A simply crossroads = 2 traffic stoppers, 2 slaves, 1 controller plus traffic lights. Connect an East - West road to the traffic stopper and do the same with the North - South road with the second traffic stopper. Select track and place invisible track from the slave to the stopper, one slave for each stopper. Position the stoppers across each other to give you the crossroad effect. Place traffic lights where you want them.
Select properties of controller and select channel, select routes 2 and phases 2, route 1 red and green, route 2 green and red (leave the spl alone).
Select properties of slave and select the same channel as controller, select route 1 repeat for second slave but select route 2.
You need to remember which slave route you attached to the East - West road stopper.
Select properties of the traffic light that faces the East - West and select the same channel and route as the slave. Repeat with the North - South traffic lights and match the second slave.
For example controller on channel 1
East - west slave Channel 1 route 1
Traffic lights channel 1 route 1
controller on channel 1
North - South slave Channel 1 route 2
Traffic lights channel 1 route 2
Don't put a road spline to near the traffic stopper as cars will over run them.