a positive effect of ridership and revenue levels. Under the Transport Act 1985 the Disabled Persons Transport Advisory Committee (DPTAC) (or commonly DiPTAC) was established to provide independent consultation on accessibility issues. In the same year, the first low floor bus specification was drafted by DPTAC. The Disability Discrimination Act 1995 provided for the completion of the Public Service Vehicles Accessibility Regulations 2000, which specified that all new public service vehicles over 22 seats should be low floor from 31 December 2000, with smaller vehicles mandated from 1 January 2005. The 2000 regulations do not require retro-fitting of pre-existing vehicles or the enforced sale of non-compliant existing vehicles, allowing operators to retain a high floor vehicle until "the end of their economic life". In reality, as the prevalence of low floor buses spreads, combined with grants/incentives, it is likely that the prevalence of high floor vehicles in the national fleet will markedly reduce before all buses were de-registered by 27 October 2014. In the past, in times of reduced economic investment, it was not uncommon for service buses to be used for 15 to 20 years. While some coaches have been produced with a small front low floor section at the driver's level, most coaches in the UK are being made accessible through the use of wheelchair lifts, with the 2005 Caetano Levante being one of the largest introductions. While another widely stated benefit of low floor buses is quicker boarding for able-bodied passengers due to the lack of steps, studies have found the opposite effect in the UK. This is apparently due to the prevailing system of operation where passengers enter and exit through one single front door. It has been suggested that the previous 1980s/90s high floor step entrance buses which featured a centre rail, encouraged a bi-directional flow of entering and exiting passengers simultaneously. The removal of the pole to allow wheelchair/buggy access created the situation where the quintessentially polite British bus passenger would wait for all passengers to alight before boarding, leading to an increase in dwell times. Americas United States In the United States, the Americans with Disabilities Act is credited with motivating the development of low-floor buses, directly affecting the standardized design of the Transbus Program, which concluded with the introduction of so-called 'interim' Advanced Design Buses with a lower floor height but which required lifts to board passengers in wheelchairs. The first low-floor