Time Constraints: The Cost of Sustainability - Sustainable Urban Logistics: Concepts, Methods and Information Systems - page 177

If so, the procedure enters block J-K. This block explores the previous customers
in search for those also located inside the restricted zone. It then readjusts those
customers in the restricted zone to be visited after the time window opens again,
and the ones that are not inside the restricted zone to be visited during the closed
window period, as described in Sect. 3 . If, on the other hand, the time window is
open during the displacement, the procedure simply updates the overall route cost
after the introduction of customer i.
The last calculation determines whether the time horizon has been covered with
the last customer's introduction or because of the readjustment of arrival times due
to their interaction with the time window. If it has, the procedure starts a new route
with a new vehicle, and assigns its first stop to the first customer that could not be
incorporated into the previous route. Otherwise, the procedure moves on to the
next customer, as long as there are customers remaining in the sequence waiting to
be assigned to routes.
Once all the routes have been determined, the fitness value is equal to the sum
of all the route durations plus the sum of the fixed costs associated to the number
of vehicles used.
3 Case Study Application
After calibrating the Genetic Algorithm using a series of specifically designed test
problems, we applied it to a case study analyzing the deliveries of a transport
company operating in the Spanish city of Seville, transporting less-than truckload
deliveries to between 50 and 150 customers daily. Many of these customers are
located inside or near the city center, and the company's operations are greatly
affected by the access time window restriction imposed by the local authorities. In
order to prevent high pollution levels and to avoid their interaction with passenger
flows and with tourists visiting the monuments located there, accessing, or
remaining in, the centre is forbidden for delivery vehicles between 12.00 and 16.00
every day. And, within an intense campaign of pedestrianisation and promotion of
clean transport systems like bicycles, the local authorities are considering to
extend these forbidden hours, and even to extend the restricted area on which the
access time window is applied. But no actions have been taken towards evaluating
the effect of these policies on the costs of transport operators in the city.
Figure 19 shows the distribution of the nodes composing the metropolitan area
of Seville, and which conform the VRPATW graph. When solving the problem,
we assumed that the company could count on a number of vehicles sufficient to
make all the deliveries, and also that the capacity of these vehicles did not impose
any restriction whatsoever on the solutions, corresponding to the real case, where
the company is permanently striving to increase its load factors. We also assumed
a 20 km/h speed for the vehicles, a 20 min unloading time at each customer, and a
time horizon of 10 h, representing the daily operation hours of the company's fleet.
The company's depot is located in one of the industrial areas in the outskirts of the