motorways are good ,no steet lighting, so you can leave the shutter open for longer. Just after sunset is favourite you still get some colour in the sky. exposure time as long as you like really. cover the lens when no traffic.
Avoid scenes where sya the cars appear in one spot eg over the top of a hill that spot will overexpose.
Got some niceones from near high Wycombe. The mway comes down a hill then pefroms an s bend on a viaduct and climbs a hill on the other side. I will have to dig them out.