This involves a train trip my brother took in April 1981 from Tucson, AZ to El Paso, TX.
I am submitting this event in case it correlates with some other report you may have received from the same time and place.
West of a small city in New Mexico which my brother believes is Deming, the train conductor came through the car and instructed everyone on the south side (right side) of the train to pull down the window shades and not to look out the window. My brother pulled down the shade, but peeked behind it. He saw a freeway beside the track (I-10) filled with stopped emergency vehicles – police cars, ambulances, fire trucks. This continued for miles. It was just before noon. The weather was good. The track and freeway are about 35 miles from the Mexican border. The area is quite arid and sparsely populated. My brother stopped in El Paso, TX for 2 days and examined the TV news and newspapers for reports on the incident. There was no information at all – nothing about a freeway closure or the hundreds of emergency vehicles stretched along I-10.
It is unlikely to have involved a nuclear test due to the close proximity to the international border and to Deming.