# Interaction principles
Interactions between a driver and a screen must be simple, non-distracting, and easily interrupted, so the driver's attention can quickly return to the road. This section describes how you can: - [Keep information current and glanceable](https://developers.google.com/cars/design/design-foundations/interaction-principles#keep_information_current_and_glanceable) - [Encourage hands-on driving](https://developers.google.com/cars/design/design-foundations/interaction-principles#encourage_hands-on_driving) - [Prioritize driving tasks](https://developers.google.com/cars/design/design-foundations/interaction-principles#prioritize_driving_tasks) - [Discourage distraction](https://developers.google.com/cars/design/design-foundations/interaction-principles#discourage_distraction) *** ** * ** *** ## Keep information current and glanceable To minimize the time drivers spend looking away from the road, onscreen information needs to be up-to-date and easy to understand at a glance: ### Convey tasks \& states at a glance Drivers need to quickly understand tasks or system states by glancing at the screen. They should be able to read the content within 2 seconds and return their focus to the road. > [!NOTE] > **Rationale:** To minimize the time and mental effort required by glances at the screen, make all communication during driving as clear and efficient as possible. ### Provide quick responses Make sure that system response times after user input -- for example, the time between a tap and the resulting ripple animation -- do not exceed 0.25 seconds. If content takes more than 2 seconds to load, a spinner or similar interface change should indicate that the device is responding. > [!NOTE] > **Rationale:** Meaningful, glanceable changes in the interface help drivers understand that the system registered their input and is working properly. ### Provide timely, accurate driving information Show relevant driving-task information immediately and accurately under normal driving conditions. Display any malfunction or safety status in real time. > [!NOTE] > **Rationale:** Drivers rely on accurate, time-sensitive driving and safety information to navigate properly and avoid hazards. *** ** * ** *** ## Encourage hands-on driving Safe driving requires that drivers keep their hands on the wheel as much as possible: ### Use one-handed gestures No operation should require removal of both hands from the steering wheel. Gestures (such as waving to interact with the system) should require only one hand and should not require any maneuvers that could negatively impact operation of the vehicle. > [!NOTE] > **Rationale:** One hand should always remain on the steering wheel. No tasks should interfere with the driver's ability to control the vehicle and respond quickly to events on the road. ### Allow hands-free speech interface Speech-based communication systems should permit hands-free speaking and listening. Starting, ending, or interrupting a spoken dialog, however, can be done manually. > [!NOTE] > **Rationale:** Reduce visual and manual distraction. Simple voice-driven interfaces make minimal visual and manual demands on the driver and help the driver focus on the road. ### Simplify voice interactions Design multistep voice interactions carefully to minimize driver distraction. > [!NOTE] > **Rationale:** Even hands-free voice interactions require cognitive processing and can reduce attention to road-scanning and other driving tasks. *** ** * ** *** ## Prioritize driving tasks The most important tasks a driver performs are those related to driving -- everything else must be secondary: ### Allow driver to control pace Interaction sequences should be interruptible and resumable at logical points. The driver should control pacing. > [!NOTE] > **Rationale:** Because demands on drivers can be unpredictable, interfaces must allow them to suspend interaction at any point. This way, they can refocus attention on driving without feeling that they must hurry to complete a task. ### Prioritize driving-related tasks Information needed for driving and safe vehicle control (such as navigation directions) should be prioritized over information unrelated to driving (such as media titles). > [!NOTE] > **Rationale:** Information should be prioritized based on its role in supporting driving tasks. ### Consider non-driving content carefully Information unrelated to driving (such as ads, social media content, web page content, books, periodicals, email, and subscription alerts) should be carefully considered to minimize driver distraction. > [!NOTE] > **Rationale:** Non-driving-related information may visually or cognitively distract the driver unless it can be absorbed with a quick glance or easily ignored. ### Prioritize sound \& adjust volume for driving tasks The interface should give priority to audio information that is critical to driving. For example, when navigation directions are being relayed, media volume should be lowered or ducked. In addition, users should always be able to fully adjust the volume down to a muted level. > [!NOTE] > **Rationale:** Drivers need to have the option to turn off all audio sounds if they explicitly choose to do so. If audio is on, driving-related sounds such as navigation directions and alerts should be prioritized over non-driving-related sounds. *** ** * ** *** ## Discourage distraction Avoid pulling the driver's attention away from the road for non-essential reasons: ### Avoid hazardous or distracting activities The system should not allow unnecessary and potentially hazardous activities, such as playing most games, manually surfing the internet, or participating in fitness activities involving unsafe hand or foot maneuvers while driving. > [!NOTE] > **Rationale:** Activities that are likely to deeply engage the driver and critically degrade situational awareness should not be permitted. ### Avoid irrelevant movement Avoid displaying dynamic visual information unrelated to driving, such as videos and auto-scrolling text. Carefully consider the use of animations to ensure they aid the driver's situational understanding. > [!NOTE] > **Rationale:** Videos, animations, and auto-scrolling text can tempt drivers to take their eyes off the road for long periods of time. These types of experiences can disrupt driver control and pace of interaction, because visual information is presented at the system's pacing rather than the driver's.