Gave the map editor a try, and maybe encountered a few bugs and/or unintended features:
* Zebra crossing road doesn't duplicate with ctrl + D (but other things do so just fine).
* Zombies walk through certain cars (police car and yellow pickup).
* Used a combination of different roads all placed at the same y level (-0,1), but when transitioning from walking on a road with center marking ( - - - - ) to walking on a plain road it moves the player down a little, even though it appears level.
* Placing more spawners seems to increase wave size or spawn rate?
* At the start of a custom level, it looks like the player doesn't start at the player start position, but is moved there after the first second or two.