[ARCHIVE ANSWER]
There is no way to place a ratio on something clandestine such as smuggling. All the drug
cops I've heard admit they are catching only of fraction of what gets consumed.
Thousands of loads on 18-wheelers get through for every one that is busted.
It also depends on whom, when, and where the smuggling occurs. Tractor trailers
crossing the border aren't happening as much these days, unless with customs assistance,
which is the most corrupt U.S government agency there is.
Also, tunnels change the frequency of travel and the actual load weight. When one tunnel
is completed, one is discovered – some large enough to drive trucks through. No one
sticks to same method either. They might have 500 people simultaneously crossing, some
from on foot with 100 lbs loads on each person one day and 200 people the next. The
same goes for vehicles.
People don't realize the extent of the smuggling. At any border near any city down south,
you’re looking at hundreds of stash houses holding up to a couple tons each. When your
down there, and in it, a ton is nothing at all. Some guys are doing multiple tons weekly
the way small time dealers sell ounces daily.