The objective of the paper is to estimate UK fleet penetration of stability controlled vehicles, and casualty reduction, particularly for younger drivers. Two models (timeline 2003-2030) were developed for predicting UK fleet ESC penetration, one for Availability of ESC, and one for new car Registrations with ESC. Availability of standard ESC fitment increased from 40-53% from 2006- 2008, whilst new car registrations increased from 20-56% from 2003-2008. EC regulation requires ESC new car penetration by 2014, and the models were modified to reflect this requirement. The models therefore project complete standard fitment in new cars by 2014, and full car stock penetration by 2021. The projections also reveal that another 3 million more new cars purchased without ESC in the interim from 2009 before ESC becomes mandatory in 2014, and these cannot be retro-fitted with ESC so represent a missed opportunity for casualty reduction. ESC casualty reduction was calculated using recent effectiveness values from UK studies based on a case control method and induced exposure. With full fleet penetration in 2021 ESC is projected to prevent 9,587 casualties annually including 382 fatalities, with £764 million savings (compared to no ESC). ESC effectiveness estimates reveal that ESC could be effective in reducing 14% of injury crashes for young drivers. These young drivers commonly drive small used cars with ESC rarely fitted. Since full fleet penetration could take 12 years, faster ESC introduction into smaller cars is needed for casualty reduction amongst younger drivers who represent 30% serious injuries & fatalities. Providing ESC on smaller cars so that younger drivers are protected equates to savings of £227 million and 2,844 casualties annually.