Sometimes we have to put equipment in certain positions to ensure drivers both get the right information and that if there is an incident, we know about it automatically.
Occasionally equipment cannot be placed at these positions because of a bridge (for example) or because the cost of the ground works is so high it is not achievable. When this (rarely) happens I have to write a report to our big boss telling him/her why I have chose to put it in another place and the safety implications.
This takes time to come up with another solution that wont cause people harm but does allow us to have the technology required. This is called departing from a standard and it is a time consuming, high word count report.