How do you reduce network congestion?

There are several ways to reduce network congestion. Subnetting and adding routers will break up broadcast domains and traffic. Adding VLANs will do the same while adding security. Upgrading the speed of NICs and wiring, i.e. moving from 10BaseT to 100 or 1000, will reduce congerstion as will moving from half duplex transmissions to full duplex transmissions.