Route planning with time windows
Route planning with time windows makes it possible to organise deliveries, collections or visits within each customer's available hours. Effective optimisation must balance distance, waiting times, vehicle capacity and operational constraints to build feasible and efficient routes.
In many transport and distribution operations, delivering an order on the scheduled day is not enough.
Often, each customer can only receive goods within a specific time slot. This may be due to staff availability, warehouse opening hours, access restrictions, unloading shifts or commercial agreements.
These time slots are known as time windows.
Route planning with time windows is more complex than planning based solely on distance, because the system must decide not only which vehicle handles each order, but also when it should arrive at each location.
What is a time window?
A time window is the period during which a delivery, collection or visit can take place.
For example:
- One customer may receive deliveries from 8:00 to 10:00.
- Another may only receive them from 12:00 to 14:00.
- A warehouse may allow unloading until 13:00.
- An urban area may restrict access at certain times.
In these cases, arriving too late may cause an incident. But arriving too early is not always a good solution either, because it may lead to waiting.
This is why time windows must be treated as a central part of planning.
Why they make optimisation more difficult
If there were no schedules, many routes could be built by grouping nearby orders and sequencing them by distance.
But once time windows are introduced, the shortest route may no longer be feasible.
A nearby customer may have a later delivery window, while another farther away may require an early delivery. In that case, the vehicle may need to travel farther first and return to a nearby area later.
This may appear less efficient geographically, but it may be necessary to meet service requirements.
Time windows require a balance between distance, time and sequence.
Not all time windows have the same importance
In practice, not all time windows are managed in the same way.
Some are strict. If the vehicle arrives outside that interval, the customer will not accept the delivery.
Others are preferred windows. The customer would rather receive the delivery within a specific period, but may accept some flexibility.
There may also be commercial windows, operational windows, loading-bay schedules, agreed time slots or legal access restrictions.
Distinguishing between mandatory constraints and preferences is important for building a realistic plan.
If everything is treated as an absolute constraint, the system may struggle to find feasible routes. If everything is treated as flexible, the plan may fail to meet important conditions.
The problem of waiting times
Meeting a time window does not necessarily mean that the route has been well optimised.
A vehicle may arrive before the permitted time and have to wait.
That waiting time does not add mileage, but it does consume driver time, vehicle time and the available working day.
If a plan creates a lot of waiting, it may look correct on the map but be inefficient in practice.
This is why a good planning system should try to reduce both delays and unnecessary waiting.
The key is not only to arrive within the window, but to organise the sequence so that the route flows efficiently.
Time windows and vehicle capacity
Time windows cannot be analysed in isolation.
They must also be combined with vehicle capacity.
A vehicle may have enough capacity for several orders in an area, but not enough time to deliver all of them within their windows.
Likewise, a route may be feasible in terms of load but infeasible in terms of schedule.
This shows that logistics planning must solve several decisions at the same time: order allocation, visit sequence, loading, route duration and compliance with schedules.
To solve all these variables together, a transport route planner must take time windows into account from the start of the calculation, rather than treating them as a later check. In this way, it can assign each order to the right vehicle and build sequences that are both efficient and genuinely executable.
Optimising only one of these variables can produce incomplete solutions.
Narrow time windows
Very narrow time windows are particularly difficult.
The smaller the available margin, the less flexibility the system has when sequencing routes.
An order with a fifteen- or thirty-minute window can shape the entire plan for a vehicle. If several orders have narrow windows on the same day, the problem becomes much more delicate.
In these cases, it is advisable to identify the most restrictive orders from the outset.
A good strategy is to build the plan around these critical constraints and then insert more flexible orders into the available gaps.
Penalties for non-compliance
In some scenarios, not all breaches have the same severity.
Arriving five minutes late may be acceptable for some customers, but completely unacceptable for others.
This is why optimisation systems often use penalties.
A penalty assigns a cost to failing to meet a time window. The greater the delay or the more important the customer, the higher the penalty can be.
This helps the system compare alternatives.
A route with fewer miles may miss a critical delivery, while a slightly longer route may meet all important schedules. In that case, the second route may be better from an operational perspective.
Replanning during the working day
Time windows also make it harder to manage changes.
If a vehicle is delayed at one delivery, that delay may affect the rest of the route. A small deviation early in the day can lead to later breaches.
This is why dynamic operations may require replanning.
The system can assess whether it is better to change the order of the next stops, move an order to another vehicle or issue a warning about a risk of non-compliance.
Planning with time windows should not be just a static snapshot at the start of the day. In many operations, it must be able to adapt to what happens during execution.
Benefits of planning time windows effectively
Managing time windows correctly delivers clear benefits:
- Better on-time performance.
- Fewer failed deliveries.
- Less unnecessary waiting.
- Better use of the working day.
- More realistic routes.
- Better customer service.
- Fewer operational incidents.
- Greater control over planning.
When time windows are properly integrated into the optimisation process, the resulting routes are more reliable and executable.
Conclusion
Route planning with time windows requires more than calculating distances.
Each delivery must fit into a sequence, a vehicle, a working day and a specific time interval.
Good planning must balance mileage, schedules, waiting, capacity and operational constraints. Only then is it possible to build routes that are both efficient and feasible in real operations.
In operations with demanding time windows, LOGISPLAN applies the experience of Evolution Algorithms in logistics optimisation to build routes that are not only efficient, but also feasible in practice.