SAE J1791: Dual Position Driving Controls and Displays for Self-Propelled Sweepers and Scrubbers

Self-propelled sweepers and scrubbers used in industrial and municipal settings often need to be operated from either side of the machine. SAE J1791 (reaffirmed 2022) establishes the requirements for designing, constructing, and ensuring the safety of dual position driving controls and displays for these vehicles. The standard covers both originally built machines with two driving stations and conversions of single-position truck chassis. This article provides an overview of the key technical requirements, design insights, and best practices outlined in the standard.

Understanding the Scope of SAE J1791

SAE J1791 applies to self-propelled, driver-operated sweepers and scrubbers as defined in SAE J2130-1. Its purpose is to ensure that regardless of which driving position is used, the operator has safe and effective control of the machine. The standard defines primary controls (service brake, accelerator, steering, clutch) and secondary controls (parking brake, gear shift, speedometer, displays, lighting, turn indicator, mirrors, wiper, horn). For machines converted from a single driving position, the standard provides recommendations for design, construction, and safety, emphasizing that national regulations take precedence when they exist.

Key Technical Requirements for Dual Position Controls

The standard mandates that all primary controls must be duplicated for both driving positions and function at all times. Exceptions are allowed for duplicated power steering systems and electronic accelerator pedals, where the redundant driving position may be disabled. Secondary controls and displays may remain single if they can be reached and observed naturally from both positions without compromising posture or safety. The following table summarizes the two implementation approaches—slave and duplicated— for primary control systems.

Ergonomic compliance is critical: control layout must meet the reach and seating requirements of SAE J898, SAE J287, SAE J1517, and SAE J680. Mirrors must satisfy SAE J1050 for visibility from both positions.

Design Insights and Best Practices

When converting a single-position chassis, engineers should duplicate primary controls using original equipment components or equivalents to maintain consistent operation and feel. Locking fasteners used in primary control linkages must be replaced with new ones if they are removed during conversion, as reuse could compromise joint security. Slave systems use mechanical linkages to a single master control, while duplicated systems employ independent components for each station. The choice depends on cost, complexity, and space constraints, but both must replicate the original equipment’s control characteristics.

Frequently Asked Questions

When must secondary controls be duplicated?

Secondary controls and displays may be single only if they can be operated and observed from both driving positions without requiring unnatural posture or movement. If the requirements of SAE J898, SAE J287, or SAE J680 are violated for any secondary function, duplication becomes mandatory.

What is the difference between a slave system and a duplicated system?

In a slave system, a single master control (e.g., master cylinder) is shared, with the second driving position using a mechanical linkage actuating the master component. A duplicated system uses separate, fully independent components (e.g., two steering gears) for each position, allowing independent actuation without mechanical interconnection.

Do national regulations override SAE J1791?

Yes. The standard explicitly states that if national regulations specify requirements for driving control systems, those regulations take precedence over the recommendations in this document.

What are the requirements for rearview mirrors?

Any combination of mirror systems is acceptable, but they must meet the field-of-view requirements of SAE J1050 when the machine is operated from either driving position. This often necessitates dual mirrors or adjustable mirrors that maintain compliance from both seats.

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