A polarizing filter will help bring out the sky color. Around here, I'd estimate that just one day per month is very good for train photos. To produce the Old Main Line Tour, I captured several hundred photos, then weeded them down to what you see posted. Each season has it own special qualities. Spring has many bright, crisp, sunny days with comfortable temperatures.
Vegetation often is in flower or has pastel shades.
Summer is good for green backdrops, particularly if you want the trees to hide something ugly in the vicinity. Winter is the only time you can capture snowy scenes, plus it's the time to get shots that are otherwise obscured by deciduous vegetation.