After doing a bit of research I was unable to find any reference in railroad documents refering to the city of Salem requiring yellow flashing lights (gumballs) on SP's diesels. There was nothing in any SP&S document that mentioned any such regulation since their N-S mainline ran parallel to the SP in downtown Salem. I also checked with a former NP/BN employee that said that knew of no such regulation in Washington state.

At one time the SP did begin putting the gumball lights on SW 1500's but it was not in response to any particular city regulation. It was thought that this program was partly driven by the cost of maintaining the Mars lights that SP so loved.

However, one former SP operating officer did say that yard masters liked the gunball lights. It was easier to see where the engines were located while looking down from the yard tower in a place such as Eugene.

Don't know if this solves any "mystery" about the Salem gumballs.