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Author's profile photo Marilena Leichter

New Feature: Driving Time and Working Hours Constraints in VSR Optimizer

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. We provide predefined rulesets for the EU and the US. In addition, a large variety of customized constraints can be generated, allowing full flexibility.

Predefined Constraints for EU Regulations

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.

  • EU-1 (Daily Rest): Within each period of 24 hours after the end of the previous daily rest period a driver shall have taken a new daily rest period of at least 11 hours. A ‘rest’ is any uninterrupted period during which a driver may freely dispose of his or her time.
  • EU-2 (9h Driving Time): The accumulated driving time between two rests of 11 hours shall not exceed 9 hours.
  • EU-3 (4.5h Driving Time): After a driving period of 4.5 hours a driver shall take an uninterrupted break of not less than 45 minutes unless he takes a rest period. A ‘break’ is any period during which a driver may not carry out any driving or any other work and which is used exclusively for recuperation.
  • EU-4 (6h Work Time): The driver needs to take a break of at least 30 min after at most 6 hours work time (not only driving time).

Note that waiting time can be used for breaks if the waiting time slot is known beforehand, i.e., explicitly scheduled.

Predefined Constraints for US Regulations

The legal regulations in the US are called Hours of Service (HOS). The predefined ruleset for the US consists of the following regulations.

  • HOS-1 (Daily On-Duty Limit): A truck driver may not drive beyond the 14th consecutive hour after coming on duty, following 10 consecutive hours off duty. Off-duty time does not extend the 14-hour period.
  • HOS-2 (11h Driving Time): The accumulated driving time between two rests of 10 hours shall not exceed 11 hours.
  • HOS-3 (8h Driving Time): Drivers must take a 30-minute break when they have driven for a period of 8 cumulative hours without at least a 30-minute interruption. The break may be satisfied by any non-driving period of 30 consecutive minutes (i.e., on-duty not driving, off-duty or any combination taken consecutively).

Note that, again, waiting time can be used for breaks if the waiting time slot is known beforehand.

Extended Example: US Regulations

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.

Comparison%20of%20two%20schedules%20with%20and%20without%20Driving%20Time%20and%20Working%20Hours%20Constraints

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.

Customized Constraints

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.

Example: Interval vs. Capacity Constraint

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.

Properties of Rulesets Supported by the New Feature

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.

  • Rules where the limit refers to an interval of fixed length.
    Example: A driver must take a night rest after 13 hours.
  • Rules where the limit only refers to a subset of activities.
    Example: The daily driving time is limited to 11 hours.
  • Rules where the start of the constraint can be customized through activity types. Note that they must include all activity types that are limited by the constraint but may include additional activity types.
    Example: A driver may work at most 11 hours after coming on duty.
  • Rules where only a subset of activities is restricted after exceeding the limit.
    Example: A truck driver may not drive beyond the 14th consecutive hour after coming on duty.
  • Rules with multiple reset types. That is, rules where reset periods such as breaks do not necessarily have to be idle time but may also be fulfilled by other activity types (e.g., non-driving activities). A combination of multiple consecutive activities is also valid.
    Example: Drivers must take a 30-minute break after 8 consecutive hours of driving. The break is satisfied by any non-driving period of 30 consecutive minutes.

 

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.

Next Steps: Modeling Driving Time and Working Hours Constraints

The Driving Time and Working Hours Feature is available as part of the SCM Optimizer 14.0 from support patch 21.07.2022 on. The predefined rulesets for the EU and US can be used through expert parameter modeling. Customized constraints are defined via BAdI, requiring TM OP2022 or newer. For further technical details we recommend SAP Note 3231830 – Driving Time and Working Hours Modeling Guide.

 

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