
To prevent accidents caused by driver fatigue, many countries worldwide have implemented official driving time and working hours regulations for drivers. When using planning tools for transportation management such as the VSR Optimizer, driving time regulations have a significant impact on the planning process. The key challenge when incorporating driving time regulations as constraints into the optimizer is the wide range of regulations and types of constraints that need to be considered.
We provide a new feature that supports a variety of driving time regulations. In contrast to the legacy scheduling constraints, that were used to approximate the impact of driving time regulations on the planning process, the new feature produces schedules that fulfill the legal requirements listed below. In particular, rests and breaks are now scheduled continuously. We provide predefined rulesets for the EU and the US. In addition, a large variety of customized constraints can be generated, allowing full flexibility.
The new feature offers a predefined ruleset for the EU regulations. In the following, we explicitly list the regulations that are supported by the optimizer.
Note that waiting time can be used for breaks if the waiting time slot is known beforehand, i.e., explicitly scheduled.
The legal regulations in the US are called Hours of Service (HOS). The predefined ruleset for the US consists of the following regulations.
Note that, again, waiting time can be used for breaks if the waiting time slot is known beforehand.
Consider the following simple domestic outbound scenario in the US, where a truck starts at the warehouse of a manufacturer and delivers products to three end customers. The first picture below shows a schedule without driving time and working hours constraints, which does not respect the official driving time regulations in the US. The second schedule displays the exact same scenario with the predefined US working hours constraints.
In the following, we explain the schedule in more detail. At the first customer, the driver has already accumulated 8 hours of driving. By HOS-3, a break of at least 30 minutes is required before driving to the second customer. Since the break may be satisfied by any non-driving period of 30 consecutive minutes and the delivery takes 20 minutes, an additional 10-minute break is required. After leaving at the second customer, the driver has already accumulated 10 hours of driving since being on duty. Hence, only 1h of driving is legally allowed until the daily driving time limit (HOS-2) is reached and a night rest of 10 hours is required. After the rest, the driver can finish the tour and deliver the remaining products to the third customer.
Note the significant difference between the two schedules, which underlines the importance of considering driving time and working hours regulations during the planning process.
Besides the predefined rulesets for the EU and US driving regulations, the new feature allows incorporating customized rules. General constraints have in common that they consist of a limit, activities that are restricted after exceeding the limit (limited activity types) and a reset period (e.g., a break or nightly rest) that resets the limit. The limit may either refer to a time interval of fixed length or to a sum of the lengths of specific activities. Depending on this variable interpretation of the limit, we distinguish between two types of constraints, namely interval constraints and capacity constraints.
HOS-1 is a rule where the limit refers to an interval of fixed length (i.e., 14 hours), which starts with the beginning of the first activity on duty. This rule is modeled as interval constraint. The limit in HOS-2 refers to a sum of specific activities (i.e., driving), which is modeled as capacity constraint.
To generate a customized ruleset, multiple interval and capacity constraints can be combined. Rulesets can then be added to the desired vehicles. In particular, it is possible to define different rulesets for different types of vehicles.
Customized interval and capacity constraints allow a wide range of rulesets to be modeled. Below we highlight a few properties of rules that are within the scope of the new feature.
Given the properties listed above the new feature enables modeling country-specific driving time and working hours regulations while providing the flexibility to add additional company-specific requirements.
The Driving Time and Working Hours Feature is available as part of Transportation Management S/4 HANA 2023. From OP2023 FP2 on, the VSR Optimizer also supports split breaks, which are relevant for the EU rules. For more information, see https://help.sap.com/s4hana under Product Assistance -> Enterprise Business Applications -> Supply Chain -> Delivery and Transportation -> Transportation Management (TM) -> Planning -> Scheduling -> Considering Driving Time and Working Hours Constraints. For further technical details we also recommend SAP Note 3231830 - Driving Time and Working Hours Modeling Guide.
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