Very true. What we need to do here is gather examples of actually how it is being done across the world.

I dont remember whether I had posted this here earlier but here is an example of exactly what you have said.

“The goal of the Railwaste project was to show the feasibility of crosstie production based on secondary raw materials. The RailWaste R&D consortium has achieved the following results:
Identification of a thermoplastic compound mixture based on mixed plastic waste which is technically capable of serving as a crosstie matrix.
Development and implementation of a pilot scale process for continuous production of mixed plastic waste crosstie.
Production of a set of 2.6m crossties for physical testing purposes.
Mounting and fastening tests were carried out with polymer sleepers, such as drilling, cutting and shaping. The benchmark chosen were wood sleepers. The results were very positive, as the the polymer sleeper may be processed with the same equipment as wood sleepers.”

http://www.moreinspiration.com/article/4563-railway-sleepers-from-plastic-waste?q=Railway%20sleepers

http://www.moreinspiration.com/Image/Large?file=4c1b73f1-3bbf-43eb-836c-6c02d6a5a084.JPG