Context: Additionally, there are issues of connections between different electrical services, particularly connecting intercity lines with sections electrified for commuter traffic, but also between commuter lines built to different standards. This can cause electrification of certain connections to be very expensive simply because of the implications on the sections it is connecting. Many lines have come to be overlaid with multiple electrification standards for different trains to avoid having to replace the existing rolling stock on those lines. Obviously, this requires that the economics of a particular connection must be more compelling and this has prevented complete electrification of many lines. In a few cases, there are diesel trains running along completely electrified routes and this can be due to incompatibility of electrification standards along the route.

Question: What is the other issue that comes to sight when using electrification system?
Answer: connections between different electrical services

Question: Why the commuter lines built to different standards can cause be complicated?
Answer: the implications on the sections it is connecting

Question: What is the solution many lines came up with in order to avoid replacing present rolling stock?
Answer: to be overlaid with multiple electrification standards

Question: Why are disel trains  still used on electrified routes?
Answer: due to incompatibility of electrification standards

Question: What can be very inexpensive?
Answer: Unanswerable

Question: What is often built to the same standards?
Answer: Unanswerable

Question: What trains run along partially electrified routes?
Answer: Unanswerable

Question: What is compatible along the route?
Answer: Unanswerable

Question: How many lines have come to be overlaid with single electrification standards?
Answer: Unanswerable