Scaling Cleaner Freight Movement

Automatic Engine Start/Stop

Automatic engine start/stop systems start and stop the main diesel engine in an unattended fashion to provide a variety of features without requiring the truck’s engine to idle continuously. These systems have a set of inputs to ensure that it is safe to start the engine without anyone at the controls.

They provide some key features:

There are two different types of automatic engine start/stop systems. The first has a primary goal of maintaining a cab’s interior temperature when the vehicle is occupied. These may also assist with keeping the engine warm and the batteries charged. The second type of automatic engine start/stop system focuses solely on maintaining the batteries’ state of charge.


Little Added Componentry
They do not require additional HVAC components, batteries, or engines to accomplish their tasks.

Can Be Combined with Other Technologies
It is becoming increasingly common to pair an engine start/stop system with a battery HVAC system. This allows the engine to start automatically without driver input when necessary to keep the batteries charged and keep the battery HVAC system from shutting off if it runs low on available power.

Can Avoid Violating Idle Regulations
If a vehicle is purchased with a CARB Clean Idle engine, it will have a serial numbered holographic sticker on the driver’s side of the hood or driver’s door. Such stickers allow automatic engine start/stop systems to be used without violating any idling regulations, provided that the vehicle wasn’t also purchased with the tamper-proof five-minute timer.


Can Interrupt Driver Sleep
Noise and vibration of the system starting and stopping can disturb drivers. Drivers did not like the initial automatic engine start/stop systems that came out about two decades ago because when those systems started and stopped the main engine the noise and vibration was enough to wake a sleeping driver. Newer systems have made improvements, such as using the engine brake to create a more rapid and smooth engine shut-off than the cab rocking and engine sputtering which occurs during a normal engine shut down. If there is a large temperature difference between the desired bunk temperature and the outside temperature, the engine starts can become fairly frequent, exacerbating the sleep interruption problem. Another concern is the alarms that may go off as part of the engine starting process. The system manufacturers offer features to suppress these alarms when the start/stop system is enabled.

Required Main Engine to Idle
Creates additional hours of wear on the main engine.

Issues with Idle Law
It is not completely clear how various idle laws relate to some of the operational modes available with these systems. Refer to the resources listed in section 5.6 for the latest information on idling regulations.

To learn more, download the Idle Reduction Confidence Report.
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