to have your sims commute to other cites you
have to make sure that the roads connecting to your other cities are med dense to high
also make sure one of your town halls has a transportation add on moduel and each city has to have a connection to a train or bus
it takes about 30 mins to see the affects take place *in each city* (so you going to have to play 30 mins for each city you want to see this change to)
also this is very important if one of the cities has enough jobs your sims will not leave your city to commute to an industrial city to find a job
so make sure that if you have two cities that have industrial but your main city has none but has commercial you must remove half the work force
and you will see that sims will have no choice but to leave your current city to travel to another to find a job
so step by step
one make sure city one has no jobs for sims to work for
two make sure roads connecting to the main outlet road are med density
three make sure you have a department of transportation set and bus station and stops all around and or train station
make sure your other cities have bus stations and stops to job sites
and you should see progress in 10 mins or more
i have three cities two are industrial and one is just plain residential
my resident city has all the schools and my other two cities have ppl pouring in to come to school in my resident city
cause i have the only school in the region catch is plop school bus stops in the cities with no schools and the other will pick up the slack
it goes the same for any other zone
my industrial cities have ppl pouring in from my residential city for work cause i have no source of jobs in residential city
hope this works out for yall