without the need to be suspended during the COVID-19 circuit breaker. Service NR7 is the first-night bus service to be discontinued, others were suspended from 7 April 2020. In April 2019, SimplyGo, a new payment scheme that allows direct fare payment from bank cards, was introduced. Stroller restraint systems were also retrofitted on all wheelchair-accessible buses from July 2019 onward. In addition, LTA also experimented with assistive technology for commuters with special needs on routes 139 and 141 from January to July 2019. 2020s: Sustainable and accessible buses On 3 April 2020, 10 units of Yutong E12 electric buses debuted on SMRT Buses services 944 and 983, on Tower Transit services 66 and 990, and on Go-Ahead service 15. Then on 29 July 2020, 5 units of BYD K9 electric buses debuted on SBS Transit services 135, 162, and 807, with the rollout of the remaining 15 units completed in December 2020. On 27 October 2020, 10 units of Yutong E12DD double-decker electric buses debuted on SMRT service 983, on Tower Transit service 189, and on Go-Ahead services 83 and 118. On 25 August 2021, ST Engineering-Linkker LM312 which is fitted with 3 doors debuted on SBS Transit Service 38 and 40, on SMRT Buses services 176 and 976. On 5 October 2021, ST Engineering Retrofitted Electric Bus, SG3100M which was once a diesel bus was retrofitted to an electric bus debuted on SMRT Buses Service 176. However, it was taken out of service the next day due to rolling back issues and charging connectivity issues. All the Volvo Super Olympian buses were retired from revenue service on 8 April 2020, with the exception of SBS9889U being in revenue service until 11 November 2020. However, 2 buses have been preserved - 1 in Hong Kong for heritage purposes and the other in a special needs school in Ang Mo Kio, Singapore for practical purposes. A sole Mercedes-Benz O405G (Hispano Habit), TIB1238H which operated under Kranji Depot [KJDEP] has been preserved at Kranji Depot and has been deregistered with the "Off Peak" Number plate which has a Red Plate with White Text. November 2020 marked the last day of operation of non-wheelchair-accessible buses with TIB1242U, a Hispano Habit-bodied Mercedes-Benz O405G on Service 169 being the last non-wheelchair-accessible bus on revenue service. On 1 December 2020, all public buses in Singapore became fully wheelchair-accessible. COVID-19 pandemic When the COVID-19 pandemic first emerged