As I recall -

Canada had already required ditch lights for several years. UP had some SD40-2 that had Canadian horns, ditch lights and dual "blue cards" so they could run through. The US legislation for auxiliary crossing lights adopting the Canadian idea was the prompted by a grade crossing accident that killed several teenagers. Initially, the BN tin can strobes (just about worthless in my opinion) and gyralights/mars lights were to be grandfathered in as being compliant with the rule. As stated, the maintenance on the motors and also initial cost were the primary reasons the gyralights/mars lights faded into disuse. I believe one of the brand names of the fixed position lights that alternated and were aimed at different angles was Oscitrol (sp?), ICG was the biggest user.

The first "factory" equipped SP unit with ditch lights was SSW 7274, a GP40M-2 (GP40 rebuilt to Dash 2 standards by M-K). (I worked there at the time.) SP repair forces quickly learned that a standard 32 volt headlight bulb only worked as a flash cube in place of a 75 volt ditch light bulb. These also had the yellow electronic beacons left inherited from the failed SPSF merger which I never found to be of much use except at night at low speeds they are clearly noticeable approaching a grade crossing. Subsequent orders of "new" SP locos had ditch lights installed by the factory.

I did see one or two SP/DRGW units with ditch lights and gyralights, also some KCS units - you couldn't miss them! The Alaska GP49s also had both.

There is no requirement that the ditch lights flash. Unfortunately, somebody thought this was a good idea. Several manufacturers make the electronic flashing units. The biggest question, especially on retrofitted units, is what triggers them. I've seen them wired so that the ditch lights flash on the front while the bell is ringing even if the locomotive is going backwards or the headlight is dimmed. I consider it to be real stupid for the ditch lights to come on while switching potentially in the face of the poor ground person. (The BN strobes were wired into the speedometer and only triggered at speeds above 5 mph?)At night, I like the ditch lights, but the flashing soon drives you crazy.

You have to admit - the triangular light pattern between the headlight and ditch lights does make it distinctively a train, but there will always be those fools who intentionally or unintentionally end up in front of a train. (I hate any news headline of "Train hits car/truck/person" making it sound like the train went out of its way to hit them and could have stopped short.)