A couple things could be going on. 1st the road you are using might not support cars. A simple config line change (in the road's config) can fix that on your machine. or your car rate is low or off. again this is done in the config for the layout.
most likely it is the 2nd. you mentioned toggleing the car button. this button should be toggled OFF (ei the button turns off cars). then build your route and wait and watch. see if they do appear; some times it takes a bit. you can also go into the layout config and look for the line:
"carrate"
try increasing this number. while you are there check to see if you have any cars listed in the config ( line is "car## KUID:###:###:#").
peter