Total travel costs are minimized when \(n_1 = 13\)
and \(n_2 = 7\), not at the equilibrium
The Answer to the "Motivating" Question:
The equilibrium solution is not optimal from a societal
perspective
An Explanation
Negative Externalities:
A cost incurred by a party who had no control over how
it was created
In This Case:
The private cost (i.e., the travel cost incurred by the
traveler) does not reflect the social cost (i.e., the cost
incurred by other travelers)
An Explanation (cont.)
Getting Started:
Suppose there are 10 vehicles and there is only one route
(route 1)
The cost incurred by each vehicle is
\(t_1(10) \cdot 0.25 = 15 \cdot 0.25 = 3.75\)
and the total cost incurred is \(37.50\)
Consider a Change:
Suppose one more person decides to travel
Continuing the Example:
That person incurs a cost of
\(t_1(11) \cdot 0.25 = 16 \cdot 0.25 = 4.00\)
but the increase in the total cost is
\(44.00 - 37.50 = 6.50\)
So, the private cost to the additional person does not
reflect the societal cost
As a result "too many" vehicles will use the route
Changing Behavior
What Do We Want To Change?
Too many vehicles are using route 1 (i.e., 14 rather than the
socially optimal 13)
Can We Order People/Vehicles Around?
In the two route example, what would happen if we ordered
one vehicle on route 1 to use route 2?
Can We Provide An Incentive?
In the two route example, we could charge a toll on route 1
to make it more expensive and provide an incentive for people/vehicles
to voluntarily change routes
Changing Behavior (cont.)
The Route Costs at the Optimal Solution in the Example:
We want to make route 1 \(5.125 - 4.500 = 0.625\)
more expensive
Overcoming Opposition
Electronic Toll Collection:
Without it, collecting the toll itself can impose costs
Revenue Redistribution:
Return the toll revenues (e.g., tantamount to some
people paying others to change their behvaior)
Disguises:
For example, HOT lanes charge for the "good" choice
Negative Tolls:
Make the "bad" choice more attractive rather then the
"good" choice less attractive (e.g., reduce tolls during the
off-peak rather than raise them during the peak)
Going Beyond Route Choice
Travel Choices:
The decision to travel
The origin of the trip (short run vs. long run)
The destination of the trip (short run vs. long run)
The mode
The route
The departure time
Incentives:
Different incentive mechanisms (e.g., gasoline taxes,
vehicle registration fees, usage fees) may need to be used
to influence differen vehaviors