In this tutorial you will see how to easily create a moving locomotive and wagons along the spline track in Unity3D.
Here is the package used in this tutorial: https://drive.google.com/open?id=175cmMzZdrg31spk13ZaCWbaXOt5-h9-c
Please note that this package and scripts are downloded from https://catlikecoding.com (a good Unity tutorials website) and I modified some files.
For security reason I cannot upload a file with .unitypackage extension to my website, so I compressed it int a zip file. You need to extract it before importing to Unity.