Companies are now able to make their own informed choice about their trains' front end colour, as long as the right risk assessment is done and all affected parties are involved.
Historically train fronts were required to have a yellow panel in order to make them more visible, a move which came in the 1950s when newer diesel and electric trains were found to be far quieter than steam. However since that time, headlamp technology has improved.
Following changes to standards which came into effect last weekend, it's now up to the companies owning and operating trains to make sure they are sufficiently visible. For new and modified trains, this includes having the right arrangement of headlamps in line with legal requirements.
The new standard describes relevant modern requirements and best practice on audibility and visibility, including where yellow warning panels still need to be used on existing trains. Indeed, the yellow front end is still a must for trains without the new arrangement of headlamps, and the spec for the yellow panel is still provided in the new standard where companies find this to be good practice.