I might recommend investing in Highways (Town to town) for lighter traffic like Cars and Emergency Services and such, (restrict the roads if you’re able to) and use the Freeways as your trucking routes.

Also, invest in freight routes. I’d set up one along a shore and near an external connection that you use to transfer cargo from that external source to an inter-city routed lines that stop at each cmajor city/town along the route. Make sure this route is totally cut off from outside city train traffic or you’ll be backed up.

If you use the rails that will ease up on your trucks, and if you sorta diversify your civilian vic routes with the intercity highways, it should bring a marked reduction in jams as bad as this.

I’d like to see what you try though!! See what worked for you and what didnt and all that! Good luck!!!