Abstract: Motorcycle braking distance is one of the main components of motorcycle stopping sight distance. Motorcycle braking perfor-mance in different situations was not consistent in published literature. This research measured the riders’ braking distances and decelerationsto both unexpected and expected objects. For braking maneuvers to an expected object, 89 motorcycle riders released the accelerator andapplied the brake as quickly as possible following activation of a light beside the road of both dry and wet pavements. As for an unexpectedobject, 16 nonalerted subjects were confronted with the need to stop for an unexpected object along the roadway. Vehicle speeds, brakingdistances, and average deceleration were computed for each braking maneuver. Results showed that the deceleration varied among the ridersin which 90% of riders’ decelerations were at least 2.75 m=s2 under wet conditions, whereas 90% of all riders decelerated at least 3.3 m=s2
Motorcyclists are often exposed to a higher risk of road accidentscompared with occupants of passenger cars, and so it is verylikely for them to be involved in accidents [National HighwayTraffic Safety Administration (NHTSA) 2007; SafetyNet 2008;Department for Transport 2010]. Hurt et al. (1981) identified thatimproper braking was one of the major factors leading to crashesinvolving motorcyclists. This is also supported by Kasantikul(2002) and an in-depth study on motorcycle accidents in Europe(Manufacturers 2004). Motorcycles are also more likely to beinvolved in a collision with a fixed object compared with othertypes of vehicles. The National Highway Traffic Safety Adminis-tration (NHTSA 2007) stated that more than 28% of road injuriesinvolving motorcyclists were caused by collisions with fixedobjects.
Apart from that, exclusive motorcycle lanes were introduced inMalaysia as one of the engineering measures designed to minimizemotorcycle accidents and injuries to motorcycle riders. It wasproven to be effective, even though proper design guidelines werestill not available during that time (Tung et al. 2008). In designingthe motorcycle lanes, provision of required motorcycle stoppingsight distances at every point along the path, such as along hori-zontal and vertical curves, is essential (Davoodi et al. 2011).
One of the most important components in motorcycle stoppingsight distance is motorcycle deceleration rate (braking distance).Unfortunately, the motorcycle lanes in Malaysia were designedaccording to cycle tracks, and do not take into account the behaviorof riders and their motorcycle characteristics that may lead toaccidents along the lanes.
Braking performance is a critical skill for motorcyclists to avoidinjury, and safe braking is very important to improve their safety.The operation of brakes on most motorcycles is much more com-plicated than on passenger cars (Teoh 2009). Most motorcycleshave separate controls for the front and rear brakes: the front brakeis usually controlled by a lever on the right handlebar and the rearbrake is controlled by a pedal operated by the rider’s right foot.In contrast, a passenger car generally has a single control, wherethe speed is reduced by pushing the brake pedal with the driver’sright foot.
The current design standard of AASHTO (2011) specified avalue of 3.4 m=s2 for deceleration using a passenger car as thedesign vehicle. This value was based on a study by Fambro et al.(2000) that reported about 90% of the drivers chose decelerationsgreater than 3.4 m=s2. These decelerations were within drivers’capability to stay within their lane and maintain steering controlduring the braking maneuver on wet surfaces. The Institute ofTransportation Engineers’ (ITE) (2008) Traffic Engineering Hand-book stated that decelerations up to 3.0 m=s2 are reasonably com-fortable for passenger car occupants.
Deceleration Rate
With enough pressure, the brake must be applied to stop the vehiclein a braking situation after being signaled. John El and Antoine(2007) defined deceleration rate as mainly influenced by the ve-hicle’s braking performance and the driver’s foot action againstthe brake pedal, which is different for every individual.
1Dept. of Civil Engineering, Faculty of Engineering, Golestan Univ.,Gorgan, Iran (corresponding author). E-mail: [email protected]
2Dept. of Civil Engineering, Faculty of Engineering, Univ. of PutraMalaysia, 43400 Serdang, Selangor, Malaysia.
The deceleration rate in response to braking was quantified throughsimulator and test-track studies. Mazzae et al. (2000) reported theuse of the Iowa Driving Simulator during intersection-incursionscenarios to examine the effects of the antilock braking system(ABS) against other factors such as conventional brakes, ABSinstruction, speed limit, and time-to-intersection (TTI) towardsthe crash avoidance performance and the driver’s attitude.
Averages of 0.8 and 0.65 g of deceleration were recorded forsimulator and test-track studies, respectively. Maximum decelera-tion of 0.9 g and an average of 0.42 g were documented whenthe participants were instructed to make a sudden brake duringa study of lead-vehicle deceleration on a test track (Kiefer et al.1999). An average median deceleration of 0.27 g was obtainedfrom a test-track study involving lead-vehicle-moving, whereas0.37 g was obtained for a lead-vehicle-stationary scenario (Smithet al. 2003).
Fambro et al. (2000) studied the variations in braking perfor-mance to determine stopping sight distance. They distinguishedbetween two cases of braking performance in which, for the firstcase, it was assumed that the driver was surprised by the action,whereas in the second case, the driver was already expecting thebraking. Their research showed that most passenger car driverschose decelerations greater than 5.6 m=s2 when confronted withthe need to stop for an unexpected object along the roadway.On wet pavements without ABS, 90% of the passenger car driversproduced a deceleration rate of at least 3.4 m=s2. These decelera-tions were within drivers’ capability to stay within their lane andmaintain steering control during the braking maneuvering on wetsurfaces. The mean deceleration for all drivers was 0.6 g with astandard deviation of 0.19 g. In this research, a normal distributionwas used, because only the mean and the standard deviation wereknown. The normal distribution was truncated by a minimum andmaximum value of 0.25 and 0.8 g, respectively. Fancher andGillespie (1997) noted that braking distances for passenger carsand trucks differed on dry pavement but were nearly the same onwet pavements. A review of braking distances by Harwood et al.(2003) indicates that trucks equipped with antilock brakes canachieve deceleration rates in controlled braking nearly equal to therate used by passenger car drivers as stated in AASHTO guidelines.
Motorcycles
Ecker et al. (2001) investigated perception response time (PRT) us-ing an instrumented motorcycle in a training facility. Straight-roadbraking maneuvering under dry road conditions starting fromapproximately 60 km=h until full stop was achieved. A red signallight was mounted on the instrument panel of the motorcycle andperipherally positioned for visual field of the motorcycle operation.The participants were then assigned to ride at approximately60 km=h along a straight part of the test facility and to make a fullstop emergency braking maneuver when the bright red flare ofthe signal light went on. They measured a mean distance-averageddeceleration 6.19 m=s2 and a standard deviation of 1.20 m=s2.
A field study was conducted by Vavryn and Winkelbauer (2004)on closed test tracks to measure deceleration of motorcycles on drypavement. The braking performance of motorcycle riders has beencompared with the test riders who rode their own motorcyclesand with ABS-equipped motorcycles. The mean value of brakingdeceleration of all riders using their own vehicles was 6.6 m=s2
with a standard deviation of 1.4, whereas the mean value of decel-eration with an ABS motorcycle was 7.8 m=s2 and a standarddeviation of 1.1 m=s2.
Purpose of the Study
Most studies on braking performance focused on passenger carsand trucks rather than on motorcycles. Limited research has beenconducted on motorcycle braking performance and riders deceler-ation in stopping situations. The motorcycle braking distance isan important factor in determining horizontal and vertical curvelengths to provide sufficient stopping sight distance in an exclusivemotorcycle lane. The objectives of this study were to determinethe motorcyclist deceleration under expected and unexpectedobject situations and to eventually recommend suitable motorcy-cle riders’ deceleration for determination of motorcycle stoppingsight distance.
Methodology
The study on the performance of motorcyclists consisted of twoexperiments. The first experiment evaluated riders’ performance inresponse to an expected object, whereas the second experimentevaluated the braking performance of motorcyclists in response toan unexpected object. A successful braking maneuver is definedby the riders’ capability to stay within their lane (direction) andmaintain steering control during the braking maneuver (as assumedby AASHTO). Both studies were conducted on closed courses withparticipants representing the population of riders in Malaysia.
Experiment 1 (Expected Object)
Participants
Participants were recruited from Universiti Putra Malaysia andalso the state of Selangor in Malaysia through newspaper advertise-ments and flyers. Interested riders were screened to ensure theywere licensed motorcycle riders and to see whether they had anyhealth issues that could exclude them from taking part in the study.Eighty-nine motorcycle riders, including 56 males and 33 females,were recruited. Sixty riders (38 males and 22 females) were be-tween 16 years to 30 years old with a mean age of 25.4 years.Twenty-nine riders (18 males and 11 females) were 50 to 60 yearsold with a mean age of 54.7 years.
Equipment
The motorcycle braking experiment was located within the campusof Universiti Putra Malaysia campus, which has an appropriatesetting for the research. The first concern for the test site was safety.The path was flat, level, straight with adequate width, and wasguided by traffic cones similar to exclusive motorcycle lanes inMalaysia. The apparatus used for the test included a main stationto examine the motorcycle braking performance and reference stripmarkers across the roadway surface for use as a scale to measuredata (Fig. 1). The whole system for the rider deceleration ratiomeasurement consisted of the following components:1. Two Sony HDR-XR 520 and one Samsung HMX 20C cam-
corders set up according to the following criteria (Fig. 1):(1) the entire motorcycle is captured, (2) the participant is seenin the video, and (3) the light is captured as the detection mark.This type of Sony camcorder can record at variable time-lapserates of 240 frames per second and has a large hard disk driveof 240 GB. The Samsung camcorder can also record at vari-able time-lapse rates of 300 frames per second.
2. Three adjustable tripods to facilitate a flexible camera orienta-tion setup.
3. Orange cones situated along the experiment site to specifythe path.
4. A frame-by-frame video-editing computer software (PowerDirector 6) capable of reading the video file directly fromthe video.
5. Reference strip markers placed across the road surface as ascale in data reduction. The distance between two referencestrip markers is 2 m.
6. Distance measured (meters).The small- and medium-sized type motorcycles without ABS
(150 cm3 and below) used in this study represent 99% of the motor-cycles population in Malaysia (Hussain et al. 2005). Fig. 2 showssome participants with their own motorcycles. The motorcycleswere modified to have their brake light turned on for both brakes:pedal or lever. The cameras were located in the main station off-road where the brake response experiment took place to allowviews of the roadway from different positions. One of them waslocated where it could measure the speed of the motorcycle beforeand at the time the light is switched on. Other cameras were placedto determine the exact time between onset of the light by the road-side until the motorcycle brake light is illuminated; these viewscaptured the exact time that the participant applied the brake.
Procedures
Participants were individually examined under good conditions(e.g., daylight, good weather). Before arriving at the experimentallocation, the participants were tested for their visual acuity andcolor vision. All selected participants had a minimum of 20=40
vision, passed the color vision test, and were screened througha medical questionnaire for drug/alcohol consumption or any othermedical circumstances that could impair riding. Once the test wascompleted, the participants were guided to ride their motorcyclesto the starting point. They were then asked to adjust factors such asthe seat, mirrors, and helmet straps.
The researcher briefed the participants on the overall features ofthe test and explained the experimental process. The participantswere informed that they were going to take part in a study ofbraking performance. In addition, they were informed about thedirection of the test road and asked to ride the motorcycle alongthe experimental route a couple of times until they felt comfortable.The participants were told in advance that at some point along theroad, the light will be switched on. Thus they need to be alert toapply the brake as quickly as possible following activation of thelight, and they should modulate their braking to maintain direc-tional control. Their actions were captured using camcorders setto slow-motion mode. This is necessary so that the motorcycle,rider, and light could be seen from the main station. The locationwhere the motorcycle was completely stopped is measured in me-ters. Reference strip markers were placed across the road surface tomeasure the motorcycle’s complete stop location.
All 89 participants achieved braking maneuvers at speeds of ap-proximately 60 to 80 km=h on both wet and dry pavement condi-tions. Subjects who could not modulate their braking to maintaindirectional control (loss-of-control braking maneuver) were askedto repeat the test. Each session took between 10 to 15 min, and theparticipants were then given petrol voucher. To minimize the riders’expectancy, the light was not switched on approximately 15% ofthe time.
The capability of the camcorders to capture videos of movingmotorcycles in slow motion mode was utilized. The motorcyclespeed was measured before the rider applied the brake at the teststation. This was accomplished by using the video frames fromthe Samsung camcorder when the motorcycle arrived at the mainstation and before the light was switched on. Reference strip mark-ers placed across the roadway surface was used to measure thespeed of the motorcycle for each test.
To measure the braking distance, the image of the motorcyclewhen the brake light was switched on was observed using thePower DVD software. These images were then exported toAutoCAD 2007 software to define the motorcycle location. Refer-ence strip markers placed across the roadway surface was used asa scale in data reduction. The on-road measurement (actual value)was represented in different scales in the AutoCAD software foreach observation. The actual values of the motorcycle stop location
light
13 14 15 16 17 18 19 20 21 2212
Cameras
Fig. 1. Station of motorcyclist braking performance in expected object
Fig. 2. Participants with their own motorcycles (image by the authors)
were calculated in each picture according to its scale ratio. Finally,the distance between those onsets of the activation of motorcyclebrake light and the motorcycle complete stop was calculated.
A simple AASHTO equation was used to derive a constantdeceleration estimated from the actual stopping distance (Koppaet al. 1996; Gates et al. 2007):
a ¼ V2=2BD ð1Þ
where a = acceleration in m=s2; V =Motorcycle speed in m=s; andBD = braking distance in m.
Experimental Result 1
For each experiment of braking maneuvering, the following factorswere recorded:• Motorcycle location when the brake light was illuminated,• Motorcycle location when the motorcycle was completely
stopped, and• Motorcycle speed before the onset of the light.
To compute the deceleration rates and motorcycle approachspeeds, the travel time and distance obtained from the videos wereused. The time to travel between the time prior to the light wasilluminated and successive references signs were used to computeapproach speeds.
In this experiment, the deceleration rate was defined as the aver-age deceleration rate measured from the location where the brakelight was illuminated to the location where the motorcycle stoppedcompletely. The data for the vehicular observations were tabulated,organized, and coded into a single data file for detailed statisticalanalyses.
Fig. 3 displays the distribution of the deceleration rates for mo-torcycle riders on dry pavement. The decelerations for individualriders on dry pavement ranged from 2.28 to 7.14 m=s2.
The mean and standard deviation for the deceleration valueson the dry pavement were 4.59 and 1.04 m=s2, respectively. Fig. 3shows that the 5th and 10th percentiles of deceleration rates were2.96 and 3.30 m=s2, respectively.
The mean and standard deviation for the deceleration valueson wet pavement were 3.66 and 0.72 m=s2, respectively. Fig. 4shows the distribution of deceleration rates for motorcycle riderson wet pavement. The range of decelerations among the riders onwet pavement was from 1.86 to 5.41 m=s2. On wet pavement,the 5th percentile driver deceleration was 2.55 m=s2, whereas the
10th percentile motorcyclist deceleration was 2.77 m=s2. Table 1presents the values of deceleration rate for the different test condi-tions in Experiment 1.
The pavement condition of either wet or dry also contributedsignificantly to a difference in braking distance and decelerationrate. The braking distances were compared with the AASHTObraking distances for a design speed of 60 km=h, which was 41 m.In this study, the riders exhibited a 90th percentile braking distanceof 51 m on wet pavement, whereas the AASHTO braking dis-tance is shorter. The difference in deceleration rate for male andfemale riders is small and not significant.
Experimental 2 (Unexpected Object)
Participants
Similarly, the test subjects for this experiment were also recruitedand screened from Universiti Putra Malaysia. Of the sixteen re-cruited motorcycle riders (8 males and 8 females), 8 riders wereolder than 16 years old (4 males and 4 females), whereas 8 riderswere 50 years or older (4 males and 4 females).
Equipment
The entire system for the unexpected PRT measurement was sim-ilar to Experiment 1, except that a yellow fabric obstacle was added(Fig. 5). The obstacle should be chosen as to avoid undesirable con-sequences in cases of a crash between the obstacle and motorcycle.The obstacle needed to be flexible so as not to shatter or be tornapart if hit by a motorcycle. More importantly, it should not damagethe motorcycle. The visibility of this obstacle ought to be in a waythat the rider could apply the motorcycle brakes as soon as theobstacle was detected across the road. Therefore, a piece of fabricbarricade (1 m high and 3 m long) was used as an obstacle in thisstudy. One side of the fabric is bright yellow but the other side is the
Fig. 3. Distribution of motorcyclist deceleration rates on dry pavementin expected object
Fig. 4. Distribution of motorcyclist deceleration rates on wet pavementin expected object
Table 1. Deceleration Percentile Values for Experiment 1 (m=s2)
same color as asphalt so that it is not detected by the riders until itsuddenly appeared across the road.
Procedures
Experiment 2 was carried out under the same conditions asExperiment 1, including the visual tests, questionnaire, medicalscreening, and familiarization with motorcycles.
Experiment 2 concentrated only on the unexpected brake reac-tion time. The key component of this experiment was that riderswere not told that their brake response times were going to bemeasured. The session began with guiding the participants to theirown motorcycles. The participants were informed that they aregoing to take part in an evaluation of exclusive motorcycle lanes.This protocol was used to ensure that the participants did notpredict a braking scenario. The participants were instructed to ridethe motorcycle along the experimental path a couple of times untilthey are relaxed and familiar with the route. Fig. 6 illustrates themain station of the experimental route.
All participants were told to maintain a speed of approximately60 km=h while riding along the experimental route. The partici-pants rode once through the main station where the obstacle wasplanned to appear. However, nothing happened just to make surethat they were not expecting any kind of braking scenario. For thesecond practice task, the subjects later rode back to the startingpoint. This time, the riders rode along the experimental route
similar to the first experiment and the data was collected.Throughout this task, the obstacle was unexpectedly made to ap-pear in front of the motorcycle riders near the main station of thetest route. Camcorders took videos in slow motion mode so thatthe motorcycle, motorcyclist, and obstacle could be observed.Therefore, the time between the appearance of the obstacle andthe initial onset of the activation of the motorcycle’s brake lightwas recorded.
At the end of Experiment 2, when the participants stopped themotorcycle for the obstacle, they were then briefed about the pur-pose of the obstacle and the reason why they could not be informedearlier. The participants were then asked to read and sign a briefingform and requested not to mention the experimental procedure toanyone else for the next two months. Each session took between20 to 30 min and the participants were given petrol vouchers.
Experimental Result 2
Similar to Experiment 1, the following parameters were recordedfor each experimental braking maneuver:• Motorcycle location when the brake light was activated,• Motorcycle location when the motorcycle was completely
stopped, and• Speed of the motorcycle before the appearance of an unexpected
object.The same process and procedure as in Experiment 1 were used
to compute the approach speeds and deceleration rates. The datawere organized and coded into a single data file for detailedstatistical analyses.
cameras
Obstacle(Fabric barricade )
13 14 15 16 17 18 19 20 21 22
12
Fig. 6. Obstacle (fabric barricade) suddenly appeared on the road path
Fig. 5. Fabric barricade use as unexpected object (image by theauthors)
Fig. 7. Motorcyclist deceleration distributions to an unexpected object
The braking distance values were analyzed to provide the brak-ing distance for a completely unexpected object and compared withthe braking scenario in the previous AASHTO braking distanceexperiment.
The decelerations varied widely among the riders. A mean valuefor all riders was 6.02 m=s2 with a standard deviation of 1.32 m=s2.Fig. 7 shows the distribution of deceleration rates of motorcycleriders for tests involving unexpected object. The range of deceler-ations among the riders was from 3.42 to 8.12 m=s2.
The result of braking distance maneuvering for an unexpectedobject was shorter than for an expected object. This may be becausethe obstacle appeared dangerous, which led the test subjects toapply higher deceleration to stop completely. An average rider’sbraking distance to an unexpected obstacle was 52 m at a speedof 60 km=h.
Conclusions and Recommendations
Two different field studies were undertaken to investigate motorcy-clists’ braking performance to an unexpected object and an ex-pected object along the roadway. The study design used a testroad that was exactly the same as motorcycle lanes in Malaysiato measure braking distances and decelerations. The study designallowed for differences in motorcycle handling and rider capabil-ities associated with wet and dry pavement conditions.
Results showed that when riders were faced with the need tostop for an unexpected object along the roadway, the mean andstandard deviation of deceleration were 6.02 and 1.32 m=s2,respectively, and most riders chose decelerations greater than3.42 m=s2. These results are similar to that of other studies byEcker et al. (2001) and Vavryn and Winkelbauer (2004). In thesestudies, the riders made a complete stop emergency braking maneu-ver on dry pavement. It was found that the average motorcyclistbraking deceleration in response to an unexpected object was6.02 m=s2, which is less than the average braking decelerationfor passenger cars under similar conditions (5.7 m=s2) as con-ducted by Fambro et al. (2000). Motorcycle braking has somepeculiarities that are different from passenger cars. Motorcyclesare inherently less stable than passenger cars and rely on riders toremain upright during braking maneuvers.
Study results also showed that the braking distance in experi-ments with an unexpected object is shorter than for an expectedobject. Also, the braking distance on a wet pavement is longerthan on dry pavement. Riders’ gender was found to be insignificantfor deceleration rate.
About 90% of all riders chose decelerations that were greaterthan 2.75 m=s2. These decelerations were within riders’ capabil-ities to stay in their lane (direction) and maintain steering controlduring the braking maneuver on wet surfaces (comfortable stop-ping). Less than 65% of riders used a deceleration rate greater than3.4 m=s2, the value specified by AASHTO in the Green Book asthe threshold for comfortable stopping. According to this study,more than 35% of riders could not stop comfortably with a decel-eration rate of 3.2 m=s2. This indicated that all roads were designedin accordance with AASHTO guidelines and may not provide therequired sight distance for most motorcyclists, especially at hori-zontal curves.
Further, the results showed that motorcyclists had more prob-lems with the braking distance on wet pavements along the exclu-sive motorcycle lanes in Malaysia, especially with respect to therequired sight distance. This is because, as mentioned previously,exclusive motorcycle lanes were designed based on the cross-reference design criteria for cycle tracks and highways.
From the motorcyclists’ deceleration rate and braking dis-tance found in this study, the following recommendations aresuggested:• 90% of all riders will decelerate at least 2.75 m=s2 on wet pave-
ment and 3.30 m=s2 on dry pavement. Therefore, 2.75 m=s2
(comfortable deceleration for most riders) is recommended asthe deceleration threshold for determining required motorcyclestopping sight distance in exclusive motorcycle lanes.
• In countries where motorcycles are heavily used, the roadsshould be evaluated for provisions of adequate motorcyclestopping sight distance, especially if the roads were designedaccording to AASHTO guideline.
• The effect of motorcycle braking performance under dif-ferent conditions in the geometric designs of roads should beinvestigated. This is also recommended for developed coun-tries considering that motorcycle registrations and motorcy-clist deaths and injuries have increased in recent years(Haworth 2012).
• Sight distance and braking distance on existing exclusive mo-torcycle lanes in Malaysia according to the motorcycle stoppingsight distance should be investigated. It is recommended that,where there is inadequate motorcycle stopping sight distancealong exclusive motorcycle lanes, then motorcycle speed needsto be reduced.
• The use of motorcycles with ABS equipment should be encour-aged to increase the rider deceleration rate, because studies con-ducted on closed test tracks have demonstrated that ABS canreduce motorcycle stopping distances (Vavryn and Winkelbauer2004; Green 2006).
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