Reaction time, and more specifically delayed reaction, is widely cited as a key contributor to vehicular accidents. Reaction time in relation to the ERB is defined as the time it takes for a motorist to react to an external hazard or stimuli and then carry out the appropriate reaction, or evasive maneuver such as braking when a vehicle in front stops. The feedback offered by an HUD is projected onto the windshield of a vehicle with the aim of integrating outside stimuli and the instrumental feedback; thus removing the need to remove a driver's eyes from the road. Studies of reaction time to hazards in HUD vs HDD designs have found that the average reaction times for HUD are faster. This trend appears to continue across demographics, including both categories of experience level and age.
Speed maintenance is the extent to which a driver maintains a speed and adjusts their speed to suit traffic laws and environmental conditions. The use of HUDs appears to produce better speed maintenance in drivers under experimental conditions when compared to HDDs.

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