In more recent times, a number of companies are selling composite railroad ties manufactured from recycled plastic resins, and recycled rubber. Manufacturers claim a service life comparable with wooden ties, and that the ties are impervious to rot and insect attack, and can be modified to provide additional lateral stability while otherwise exhibiting properties similar to their wooden counterparts in terms of damping impact loads and sound absorption. Dimples can be added on the sides and bottom the better to grip the ballast.
Aside from the environmental benefits of using recycled material, plastic ties usually replace timber ties soaked in creosote, the latter being a toxic chemical, and are themselves recyclable. Plastic/Rubber composite ties are used in other rail applications such as underground mining operations.
In 2009, Network Rail announced that they were to begin replacing wooden ties by recycled plastic ones made by I-Plas ltd of Halifax, Yorkshire; but the I-Plas went into insolvency in October 2012.
— from wikipedia.