of the 3rd rail areas having to put in loads more power transformers when they wanted to run heavier, more frequent trains on it, which cost a lot of money. For the same reason, there are also substantially higher losses and hence lower electrical efficiency.
3rd rail systems are sufficiently expensive that whenever there is substantial renewal or upgrade work required to be done, it is always a plausible alternative on cost grounds to abandon it, whether to replace it with OHLE, or - until modern concerns about CO2 - diesel.
Safety is also a bit of an issue, because it is much easier for passengers to get within close proximity of 3rd rails, whether by trespassing or falling off the platform.
The main reason that the railways south of London got 3rd rail was aesthetics. For some historical reason, not affecting the view got a larger consideration in the southern counties.
3rd rails make a bit more sense in underground railways, because it saves on tunnelling costs to avoid boring the tunnels to the clearances needed for OHLE.