A lot of misconcetions about RR ties. While cresote is still used in the treatment of RR ties, power poles, etc, it is more commonly used as part of a dual treatment. The other part being borax. NS railroad hasnt laid a 100% cresoted tie since about 2005. While some species of wood worked well with cresote, some hardwood, such as white oak, didnt take cresote verywell and just plain didnt last long in certain areas of the country. About 7 years is/was the adverage life span of a cresote tie. Most ties are not changed out because of rot, but instead of wear caused by the ballast. Also, lateral loads will cause the spikes to wallow out their holes and become loose, no longer being able to hold the rail in place. The railroads do not replace all of the ties in a given mile at the same time. With over 3000 ties per mile, it isnt unusual for a railroad to replace about a 1/3 or less of the total number of ties at any given time. Which ties will be replaced are based on a visual inspection which can be very deceiving and subject to the skill of the inspector. (translated to mean, the dumba$$ that cant do any other job right). There are many reusualbe ties replaced every year. Everytie that is removed from a section of track doesnt go to Lowes or Homedepot for landscaping. The old ties are usually sorted with the good ones going to a low traffic density track somewhere and reused. Pretty much the only thing wrong with them is the spike holes got wallowed out allowing loose gage. Flip it over and drive the spikes in the other side and it good for another 7-8 years.
it is also incorrect to suggest that crossties are made from inferior timbers. The railroads dont like having to spend the money to replace bad cross ties. Ties that are split, cracked, full of knots are very rare in a new crosstie. Structually, a crosstie is just as good a timber as timber you would purchase for any other construction purpose, including building a house. A new cross tie would be stronger than your 6x6 pressure treated pine post. And dont forget the word treated when you are considering your pine post, those preservatives aint exactly enviromentaly safe either.
Wish I had a dollar for every cross tie I have installed$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$,