DECAL ROAD (and mesh road) textures must tile vertically. If the case is that your texture only tiles from left to right, rotate the source graphic itself 90 or 270 degrees so that the game can tile it vertically. There's plenty of in-game asphalt textures to use, and failing that you can find stuff on many different sites such as the commercial textures.com or even opengameart.org if you want something free. There's plenty of other sites (both CC0 free-use license and CC-SA license things, and of-course commercial sites exist in numbers), but you must look for them. There's plenty of software out there including GiMP (which is free) which can readily make your texture tile. Asphalt texture like that should be easy to auto-tile inside GiMP. Things like building facades get a little more complicated when trying to tile them, but luckily asphalt is usually pretty easy. Try to find a source file that is rather even in lighting / color, so that it doesn't tile so noticeably even after the graphics program helps it out - otherwise you'll still see it tile, albeit much more smoothly. Good luck!
