Doug McDonald wrote:

Intentional congestion was tried for a while in one of our
downtowns (we have two, one a mile west of campus, one a mile east)
and not only did not work, it drove business to the corn
fields north of the Interstate. The city fathers just had not realized that
this was the certain result of intentional congestion. They fixed the
congestion by reopening the street they closed, and offering various
incentives for business to relocate back there. This was actually extremely
successful, with a now thriving restaurant-bar-boutique area.

While many cities have recreated a downtown area, albeit with
restaurants, bars, and coffee houses rather than retail stores, the
reason that the stores left was not due to traffic congestion either
intentional or accidental. Retail stores followed their customers out to
the suburbs. As those suburbs aged and newer suburbs were created
further out, they moved again.

Where I live we have two greyfield malls in downtown areas. One is
closed, except that Target and Macy's on each end are open (JC Penney is
closed). They will tear down the mall except for Target and Macy's and
restore the previous downtown street pattern, and try to fabricate a new
"historic" downtown. One is turning into more of a restaurant and
entertainment facility, with movies, bowling, and restauarants, and
though Sears, Penney's and Macy's will probably stay there are almost no
retail stores left. They'd have been better off tearing down the
decaying hulk and starting over, but they are trying to cobble something
together, including a movie theater on stilts over the mall structure.

The
big volume business remains where it moved to, with natural congestion,
but certainly adequate roads and very adequate parking.

Your error is in thinking that the big volume business moved out of the
downtown area simply because of traffic.