Loading and unloading constraints in route planning

In route planning, it is not enough to know where customers are and which vehicle is available.

Each delivery or collection may have specific conditions that directly affect the route: weight, volume, type of goods, loading schedule, unloading time, need for a loading bay, access restrictions or compatibility with particular vehicles.

These conditions are known as loading and unloading constraints.

Taking them into account is essential for generating routes that not only look efficient on a map, but can also be carried out correctly in the real operation.

What are loading constraints?

Loading constraints are the conditions that affect how goods are assigned to vehicles.

The most common are:

• Maximum weight.
• Maximum volume.
• Number of packages or pallets.
• Type of product.
• Compatibility between goods.
• Need for temperature control.
• Loading order.
• Vehicle limitations.

For example, a vehicle may have sufficient capacity by weight but not by volume. Or it may accept certain products but not others. Two types of goods may also be unsuitable for transport together.

If these constraints are not considered from the outset, the route may be unfeasible even if it appears correct in terms of distance and schedule.

What are unloading constraints?

Unloading constraints affect how, when and where a delivery can be made.

Examples include:

• Receiving hours.
• Estimated unloading time.
• Need for a loading bay.
• Access for large vehicles.
• Urban restrictions.
• Staff available at the destination.
• Preferred unloading order.
• Required documentation.

A customer may be geographically close but difficult to serve if it only receives goods during a specific period or requires a vehicle with particular characteristics.

For this reason, unloading must also form part of the planning process rather than being treated as a later detail.

Why they have such a major effect on routes

Loading and unloading constraints determine how orders are assigned to vehicles and the order of stops.

• A heavy order may reduce the capacity available for the rest of the route.
• A long unloading operation may reduce the number of deliveries possible during the day.
• A customer with restricted access may rule out certain vehicles.
• A late loading time may delay the entire route.
• Product incompatibility may require orders to be separated.

Each constraint reduces the number of possible combinations.

This is why real logistics planning is far more complex than arranging points on a map.

Capacity: weight, volume and units

One of the most common mistakes is considering only one type of capacity.

In practice, a vehicle may have several limitations at the same time.

It may have a maximum authorised weight, available volume, a limited number of pallet spaces or a specific capacity for certain types of load.

A route may be valid by weight but not by volume. Or the load may fit by volume but exceed the permitted weight.

For this reason, a planning system must be able to work with different capacity dimensions.

This enables orders to be assigned more realistically and prevents routes that cannot later be loaded physically.

Compatibility between orders and vehicles

Not every order can travel in every vehicle.

Some products may require refrigeration, a tail lift, a closed body, a small vehicle for urban access or special transport conditions.

There may also be customers that only accept certain vehicle types because of access or unloading limitations.

These compatibility rules must be incorporated into planning.

If they are ignored, the result may be a route that appears efficient but cannot be executed.

A good optimisation system must know which vehicles can handle each order and discard invalid combinations.

Loading order also matters

In some operations, it is not only what is loaded that matters, but also the order in which it is loaded.

If deliveries must be made in a particular sequence, goods may need to be loaded so that they are accessible at the right time.

This is especially important when reorganising the load during the route is difficult.

A poor sequence can cause lost time, unnecessary handling or even prevent correct unloading.

For this reason, route planning and load preparation should be coordinated.

Loading and unloading times

Loading and unloading times have a direct impact on route duration.

Two deliveries over the same distance can have very different costs if one takes five minutes and the other forty.

These times affect:

• Total working-day duration.
• Compliance with time windows.
• Number of orders a vehicle can complete.
• Cost per delivery.
• Risk of accumulated delays.

Planning without taking these times into account can create overly optimistic routes.

By contrast, using realistic times makes it possible to build more reliable plans.

Constraints at the point of origin

Constraints do not only occur at the final customer.

They may also exist at the loading point.

A warehouse may have specific dispatch hours, limited loading bays, preparation shifts, variable loading times or restrictions for certain vehicles.

If several vehicles need to load at the same time and the warehouse lacks sufficient capacity, waiting times may arise before the route has even started.

For this reason, in complex operations, planning must consider constraints at both the origin and the destination.

Urban and access restrictions

In urban distribution, access restrictions are becoming increasingly important.

Some areas restrict vehicle entry by size, weight, emissions or time of day. There may also be narrow streets, pedestrian zones, loading and unloading restrictions or difficulty finding parking.

These conditions may require specific vehicles or changes to delivery schedules and sequences.

A route that appears optimal by distance may be unfeasible if it passes through areas the vehicle cannot access.

How route optimisation helps

Route optimisation makes it possible to consider all these constraints together.

The system does not only calculate which customers are close to one another, but which combinations are genuinely possible.

It can decide which vehicle should handle each order, the order in which stops should be made and which constraints are met or breached in each alternative.

It can also compare different scenarios:

• Use more vehicles to comply with constraints.
• Change the delivery sequence.
• Separate incompatible orders.
• Assign specific vehicles to particular customers.
• Reduce waiting during loading or unloading.
• Balance capacity and schedules.

The objective is not to create an attractive route on a map, but an executable plan.

Benefits of considering these constraints

Incorporating loading and unloading constraints into planning provides clear benefits:

• Fewer unfeasible routes.
• Better vehicle utilisation.
• Fewer loading and unloading incidents.
• Reduced idle time.
• Better on-time performance.
• Less operational improvisation.
• Greater control over costs.
• More realistic plans.

When these constraints are ignored, problems emerge during execution. When they are integrated from the outset, the operation becomes more stable.

Conclusion

Loading and unloading constraints are an essential part of logistics planning.

Weight, volume, compatibility, schedules, service times, access, loading order and unloading conditions can completely change whether a route is feasible.

For this reason, good optimisation should not be limited to reducing mileage. It must build routes that can be loaded, driven, unloaded and completed under real operating conditions.

LOGISPLAN applies Evolution Algorithms' experience in logistics optimisation to transform constraints relating to loading, unloading, vehicles and orders into feasible and efficient transport plans.