Consider a consumer who can choose to travel on a congestible fast mode or
on a congestible slow mode. Users who most value time will use the fast mod
e. A toll on the slow mode can induce some people who initially use that mo
de to switch to the fast mode. A toll on the slow mode with revenue not ret
urned to users then necessarily reduces the welfare of all users. A toll on
the fast mode may raise aggregate consumer surplus.