Game and gamification elements are increasingly seeing use as part of interface designs for applications seeking to engage and retain users whilst transferring information. This paper presents an evaluation of a game-based approach seeking to improve the road safety behaviour amongst children aged 9-15 within the UK, made available outside of a classroom context as an online, browser-based, free-toplay game. The paper reports on data for 99,683 players over 315,882 discrete logins, supplemented by results from a nationally-representative survey of children at UK schools (n=1,108), an incentivized survey of the player-base (n=1,028), and qualitative data obtained through a series of one-to-one interviews aged 9-14 (n=28). Analysis demonstrates the reach of the game to its target demographic, with 88.13% of players within the UK. A 3.94 male/female ratio was observed amongst players surveyed, with an age distribution across the target range of 9-15. Noting mean and median playtimes of 93 and 31 minutes (n=99,683), it is suggested such an approach to user engagement and retention can surpass typical contact times obtained through other forms of web-based content. The size of the player-base attracted to the game and players' qualitative feedback demonstrates the potential for serious games deployed on a national scale.