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Spanish viewpoint on safer buses
Page 49
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by Paul Brockington
• Safety measures that reduce accidents to vehicle and passengers and means of promoting safety by improving the comfort of the driver were reviewed in detail in a paper presented at the recent FISITA Congress in Barcelona. The paper, "Characteristics of a city bus from the safety point of view" was prepared by Mr. Santiago Estrada Saiz, of Empresa Municipal Transport, Madrid. It was one of 52 papers read at the Congress.
Dealing with accident rates relative to vehicle length, Mr. Saiz said that the likelihood of collisions increased in propor tion to the length of the vehicle. Statistics showed that urban buses with a length of 36ft had 1.32 collisions per 100,000km (62,000 miles) whereas the rate was 2.04 collisions in the case of a 44ft articulated bus. Driving on the left of the road was far safer than driving on the right, Mr. Saiz claimed. Typically, the number of collisions per 100,000km was 1.32 if vehicles travelled on the left and 3.17 if they travelled on the right.
Mr. Saiz also reviewed the incidence of accidents to passengers boarding and alight ing from buses relative to step height.
Statistics had shown that the accident rate was 0.1 per 100,000km with buses having a two-step entrance and a lower-step height of 8.4in. The rate was 0.23 per 100,000km if the vehicle had a single step with a height of 9.2in. and a single-step of 11.2in. increased the rate to 0.46 accidents per 100,000km.
Boarding and alighting accidents to passengers could be reduced by having one entrance and two exits. Drivers were fre quently injured because of the effort required to climb up to, or alight from, the driver's scat through a door on the same side as the seat. In the latest buses the driver gained access to his seat through the passengers' door on the opposite side.
After detailing the braking requirements of many types of road vehicle including lorries, Mr. Saiz emphasized that a deceleration rate of more than 0.5g was dangerous for urban buses. For passenger convenience a rate of 0.32g should not be exceeded.
Good driver vision was all important to overall safety. The driver, who should be able to sec the feet of a person standing 6.5ft in front of the bus, therefore needed a windscreen with a lower edge no more than 4.9ft from the ground. The angle between the driver's lines of vision through the extremities of the screen should be not less than 90deg.
A warning was given by Mr. Saiz against the use of urban buses with underfloor engines mounted amidships on account of the fire risk involved. Rear engines were preferable if the engine compartment were protected by a fire-resistant material.
Any sound insulating material should be non-absorbant with regard to engine oil. According to statistics, buses with an underfloor central engine had 0.04 serious fires per lm kilometres (620,000 miles), while the number of fires in the case of front-engined vehicles was negligible.
In a review of factors that increased accidents by causing driver fatigue, Mr. Saiz mentioned that comfort could be improved by providing servo steering and an automatic transmission. Additionally a good ride was of special importance to the driver and tests had been carried out to measure vertical body displacement rates of bus bodies on chassis with conventional springing and with air suspension.
The vehicles were driven at 30 mph over an "average" road surface and the tests showed the superiority of air suspension. With buses having conventional springing the proportion of vertical displacements having an acceleration of more than 0.15g was 65 per cent. Pneumatic suspension reduced the proportion to 20 per cent.
Noise was cited by Mr. Saiz as a major contributory cause of the kind of driver fatigue that resulted in accidents. The exterior noise level of buses powered by engines of up to 200 bhp was limited to 89 dBA, while the maximum noise level of buses of greater power was 92 dBA. A noise level of 2 dBA above these limits was allowed in practice.
Interior noise was equally important and larger municipal undertakings were stipulating maximum noise levels for the saloon.
In addition to reducing the noise of the engine a great deal could be done by attention to the bodywork. The body could be rubber mounted and a sound insulating material or glass fibre could be incorporated in the body shell that would also give therm al insulation.