POINTERS TOWARD THE IMPROVEMENT OF SAFETY IN , DERIVED FROM AN ANALYSIS OF 371 ACCIDENTS INVOLVING BUSES IN AND FROM CRASH TEST RESULTS

F. Alexander Berg INTRODUCTION Walter Niewiihner DEKRA Automobil AG The current official categoriesof road users in Ger- Germany many containsfive types of buses: PaperNumber 9%S4-O-03 - Kraftomnibus (Motor or ) seating more than 9 personsincluding the driver (this category covers all buseswhich can be separatedto ,,Reisebus“(coach), ,,Linienbus“ (public service bus) or ,,Schulbus“ (school bus).

- Reisebus (coach) ABSTRACT - Linienbus (public service bus) DEKRA accident researchdivision has carried out in- depth analyses of 371 accidents involving 395 buses - Schulbus (schoolbus) which occurred from 1985 to 1997 in Germany. From these, pointers were derived toward possible improve- - Oberleitungsomnibus (trolley bus) ments in the active safety and, in conjunction with crash test results, in the passivesafety of buses. Thesedetails have only recently cometo light, as part of an endeavourto be able to show the incidence of acci- With regard to the pre-crash phase of the accidents, dentsinvolving busesseparately within the official traffic findings emerge on, among other things, the relative accident statistics. It has been possible to obtain separate significance and frequency of the following charac- accident figures for coaches, public service buses and teristics: speed being driven before collision, critical schoolbuses from official statistics since 1995. situation triggering the accident (accident type), conse- quencesof bus occupantsand opposites.From these fin- For long-term statistical overviews of total figures dings, potential benefits of technical aids and bus equip- covering accidentsinvolving coachesand buses,the fig- ment can be assessed. ures shown separatelyfor the former German countries are still the most suitable (STATISTICAL OFFICE, A main focus of actual accidentoccurrences involving 1997). Figure 1 showsthe trend in the number of drivers busesconcerns in which busestopple over their side. On and passengersinvolved in accidents who were either this point, relevant characteristics resulting from the seriously injured or killed during the period 1957 to accident assessmentsare also described. The results of 1996. Figure 2 shows the referencefigures coachesand actual accident simulations carried out at the DEKRA busesshown in the official statistics for the former coun- crash centre involving the overturning of a moving bus tries for the sameperiod. onto its side completethis topic. The number of bus passengerswho have been either From the collision parameters (kind of opposite, killed or injured either inside or outside urban areas is driving and collision velocity etc.) pointers emergere- declining over the long-term. However, the number of garding the performanceof appropriatecrash testsfor the bus passengerskilled outside their urban areas has in analysisof internal bus safety.In this context there is also particular been subject to considerable fluctuations in a discussionof the results of bus crash tests carried out at certain years. As can be seenfrom Figure 1 in the former the DEKR4 crash centre (vehicle damage, seat- and countriesthe number of bus passengerskilled outside of passenger-stresses). their local areaper year since the late 60’s, with the ex- ception of 1985 and 1992 has been consistently less than Lastly, using actual accident occurrences,there is a 30. In 1985, 38 bus passengerswere killed, in 1992, the discussionof external bus safety. A description of the re- figure was 35. During the following year, in 1993, three levant characteristicsof collisions with other traffic parti- bus passengerswere killed outside of urban areas. The cipants (, buses, cars, two-wheeled vehicles, pe- reasonsbehind such fluctuations are isolated tragic inci- destrians)provides pointers to potential improvements. dents during which many victims were either injured or killed in a bus involved in an accident. In both 1985 and

791 57 59 61 63 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 I Year 19.. Figure 1. Absolute Frequency of fatal injured or severely injured occupants in buses iu the former German countries within the period 1957 to 1996 (Source: German Federal Ministry of Statistics)

80.000

70.000

60.000

50.000

40.000

30.000

20.000

10.000

0 57 60 63 66 69 72 75 78 81 84 87 90 93 96 Year 19.. Figure 2. Absolute Frequency of registered buses in the former German countries within the period 1957 to 1996 (Source: German Federal Ministry of Statistics) 1992, 20 people were killed in one single accident. If The number of buses registered in the former coun- these two accidents are excluded, the figures for the two tries increased rather steadily from around 30,000 in years do not stand out from the general trend. Such acci- 1957 to approximately 40,000 in 1967. This was followed dents are reported repeatedly and in detail by the media. by an almost linear, significant increase to around 70,000 There is also enormous and lasting public interest in such registeredbuses in 1979. Since that time, the number has incidents. remained fairly constant. Transport performance in kilo-

792 reroplane (private)

Train (passenger)

Aeroplane (line*)

* Line service of 0 500 1.000 1.500 2.000 2.500 3.000 3.501 ICAO-members Traffic volume per fatality [Mio. Pkm / kP] Figure 3. Comparision of the safety of means of transportation (Source: Schesky and Zernick, 1997) metres per person per fatality shows the coach as one of DEKRA database.The vehicle most often colliding with the safest forms of transport, equal to an aircraft flying the bus is the car (57.1% in official statistics, 53 % in scheduledroutes, Figure 3. (SCHESKY and ZERNICK, DEKRA statistics). Individual bus accidents, bus/bus 1997). Correspondingly,the risk of a car passengerbeing accidents and bus/heavy goods vehicle accidents occur killed is approximately 21 times greaterthan the equiva- more frequently within DEKR.4 than in official statistics. lent risk to a coachpassenger. Bus/bicycle and bus/pedestrianaccidents occur less fre- quently in the DEKRA databasethan in official statistics. Nevertheless,improvements to the safety of coaches Accidents which are relatively safe for bus passengers and buses is an important subject, on the one hand to seldomoccur in the DEKRA database. further limit the potential consequencesof isolated coach accidents and on the other, as part of a comprehensive The distribution of accidents over months shown in accident research,to take into account the consequences Figure 5 showsa slightly higher number of bus accidents for the other accidentvehicle. Hence,DEKRA Automobil during the months before and after the main holiday AG has carried out an in-depth analysis of 371 accidents period (July and August). This trend which is recognized involving buses which occurred in Germany between in the official statistics is given even stronger recognition 1985and 1997.The results obtainedfrom real simulated in the DEKRA data. The number of accidentsduring the instrumentedbus crash testsand overturn tests with buses months of May, September,October is significantly dif- supplement the knowledge derived from the accident ferent from the figure for other months. Figure 6 shows a analysis. balanced distribution of the road characteristicsfor bus accidents. A deeper examination of accidents on bends DEKRA DATABASE showed that the number of accidents occmring on left- hand bendsis almost doublethat occurring on right-hand The data sourcesfor the real accident tests are acci- bends. This issue which is discussedin the Report by dent analysis reports produced by DEBRA experts in GIUNDEL and NIBWGHNBR (1995) is to be clarilied Germany.These reports are being evaluatedfor scientific by a correspondingnumber of car/bus collisions. A car purposes in compliance with the Data Protection Act. travelling too fast around a right-hand bend moves onto Figure 4 shows the relative frequencyof individual acci- the wrong side of the road and collides with an on- dents and in the case of accidents involving a second coming bus which from it’s own point of view, is travel- party, the other vehicle concerned,as representedby the ling a left-hand bend. official statistics for road traffic accidentswhere physical injury has occurred (these are accidentswhereby people PRE-CRASH PHASES have been either killed or injured) and for accidentswith seriousdamage to vehicles in Germanyduring 1996.As a Casesof collisions with other road-usersor with fixed comparison, the same diagram shows the corresponding objects,or if the bus overturns autonomouslyare ail gen- frequency distribution for 371 bus accidents in the

793 0 Single Goods Car Two- Pedestrian Other Accident vehicle Wheeler

Figure 4. Single accidents of buses and bus opponents in accidents with two involved parties, com- parison between German federal statistics (1996) and DEKRA database

14

‘;: 12 @ 2 10

s

s 6 2 IA 6 9 'G m 4 z p! 2

0 Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. L J Figure 5. Relative frequency of monthly happened bus accidents, comparison between German federal statistics (1996) and DEKRA database erally precededby the pre-crashphase. If it is possibleto The distribution of accident types in Figure 8 pro- take correctiveaction during this phase,the great poten- vides information on the critical situation precedingbus tial for active safety to avoid the accidentand therefore accidents.W ithin the senseof the official road traffic all its consequencesis exploited. accidentstatistics, the type of accidentis described,“ the conflict situation which resulted in the accident, i.e. a Figure 7 providesinformation on the speedtravelled phasein the traBic situation where the further courseof by the bus during the pre-crashphase in the DEKRA eventscould no longer be controlledbecause of improper examination material. This shows that the majority of action or someother cause”.The most frequent type of busesare travelling at speedsof 91 to 105 km/h preced- bus accidentoccur within the groupof accidentsin lateral ing accidentson motorways.The correspondingspeed on traffic. This group describesthose accidents in which the secondaryroads is between61 and 75 km/h. On local vehiclesinvolved are travelling in either the sameor an roads,the speedis 31 to 45 km/h. opposingdirection.

794 35

g 20

t! L 15

5 -=m 10

0

n=332 Straight Intersection Curve Others

Figure 6. Relative frequency of road characteristics

16

14

E = 10 t &I f P 6 I B A

2

0 stan- l- 16 - 31 - 46 - 61 - 76 - 91 - 106 - over ding 16 30 45 60 76 90 105 120 120 km/h kmih km/h km/h km/h km/h km/h km/h km/h n=264

Figure 7: Relative frequency of driving speed separated to (urban area, outside urban area, motor- way>

The majority of bus drivers involved in accidents FINDINGS FROM THE PRE-CRASH PHASES (78 %) took no evasiveaction before the collision, Fig- ure 9. Almost one of five bus drivers (18 “A) was ableto The behaviourof the driver of a bus has an important initiate at least one evasivemanoeuvre before the colli- influenceon the safetyof its passengers.He should pos- sion occurred.In contrastto the evasivemanoeuvre, three sess appropriatequalifications, start the journey in a of five bus drivers (61 %) applied the brakes,Figure 10. restedcondition and always carry out his functions as a In the majority of thesecases, the brakeswere fully ap- driver in a responsiblemanner. In addition to driving plied. safety, active safety criteria include condition safety, awarenesssafety and operating safety. Bus drivers are subjectto the sameregulations as drivers in respect of rest times.

795 5 - Act. involving stationary vehicles 6 - Ace. between vehicles moving along in carriageway

Figure 8. Relative frequency of accident types

Yes, No Act. Act. Act. after Others w.f.d. swinging despite despite swinging out swinging swinging out

II=173 to the left to the

Figure 9. Relative frequency of swinging out manoeuvres Increasing use is being made of technical equipment Featuresof the active safety of modern busesinclude to support the driver in critical situations and/or in order efficient chassis with lateral acceleration of more than to prevent such situations from occurring at all. Someof 0.6 g to the top limit and brake systems,e.g. with pres- this equipmentwas initially developedfor use on cars and sure operateddisc brakes on the front axle, which on a subsequentlyadapted to the particular requirements of 16 t loadedbus from 100 km/h, facilitate full brake decel- commercial vehicles, hence it is also suitable for buses. eration of 0.7 g, RLECK, 1994). Modem commercial A classic example is the anti-lock braking system AE3S. vehicle brake systemswith high decelerationvalues also The technical equipment currently being fitted maimy have a correspondinguser potential in the bus which is into new cars (e.g. the vehicle dynamicscontrol described shown by the high number of buses(58 “/) which brake by MijLLER et al., 1994, or the brake assistant,KIESE- before accidents. Every meter of distance braked can WETTER et al., 1997) can thereforeprovide pointers for therefore minimize the consequencesof accidents. Cur- other technical improvementsto active safety, the poten- rently, severaltechnical devicesare officially specifiedfor tial of which can be used to further increaseactive bus all buses in Germany, the most important of which are safetyusing information on accidentoccurrence. listed below:

796 / n=313 No braking Partial braking Full braking Braking, w.f.ci. Others

Figure 10. Relative frequency of braking

Single Accident (n=30) Goods vehicle (n=53) Bus (n=l7) Car (n=l2S)

Figure 11. Share of accidents with severe injured or killed bus occupants separated to bus opponents

0 ABVs (automatic anti-lock systems)are specified o Increasedpermanent brake effect for passenger- for all busesand coacheswith a permissibletotal carrying vehicles with more than eight passenger weight of over 12 t which were registeredafter seatsand a total weight in excessof 10 t 1991-09-30(71/320EWG, 8 41 b StVZO). (71/320iEWG/G. App. II).

l Since January 1994,all new buseswith a total In 3.2 % of the cases analysed, it was possible to weight in excessof 10 t, the designedmaximum speed prove that the maximum permissible vehicle speed of of which is over 100 km/h, must be fitted with auto- 100km/h had been exceeded. Therefore, the level of matic speedlimiters. From 1996,even older buses potential usageof speedlimiters in busesshould be cate- (first registration 1988-01-01)have had to be retro- gorized as rather low. Nevertheless,speed limiters can be fitted with automatic speedlimiters. The speedis justified as a preventativemeasure to avoid seriousacci- regulatedat 100km/h (EC Directive 92/6, StVZO dents which could occur when the bus is travelling at a 5 57c, 50. Ausn. Vo. 19 StVR-AVo). signit?cantlyincreased speed. OVERTURN/ROLLOVER - ACCIDENTS further up on the ramp up to the tilt limit, which it reached at a sustained speed of 30 km/h. The bus then From the point of view of passengersafety, individual tilted to the left and skid into the final position, Fig- accidents involving overturn and/or rollover, have a sig- ure 13. nificant meaning. Given the size of the vehicle and the higher seat position, the bus provides a high degree of Five dummies (Dl to D5, Figure 14.) were placed in- protection for its passengersin the event of a collision side the bus. Two of the dummies (D2 and D3, both hy- with most other vehicles (motorcycles, cars, vans). By brid III, 50 % male, instrumented)were restrainedin aisle contrast, the risk to passengersis twice as great if the bus seats by means of two-point belts. An unbelted dummy overturns. If the bus overturns or rolls over, the passen- Dl (also hybrid III, 50 % male, instrumented) sat behind gers not wearing seatbelts will usually fall from the rows dummy D2. As with ECE-R 80, this arrangement was of seatsturned upwards into the danger zone below. Pas- used to examine the potential risk of a belted passenger sengerssitting in this danger zone will then collide with through a passengersat behind without a seatbelt. In this the falling persons and objects which for example escape area, between the two right doors of the bus, the vehicle from luggage racks, and are forced into the impacted side manufacturer retrofitted the seats (shown in Figure 14) of the bus. On this side, the rails, upper and lower win- and the support structures so that they conformed to state dow runs and also the side panes are under extreme pres- of the art in accordancewith ECE-R 80. sure. Should external components from the road and objects located on the road edge (e.g. protective plank The remaining seatsand respective support structures posts) project inside the bus, fatal consequencescan en- were left in their older original condition (year of manu- sue for the passengersdirectly behind this area. facture 1981). The unbelted dummy D4 (Hybrid III, 50 % male, instrumented) was placed in an aisle seat in the From the bus accidents investigated by DEKRA, bus secondrow behind the right door. Dummy D5 which was passengerswere seriously injured or killed in 81 % of also unbelted (Hybrid III, 50 % male, not instrumented) individual accidents(see Figure 11). At 54 %: the risk of sat on the right side of the vehicle in the fifth row, in a being killed or seriously injured in bus/truck accidents window seatbehind the driver. and at 38 % in bus/busaccidents, is essentially lower than in individual bus accidents.Only in 18 % of bus/car acci- dents the bus passengerswere serious injured or killed. This figure of 18 % may initially appear high, given the type of the other vehicle involved. It must be understood however, that after colliding with a car, the bus can be- come unstable and the passengerswill sustain serious injuries as a result of the subsequentcrash.

In order to investigate the dynamics of the passengers and also the impact to the seatsand the supporting struc- tures when a bus overturns, DEKRA performed dynamic tests in the crash centre at Neumtinster. In contrast to the static tests carried out in accordancewith ECE-R 66, in Figure 12. Bus tip over on a ramp the tests carried out by DEKRA in the crash centre, the busesoverturned dynamically on its side. As an example Figure 12 shows a test carried out using a Neoplan N 216 coach. The vehicle was acceleratedby meansof a cable drive from the DEKRA crash centre to a speedof 40 km/h and run with a constant transverse control of the movement over the vehicle’s own system along an optically tracked guide mark with the right front wheel on a ramp. After the vehicle was also run with the right rear axle on the ramp, the traction cable was unhooked. Due to its inertia, the bus continued to run without drive and by means of the transverse control, with the right wheels Figure 13. Bus in final position after tip over

798 In order to obtain more information on facial loadings Dummy Dl Dummy D2 caused by direct contact with the seat or bus structures I(not belted) I (belted) I using the standard options of the instrumented dummies Head injury criterion (Dl to D4) (according to GRGSCH et al., 1990) pres- HIC-36 I 476 I 76 I sure-sensitive film (known as Fuji film) was used, Fig- Resultant head decelera- ure 15. tion 90 !3 45 g (3 ms peak) Also, several acceleration sensorswere fitted to some Resultant chest decelera- of the relevant seat fittings in the bus. To record the ac- tion 7g 6g celeration on the level of the centre of gravity at the front (3 ms peak) of the vehicle, at the vehicle’s centre of gravity and at Resultant pelvis decelera- relevant points on the frame, a total of ten triaxle accel- tion 7g 6g eration sensorunits were installed. (3 ms peak) Femur force The measured values of the instrumented dummies Left/right 1.43 kN I 0.37 ml DltoD4aresummari ‘zed in Table 1. (max.value) 2.14 kN 0.28 kN Belt force The measuredvalues of the belted dummies are sig- (max. value) 2.15 la nificantly lower than those of the unbelted dummies and Dummy D4 Dummy D3 would therefore indicate that the belt reduces passenger (not belted) (belted) injury. Head injury criterion HX-36 20 5 The injury reducing effect of the belt is recorded on Resultant head decelera- high speed film inside the bus whilst it is overturning. As the bus starts to tilt, the unbelted dummies Dl and D4 tion 25 g 7g turn to the left towards the centre aisle. They are - (3 ms peak) rarily restrained by the arm rests on the seats.As the side Resultant chest decelera- of the bus hits the road, the arm rest on the seat of tion llg 7g dummy D4 breaks and the dummy is thrown head-first (3 ms peak) over the opposite seat downwards towards the side win- Resultant pelvis decelera- dow at the point of impact. For any reason, the head tion 14 g 8g remains unaffected from the hard impact, as the head (3 ms peak) decelerates,no increasedvalues are given. As the bus is Belt force overturning, dummy Dl slides against the bending arm (max. value) 1.90 kN rest on its seat, over the centre aisle and its knees take the Table 1. Loadings of the dummies Dl to D4, seating impact of the frame of the seat opposite where it eventu- positions see Figure 14, in a dynamic overturn test ally lands. This collision is characterized by increased thigh forces. When the side of the bus hits the road, Dummy D5 is exposedto an extreme risk of injury from dummy Dl is thrown downwards and the back of its head projecting external parts. hits the luggage rack (increased head deceleration). Also, dummy Dl is thrown against the non-instrumented As the bus is overturning, Dummies D2 and D3 also dummy D5. The consequencebeing that the head and tip towards the centre of the vehicle, their heads, torsos, torso of Dummy D5 is pushed against the side window. arms and legs project into the centre aisle. They are how-

Figure 14. Seating positions of the dummies in the bus

799 ever held in their seatsby the seat belts. This prevents the dummies falling into the highly dangerous areas on the side of the bus taking the impact.

In terms of the results of the film evaluation and the dummy measuredvalues, the evaluations correspond to the pressure film. No increased impact loadings can be ascertainedon belted dummy D3. The unbelted dummy D4 sustainscontact loadings on the chin, noise and fore- head, which is not however categorized as potentially injurious. The damagesustained as a result of the back of the unbelted dummy’s head (Dl) colliding with the lug- gage rack is categorized as potentially injurious in view of the possible skull fracture. Figure 15. Dummy head with applicated pressure Figure 16 shows the bus interior with the dummies in detection foil the end position after the bus has overturned.

FINDINGS FROM OVERTURN TESTS

The tests carried out confirm the known risks to pas- sengers arising from real accidents where the bus over- turns. Here, two-point seat belts (lap straps) for the rows of seatswhich turn upwards when the bus overturns, have a significant far-reachingprotective effect. Static overturn tests in accordance with ECE-R 66 (RIEBECK and BREITLING, 1997) and numerical simulations (APPEL et al, 1996) also provide similar results. Given the current statusof knowledge, two-point seatbelts offer advantages over the three-point belt (shoulder/lap belt). The particu- lar dynamics with side overturns and rollovers can lead to the torso of the belted passengerbecoming free from the shoulder strap. This causesthe entire belt to become loose and there is also the risk of the passengerbecoming re- leasedby the belt around the hips.

The belts must be integrated into the existing restraint system.This type of seat belt system is already available. Obviously, it is hoped that passengerstravelling in buses with existing seat belts will fasten them, as currently is the casewith air travel.

In the case of the seats located on the side of the bus which impacts the road as it overturns, a two-point belt Figure 16. Final positions of the dummies in cannot prevent the heads, torsos, arms and hands of pas- the bus after tip over sengerscolliding with rails or side windows. On the one hand, the effect of this can be minimized by flexible de- sign and padding. On the other hand, if the side structures away from the side bus structures and the road. This fail, e.g. a window breaks,the risk is greaterwhen the bus means that the risk of injury to the majority of the ex- impacts the road. Three-point belts on the outside seats, posed passengersis further reduced, provided that no could, if the seat belts are tightened with a simulated external parts penetratethe bus when it overturns. rohover and if certain threshold values are exceeded (GR6SCH et al, 1996) hold the passengersin their seats. With the dynamic overturn tests so far carried out in Therefore the possibility is given to hold the passengers the DEKRA crash centre on the ramp, the damageto the

800 bus structure in the area of the side wall columns and also ween buses and cars cause the most serious deformation, the upper and lower window runs is less than that found virtually equally distributed between front and side areas. from the static test according to ECE-R 66 and from Some of this damage is caused by secondary collisions many real accidents. In order to increase the structural (also see Figure 11.). In the case of motorcycles and pe- damage during the dynamic test with lateral movement destrians, most of the damage is sustained at the front components during overturn thereby better adapting to and is caused almost exclusively as a result of direct the “worst case” of the real accident, the ramp should be contact with the other vehicle. elevated. Furthermore, in this type of test, various obsta- cles could be placed on the road. Currently, interest is 85.6 % of buses collide at a max. speed of 60 km/h being shown in confirming whether protective devices (Figure 18.). Collision speedsabove this level occur only (crash barriers) from steel or concrete walls, can be dif- seldom. ferentiated in terms of their aggressivenature, in respect of the overturning bus. The overturn speedsof the examined buses are distri- buted over the full speedrange. There are more overturn FRONTAL CRASHES speedsin the 3 1 to 75 km/h speedrange (Figure 19.).

Essential parameters for describing the seriousnessof A typical accident geometry is the rear of the bus on an accident-related collision and/or simulation of sameas the rear of a moving or stationary utility vehicle. In these part of a test, are the location of the main damage, the cases,there is a considerable risk of death or injury for accident geometry and the collision speeds. The fre- the bus driver and persons seatednear to him. quency distributions illustrated in Figure 17., 18. and 19. provide further information on internal bus safety. In the DEKRA crash centre, two tests involving front collisions with buses have been carried out. In one of the The distribution of major damage areas on the poten- tests, the bus (Bussing, year of manufacture 1975, weight tial other vehicle (Figure 17.), shows that in the case of 10 t) travelling at 40 km/h and 70 % frontal overlap, the individual accident, the major damage is predomi- collided into the rear of a stationary 16 t truck with its nantly sustained in the side areas of the vehicle. In the brakes on, Figure 20. In the other test, the bus (Neoplan case of individual accidents, the explanation lies in the N216, year of manufacture 1981) travelling at 31 km/h at frequent number of overturns. In the case of a collision 30% frontal overlap, colliding with the fixed concrete with a truck, most of the damageis sustainedat the front. barrier at the crash cemre, Figure 21. With this accident group (bus/truck), the causes lie in frontal collisions (front bus/front truck) and rear end collisions (front bus/rear truck). Primary collisions bet-

100 90 80 - 70 i??s 60 f 50 5 40 30 20 10 0 Single Goods Bus (n=l6) Car (n=153) Two- Pedestrian Others Accident vehicle Wheeler (n=12) (n=20) (n=24) (n=48) (n- 15) L Figure 17. Relative frequency of main damaged bus areas separated to the different opponents

801 standing l- 15 IS- 30 31- 45 46- 60 Sl- 75 76-90 91-105 106-120 over120 km/h km/h km/h km/h km/h km/h km/h km/h km/h n=257

Figure 18. Cumulative frequency of bus collision speeds (containing all accident configura- tions)

Turnover speed

l- 16 - 31 - 46 - 61 - 76 - over 15 30 45 60 75 so so km/h km/h km/h km/h km/h km/h km/h

Figure 19. Absolut frequency of the speed when the bus turned over

The lateral deceleration measuredat the total centre mies @I) was restrainedin a seatby a two-point belt (lap of gravity in the buses is illustrated in Figure 22., to- belt) and no seat was located in front. The other dummy gether with the decelerationchannel specified for check- @II) sat unbeltedin a seat in front of which was located ing seatsand restraint systemsin accordancewith ECE- another seat. This arrangement produced a restraining R 80 for skid tests. Due to the very flexible front structure effect of the back rest of the seatin front. of the buses (Deformation path Bussing: approx. 0.8 m, deformation path Neoplan: approx. 1.2 m), the decelera- The damagemeasured on the two dummies is shown tion of the centre of gravity is significantly less than the in Table 2. maximum decelerationsspecified in ECE-R 80 and lasts correspondinglylonger. All measuredloadings of the unbelted dummies DII are greater than the corresponding damage values of the Two hybrid III dummies (50 % male, instrumented) belted dummy DI. Since there is no seat in front of were placed inside the Bussing bus. One of these dum- dummy DI, its head and torso can move forwards freely

802 without impact. The increasedforces in the thighs of the unbelted dummies are typical, these occur on impact with the back rest of the seat in front. This causesslippage in the pelvis of dummy DI which is greater than that of dummy DII restrained by the seat belt. Due to the rela- tively low vehicle deceleration, there is no measured value in the area of the corresponding protection crite- Resultant chest deceleration rion. On collision with the barrier, the Neoplan bus occu- pied by the instrumented dummy Dl (not belted), D2 and D3 (belted) and D4 (not belted) and also the non- instrumented dummy D5 (not belted) as in the dynamic overturn test, Figure 12. Table 3. shows an overview of the damagemeasured on the instrumented dummies. The level of damage is generally low and a long way from injury criteria threshold values. Table 2. Loadings of the dummies Dl and D2, in a bus/truck crash test (Biissing bus frontal to rear end The higher damage values are sustained by the dum- of truck, see Figure 20.). mies’ heads and chests. This correlates with the impact on the back rests of the seatsin front of the dummies. As the high-speed film shows, the heads of the belted dum- mies collide with the holding bar and ashtray as they are restrained at the hips by the seatbelts. l?IIc-36 281 62 Resultant head deceleration The unbelted dummies propel forward with hip and (3 ms peak) 23 g 57 g torso and then the knees, followed by the torsos collide with the backrest of the seat in front. In one of the old Resultant chest deceleration rows of seats, on collision with dummy D4, the seat (3 ms peak) 8g 10 g breaks away. On the new, retrofitted seat, which is dama- Resultant pelvis deceleration ged as a result dummy D2 being restrained by the lap (3 mspeak) 15 g 7g strap and the impact of the unbelted dummy Dl sat be- Femur force hind, only slight deformation to the base of the seat. Left There are clearly further loading reserveshere. The seat (max. value) 0.97 kN 0.93 kN can therefore effectively restrain the passenger sat in it Dummy Dummy and there is no additional risk from the passenger sat D4 behind. (not belted) :&ed) Head iniury criterion The evaluations of the pressure film applied to the I%-36 31 66 dummy heads agree with the collision observed in the Resultant head deceleration film. Especially for those passengerswearing seat belts, (3 ms peak) 31 g 41 g there is a risk of injury from the awkwardly fitted holding Resultant chest deceleration bars and ashtrays, Figure 24. On the right forehead of (3 ms peak) 8g 10 g dummy D3, a pressure of approx. 6.5 N/mm2 occurs on Resultant pelvis deceleration collision with the hard plastic components of the ashtray (3 ms peak) 8g 1 10 g and the holding bar, As with the contact damage on the I right cheeks, such type of damage is not criteria for in- Table 3. Loadings of the dummies Dl to D4, seating jury. In contrast, collision damage with the nose at a positions see Figure 14., in a frontal bus impact pressure of around 13 N/mm2 would suggest a potential (Neoplan) with a rigid barrier. nosefracture.

803 FINDINGS FROM FRONTAL CRASH TESTS

The frontal crash tests carried out confirm that the particularly exposed seatsoccupied by the bus driver and the persons sitting next to him are at increasedrisk as a result of intrusions in the front area of the bus. The flexi- bility of the front structuresof the bus lead to a relatively low level of deceleration in the passengerarea behind. This meansthat belted as well as unbelted passengersare at a relatively low risk of injury.

Especially when there is sufficient room in front of the seatfor the head and torso to move, lap belts can offer Figure 20. Bus in final position after impact to passengersprotection in the event of front collision with rear end of a truck the bus. If the back rests of other seats are positioned in front of the passengers,it must be ensured that no awk- wardly positioned and designed components present an unnecessaryrisk of injury. If the seat is positioned cor- rectly and with the correct shape and padding, the back rest can be designed as part of the restraining system for the passengerssitting behind and so effectively support the restraining effect of the lap belt @ROGER, 1986). The double loading when the passengeris restrained and simultaneous collision with the passengersitting behind can clearly be withstood by the state of the art seats and seatrestraints.

Another technical option for integrating the back rests into the restraining systemof the passengerseated behind Figure 21. Bus in final position after an offset is offered by the airbag. There is however a considerable impact to a rigid barrier cost involved with development and fitting into the rele- vant seatsof the bus. Therefore, fundamental cost/benefit - analysesare necessarybefore any of the measuresde- scribed here are converted.

D Retardation channel according to ECE-R 80 1 Time [ms] 400 Figure 22. Retardation of buses in crash tests in comparison to the retar- dation channel according to ECE-R 80

804 EXTERNAL BUS SAFETY

The numberof people injured and killed in individual accidents and accidents with two participants can be taken from the official road traffic accident statistics. These figures are separatedinto accidents within the urban areas,outside urban areas,and on motorways.For 1996, the figures shown in Figure 22 for accidents in Germany, show the number people in the other vehicle who were either killed or injured.

With the exception of cars and trucks, with all other vehicles involved in accidents with buses, the highest numberof peopleare either killed or injured within urban areas.The motorcyclist and the pedestrianare of particu- lar importance.It is not yet possible to use official statis- tics to differentiatebetween bus and coach.One can how- ever correctly assume,that the other vehicle involved the motorcycle or pedestrianaccidents shown in Figure 4 was usually a bus travelling within urban areas.By the very nature of their intended purpose, buses travel almost exclusively within the inner city area.These buses travel in close proximity to cyclists and pedestrianswhen at bus stopsand also on the road. Therefore,the probability of a Fig 24. Pressure imprints to head of dummy D3 collision with theseun-motorized road users is relatively high. In addition, only public transporthas accessto traf- fic free zones in town and city centres and the un- the road, thereby renderingrear and side protectorsuse- motorized road user movesaround carelessly and without less, not many options exist for avoiding the opponentin paying attention. a collision.

Given these facts, measuresfor the bus for minimi- As a matter of priority, particular attention must be zing the consequencesof collisions with pedestriansand paid to avoiding collisions betweenbuses and pedestrians cyclists appearto have little future. Since the body of the and/or cyclists. In this regard, the direct and indirect of the bus, at the rear and the sides all project onto fields of vision for the bus driver through th windows

Goods vehicle

150 200 250 300 Absolute Frequency

•d Urban •BNon urban (excl. motorways) n On motorways

Figure 23. In accidents with buses killed and severe injured opponents and the mirror is of particular significance. However, REFERENCES further measures can also be considered such as addi- tional mirrors at bus stops, additional cameras or sensors Appel Hermann, Rau Hartmut, Rietz Carsten, Rasen- for detecting persons and objects which are likely to col- ack Wolfgang: Safety Belts in Touring Coaches. Procc. lide with the bus, and also audible warning deviceswhich International IRCOBI Conference on the Biomechanics signal that the bus is about to pull out. of Impacts. Sept. 11-13, 1996 Dublin, Ireland pp. 265 . . . 289. The car is the most common accident opponent of the bus. The number of people either killed or seriously in- Grandel Jiirgen and Mtiller Carl-Friedrich: Die Si- jured in accidents with buses is roughly halved between cherheit von Omnibussen. AT2 Automobiltechnische inside and outside urban areas, Figure 23. In those acci- Zeitschrif? 98 (1996) ), pp. 430 .. . 437. dents occurring outside urban areas,it is assumedthat the Grandel Jtirgen and Niewiihner Walter: Untersu- coach and not a public service bus is the most common chungen zur inneren Sicherheit von Kraftomnibussen. vehicle colliding with the car. FAT-Schriftenreihe Nr. 122, Frankfurt am Main, Mai 1995. In modern buses, measuresare being implemented to protect the front of on-coming vehicles. It is therefore Griisch Lothar, Kassing Lothar, Katz Egon, Stechel possible, to effectively restrain a car on colliding at Joachim and Zeidler Falk: Die Beurteilung der Wirksam- 50 km/h and 50 % frontal overlap by using the deforma- keit von Airbagsystemenmit Hilfe neuer Schutzkriterien. tion structure on the car, so that the car passengerscan Verkehrsunfall und Fahrzeugtechnik, 28 (1990) 9, pp. survive without serious injury, RIECK (1994). 247 . .. 254. Griisch Lothar, Mattes Bernhard Schramm Dieter: CONCLUSIONS Restraint Management and Comprehensive Con- cept. Procc. 3th International Symposium on Sophisti- 1. The long-term trend in the number of passen- cated Car Occupant Safety Systems airbag 2000, gers killed in bus accidents is falling. Karlsmhe, Germany, Nov. 26-27 1996, pp. 16-1 . . . 16- 20. 2. Most bus drivers can perform a braking ma- noeuvre before a collision. Improved braking systems Kruger Hans Joachim: The Development of Coach therefore have a high level of potential. Evasive action Seatsas a Restraint System.Procc. International IRCOBI seldom occurs. Conference on the Biomechanics of Impacts, Sept. 2-4 1986Zurich, Switzerland pp. 177 . .. 188. 3. Accidents involving overturns have a greater Mtiller Armin, Achenberg Wiliiied, Schindler Erich, risk of death and serious injury to passengers. Wohland Thomas and Mohn Frank-Werner: Das neue 4. Accidents between buses and cars can cause FahrsicherheitssystemElectronic Stability Program von injury to passengers,which then occur through a se- Mercedes-Benz.ATZ Automobiltechnische Zeitschrift 96 condary collision of the bus. (1994) 11, pp. 656 .. . 670. 5. Seat belts are advisable. In the event of an Kiesewetter Wolfgang, Klinkner Walter, Reichelt overturn, they prevent passengersbeing thrown into Werner and Steiner Manfred: Der neue Brake Assist von the centre of the bus. Seat belts can reduce the high Mercedes-Benz.ATZ Automobiltechnische Zeitschrift 99 number of those killed and injured in serious acci- (1997) 6, pp. 330 . . . 339. dents. Rieck Gerhard: Aktive und passive Sicherheit des 6. In the case of public service buses, it is impor- neuen MAN FemreisebussesFRH 422. ATZ Automo- tant to avoid collisions inside urban areas with un- biltechnische Zeitschrift 96 (1994) 1, pp. 8 .. . 17. protected road users such as pedestriansand cyclists. ScheskyEgon and Zemick Olaf: Personenbefdrdemng im Entfemungsbereichbis 1000 km: Der Luftverkehr im Vergleich. Intemationales Verkehrswesen (49) 1l/97 pp. 557-561 StatistischesBundesamt (1997): Fachserie 8, Reihe 7, VerkehrsunfUe 1996. Verlag Metzler-Poeschl, .

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