Sunken Higway Walls This little set is designed to enhance the look of sunken higways. It provides straight walls that fit on the slopes surrounding sunken ground higways. And it also contains special pieces to nicely integrate overpasses into your sunken higway network. You can find them in the parks menu. I recommend using the hole digging lot for ground higway to get the right slopes beside your higway, especially to get the terrain needed for the onramp pieces. To get them right you should dig a hole with the diggin lot then level the terrain by placing single street tiles. When done lay the highway and plop the overpass, hopefully you should get the right terrain. If not try playin arround a bit with the terrain tools somtimes its just tricky to get it right but in most cases it works fine.