of driving; the company also introduced two airport coach routes in the same year. 1975 also saw the first overnight routes to be introduced – cross-harbour routes 121 and 122 (now known as routes N121 and N122 respectively), bus-bus interchange was also introduced for the two routes at the toll-plaza of Cross-Harbour Tunnel, the first of such practice in Hong Kong. CMB introduced two suburban coach routes in 1978, using the first model of second generation rear-engined double-decker (MCW Metrobus) in Hong Kong. Early 1980s: Race to the 3-axler, Dragons chasing the Mercedes In the early 1980s, CMB and KMB acquired a number of second-hand buses from UK, but this time all of them were ex-London Transport Daimler/Leyland Fleetlines. In 1980, KMB started to evaluate air-conditioned double-deckers, but the trial was unsuccessful and the air-conditioners of the two buses (one Dennis Jubilant and one Leyland Victory Mark 2) were removed in 1983. In 1981, CMB and KMB introduced the first 12-metre 3-axle double-deckers (MCW Metrobus). Another three 12-metre 3-axle double-decker bus models were introduced in late 1981/early 1982, namely Volvo Ailsa B55, Dennis Dragon/Condor and Leyland Olympian, all except the Volvo Ailsa are second generation rear-engined double-deckers. In 1982, KMB finished the conversion of all of its buses to one-man operation. Following the end of restriction of buying new buses from countries of Commonwealth of Nations, KMB introduced one German-built Mercedes-Benz O305 double-decker in 1983. It was followed by another 40 in 1985. Late 1980s: It's too cool to be in an Olympian, yet cooler in a Falcon In 1985, KMB upgraded its airport coach service by introducing air-conditioned Dennis Falcon, which had the air conditioner driven by the main engine. The service was later named the "Airbus" service. In 1986, KMB introduced the first 11-metre 3-axle double-deckers. These buses were designed with better manoeuvrability than 12-metre buses, with the feature of high capacity retained. KMB resumed the evaluation of air-conditioned double-decker in the late 1980s, unlike those evaluated in the early 1980s, all these buses evaluated had the air-conditioning directly driven by the main engine. In 1987, the trial of one air-conditioned MCW Metrobus was started, but it was unsuccessful and the bus had its air-conditioning removed. Later Leyland Bus delivered one air-conditioned Olympian to KMB and the bus entered service in 1988, it was successful and later KMB started to place orders of air-conditioned Olympians (the prototype Olympian