O 305 and O 307 establish a new era in bus manufacture

Oct 30, 2008
  • Customers now have a say in design
  • Lifecycle costs become focus of attention
  • Standardization reaches the rural-service bus
At the 1967 Frankfurt International Motor Show, the new O 305 urban bus was presented to the public for the first time; large-scale production began one year later. This ushered in a new era in bus manufacture at Daimler-Benz, with touring coaches and urban buses leading separate lives from then on.
As early as 1966, the designers at Daimler-Benz had submitted the draft of a special urban bus designed for one-man operation and featuring a low floor, high side windows, air suspension, compressed-air brakes and a rear-mounted engine. However, other people had put their heads together elsewhere at roughly the same time and come up with a similar concept: under the management of O.W.O. Schulz, technical director of Hamburger Hochbahn AG, a committee of the Association of Public Transport Companies (VÖV) set out to elaborate recommendations for the standardization of regular-service urban buses – and presented them at the association's annual convention in 1967.
They specified an eleven-meter long bus with rear-mounted engine and a low floor at a convenient height of 725 millimeters. They also suggested double inward-folding doors in front of the front axle and the rear axle, a standardized instrument panel and a central electrics compartment. The rear screen was to be made of a non-dazzling glass and side windows had to be generously dimensioned. And finally, the interior compartment was to provide space for 41 seated and 61 standing passengers.
The members of this committee represented some 70 percent of the German fleet of regular-service urban buses – a powerful argument for the Association’s demands and the reason why the O 305 had to put up with certain modifications shortly before its production startup.
At the time of the launch in 1967, the fathers of the concept would never have thought it possible that more than 16,000 units of the new O 305 urban bus would have come off the assembly lines by the time its career came to an end in 1985. Quite on the contrary, at the 1967 Frankfurt Motor Show, not only the new Mercedes-Benz bus but also its competitors from Büssing and Magirus were critically reviewed. Soon, the mocking reference to the “container on wheels” was passed around. Many contemporary witnesses felt that the new standardized regular-service bus with its rational rectangular shape was too drastic a break with the customary design that dated back to the 1950s and featured familiar elements such as chrome trim and chubby proportions.
But there was method in this apparent madness: the local public transportation operations had come under double pressure even in those days. They had to cut costs and at the same time improve the attractiveness of local public transportation, which was faced with growing competition from the ever more easily affordable passenger car. Passengers were to be attracted by the low floor with convenient entry, by high ride comfort afforded by air suspension and by an unmarred panoramic view through generously dimensioned windows.
Costs had come under scrutiny mainly in three respects: the standardized regular-service urban bus was to cut not only the vehicle purchase price but also the cost of servicing and repairs. Cost-cutting was also at the forefront of the design for one-man operation, whose benefits were, however, initially disputed and bestowed a so-called one-man bonus of twelve percent on many drivers. The director of the public transit authorities of Heilbronn, for instance, drew up a calculation for the district council to prove that the changeover to one-man operation would be an expensive hobby since this would prolong the time the bus spent at stops, with adverse effects on turnaround speeds and an ultimately expensive demand for additional drivers and buses.
This calculation did not work out, as can easily be read off the extraordinarily successful history of the O 305. As early as 1970, the plant presented the prototype of a rural-service bus derived from the O 305, designated O 307, which complied with the local public transportation guidelines for a standardized rural-service bus. The new
O 307 adopted the frame, major parts of the bodywork and the much acclaimed driver's workplace from the O 305 but differed from the latter in that it was 11.7 meters long
(0.7 meters longer than the O 305) and had a 150 millimeter higher floor than the
O 305.
The O 305, which had initially been available with the 8.7 liter six-cylinder OM 360/h engine with either 170 or 192 hp, in its turn inherited the eleven-liter OM 407/h engine, with up to 240 hp, from the O 307 in 1973. From 1973 the O 305 was additionally available with a new three-speed automatic transmission specially developed for the bus by Daimler-Benz and supplied ex factory with or without retarder. This automatic transmission, designated W 3 D 080, was so compact that it was particularly suitable for installation in what was a notoriously small rear-end compartment.
In 1977, the two-axle O 305 regular-service urban bus was joined by a three-axle articulated pusher bus derived from it, the O 305 G which was 17.3 meters long and designed for a gross weight of 26 tons. A very special version of this bus, the
DUO O3 305 G D/E, designed for being alternately operated by electrical energy from overhead lines or by a diesel engine, remained in service in Esslingen in Swabia for many years before it was sold by the town’s local public transit authorities in 1988.
And finally, a fleet of 20 hybrid electric buses – the OE 305 – made a name for themselves by demonstrating the suitability of hybrid electric buses for everyday line service in cities. 13 of these buses did service in Stuttgart, the remaining seven in Wesel in North Rhine-Westphalia. In inner-city operation, these buses operated exclusively on electrical energy supplied by batteries; in the suburbs, by contrast, they operated in the diesel-electric mode, meaning that a low-pollutant and specially encapsulated diesel engine fed the batteries via a generator.
Despite its compliance with the urban bus guidelines defined in 1967, the O 305 was by no means a phenomenon that remained restricted to Germany. In several parts of the world, this bus, of which as many as 4,743 chassis versions were supplied, is still enjoying enormous popularity even today. Singapore, for instance, operated 200 units of the O 305. And as soon as the regulation to procure buses only from Commonwealth countries was abandoned in Hong Kong, the local Kowloon Motor Bus Company ordered an O 305 for testing in 1983. This bus with a 4.5 meter high double-decker body made by Alexander left such a good impression in what was still a British crown colony at the time that another 40 units were ordered – some of these are still in operation today, having made a name for themselves as particularly safe means of transportation. The O 305 buses in the streets of Hong Kong hold a very special record: there has not been a single serious accident with these vehicles in all these years.
From standard urban bus to standard rural-service bus
The drive for modernization which commenced in the mid-1960s was primarily due to the initiative of the transit operators. In addition to being strongly dependent on the satisfaction of their own customers, the passengers, the operators also hoped that the standardization of regular-service buses would produce financial savings, not least because of reduced costs for servicing, maintenance and replacement parts inventories.
But the manufacturers too did not always find it easy to adjust to the new concept, even though they made haste to meet the wishes of their customers. Until then they had all followed their own ideas with respect to dimensions, engines and appointments, and these were not always easy to reconcile with the new requirements.
The market leader Daimler-Benz had just presented the new O 302 model series in 1965. In view of the relatively low volumes for individual segments such as interurban services, the Mannheim plant planned to cater for the entire spectrum of operations, from the urban bus to the comfortable touring coach, with a single model series. However this model was far from meeting the requirements which the Association announced two years later.
Moreover, at the turn of the year 1967/68 a further working group consisting of representatives of the German railway and postal services, as well as associations of passenger transport operators and private sector railways was formed. This working group undertook the task of developing its own guidelines for a standard rural-service bus along the lines of the standard urban service bus. It presented its recommendations in 1969. The following year Daimler-Benz presented a prototype at the “Rail and Road” exhibition in Essen, and series production of the O 307 standard rural-service bus commenced in February 1973.
Demanding specifications
Whereas the O 302 had been designed to cater for both urban and interurban operations, there was to be a major difference between the standard rural-service bus and the urban bus, for in 1967 the VÖV had specified a low floor height for urban buses to make it as easy as possible for passengers to enter and leave the vehicle. The rural-service bus, however, was to have a luggage compartment with a capacity of at least 2.5 cubic meters which could only be accommodated beneath the floor, between the axles. Moreover, with a length of 11.7 meters the rural-service bus was to be slightly longer than the 11-meter VÖV urban bus. Comfortable seat rows were to be provided for roughly half of the 102 passengers. Where the cockpit was concerned the working group followed the lead of the urban bus. The engine output was to be in the region of 200 hp.
It was therefore clear that city and intercity operations could not be combined in a single model series. Nonetheless Daimler-Benz did not miss the opportunity to include its own rationalization efforts in the design concept for the rural-service bus, and made sure that the greatest possible number of O 305 urban bus components were adopted in the O 307, which was presented in 1973. These included not only frame and body components, but also the highly praised, practical and clearly arranged cockpit.
Conversely, the urban bus adopted the 210 hp six-cylinder OM 407h engine from the
O 307 in 1973, replacing the original OM 360h which had an output of only 192 hp. This eleven-liter engine was installed horizontally at the rear, with a 180 hp low-emission variant also available on request. In 1973 Daimler-Benz also introduced a sound-insulated version, the “whispering bus.” To quote a press release: “The engine encapsulation system reduces engine noise to such an extent that the engine of a passing bus can scarcely be heard.”
The O 307 was able to seat 53 passengers in 14 seat rows, with standing room for 48 more. At 879 millimeters the floor level was 150 millimeters higher than in the O 305. The double rear door was 1200 millimeters wide, as in the urban bus, however at the front the O 307 made do with an entry width of 730 millimeters. With a capacity of approx. three cubic meters the luggage compartment even exceeded the requirement of the working group.
Comfort was ensured by air suspension as standard, as in the O 305, while large side windows enhanced the panorama window character. At the front end the two ventilation louvers on both sides of the destination indicator were immediately noticeable. In conjunction with the roof vents, two slim quarterlights in the last pair of windows and a generous heating system, these provided a pleasant interior atmosphere at any time of the year.
The cockpit was practically identical to that of the O 305: a hydraulically damped driver's seat with longitudinal and height adjustment ensured comfortable access to the clearly arranged instruments and controls. Power steering assisted by a steering damper, as well as a turning circle of only 22.3 meters, made slow-speed maneuvers easier in bus stop bays and narrow areas.
Power was transferred to the rear planetary hub reduction axle by either a synchronized five-speed manual transmission or a three-speed automatic transmission. In both cases the gear gradations and the performance characteristics of the engine provided both respectable acceleration and a low level of vibrations at low engine speeds. In fourth gear the speed could be reduced to almost 20 km/h without any significant vibrations occurring.
One thing had changed versus the O 305, however: the prototype of the urban bus had already attracted criticism with its unusual, very deep windshield which curved outward like a sail. Accordingly Daimler-Benz modified the windshield and improved the aerodynamics at the same time. In the O 307 the windshield was also rounded off at the edges, significantly reducing the air resistance to a Cd figure of 0.42.
The requirements of the transit operators for a vehicle with a long operating life and easy maintenance were not only met by the well-proven quality of the engine, the robust suspension and strong body components. The engine compartment and fuel tank, batteries, auxiliary heater and electrical system were also easily accessible via large external maintenance flaps.
In one respect this standardization of urban and rural-service buses did not quite meet the expectations of the transit operators, for although the ongoing costs for servicing and maintenance were significantly reduced, the purchase price increased. Whereas Daimler-Benz had offered the O 302 for DM 65,000 to 88,000 in 1966, the O 307 started at no less than DM 140,000, even rising to DM 290,000 by 1984.
Quality simply has its price, and this was recognized by Daimler-Benz customers. Up to 1984 they ordered 3,985 units of the O 307, making it one of the best-selling rural-service buses of the 1970s. In doing so the customers confirmed the verdict already reached by the specialist world: at the 1973 International Bus Week in Nice the O 307 was immediately awarded the “Grand Prix Louis Bolandard” for technical excellence.
The OE 305 electric hybrid bus was presented in 1978. Its diesel engine drove the electric drive motor via a generator. In terms of performance, this drive system was on a par with that of a diesel-engined O 305 urban bus