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The Singapore Law Gazette

Contributory Factors to Motorcycle Accidents


Compared with cars and other four-wheelers, motorcycles are economical in terms of vehicle ownership, running costs, fuel economy, parking fees and maintenance. Motorcycles offer the convenience of manoeuvring easily through congested roads and require less parking space than four-wheelers. Motorcycle usage has also increased in tandem with the growth of e-commerce and food deliveries.

Motorcyclists, cyclists and pedestrians are often categorised as vulnerable road users (VRUs). Key disadvantages of operating a motorcycle are exposure to the elements and adverse weather, sensitivity to bumps and road defects, and physical vulnerability in the event of an accident. When involved in traffic accidents, motorcyclists often sustain multiple or fatal injuries. They generally suffer more injuries than drivers due to the smaller size, much lighter weight, and the limited safety features of motorcycles. Motorcyclists can only rely on their helmet and safety gear to absorb impact forces and reduce abrasion, unlike drivers in enclosed vehicles which are equipped with bumpers, impact bars, crumple zones, airbags and seatbelts.

A rear-ended motorcycle may result in loss of control and serious injury or fatality, whereas impacting a four-wheeler may result in merely a dented bumper. In an impact or loss of control at high speed, the motorcyclist is often thrown far and hard on the road surface and may forcefully strike a fixed roadside object. An injured fallen motorcyclist lying on the road may be run over by another vehicle.

Motorcycle Accident Statistics

According to the 2020 Land Transport Authority (LTA) statistics,1LTA Annual Vehicle Statistics 2020, Singapore had 141,403 motorcycles and scooters (i.e. 14.5 per cent) out of a total motor vehicle population of 973,990. Motorcyclists, scooter and pillion riders are generally at increased risk of fatality.2Wong, Zeng Hao, et al. “A review of fatal road traffic accidents in Singapore from 2000 to 2004.” Annals Academy of Medicine Singapore 38.7 (2009): 594. Year after year, this at-risk group is significantly over-represented in traffic crashes and fatalities. In 2020,3Police News Release Annual Road Traffic Situation 2020, Public Affairs Department, Singapore Police Force 10 February 2021 motorcyclists and pillion riders accounted for 3,381 casualties, and 51 (60 per cent) out of a total of 85 fatalities. Motorcycles were involved in more than 63 per cent of the 82 fatal accidents in Singapore. Previous studies indicate the risk of mortality for motorcyclists to be 18.8 times that of car drivers in Singapore.4Wong, Evelyn, et al. “Road traffic accident mortality in Singapore.” The Journal of emergency medicine 22.2 (2002): 139-146.

Distinct Characteristics and Vulnerabilities of a Motorcycle

The general objective of traffic accident reconstruction is to determine the circumstances in which the traffic collision occurred.5Traffic Accident Reconstruction – A primer for lawyers, The Forensic Experts Group, Law Gazette, January 2017 To reconstruct motorcycle accidents, the forensic expert needs to take into consideration the distinct characteristics of motorcycles and riders, including the following:

a) Exposure to noise and vibrations:

Motorcyclists are more exposed than car drivers to high noise levels6Quieter cars from 2023 under new noise standards. Christopher Tan, Straits Times, 8 April 2021 which can cause discomfort, distraction and hearing damage and loss. Noise comes from the motorcycle engine during initial acceleration, and from other vehicular traffic and air rushing over the helmet when the motorcycle reaches a high speed on roads and expressways. Comparing with the average human pain threshold of 110 decibels, motor vehicles may emit noise levels of between 96 and 100 decibels. Motorcyclists are exposed to whole-body and hand-arm vibrations transmitted from the motorcycle engine to the seat, handle-bars and footrests. These vibrations may cause physical effects such as hand cramps and numbness, and circulation problems. In general, vibrations are greater at higher speeds, for older motorcycles and single-cylinder motorcycles, and in the presence of road surface irregularities.

b) Stability and control:

A motorcycle is typically a two-wheeled, single-track vehicle, which is inherently unstable to external forces. Motorcycles lack lateral stability when stationary and need to be in forward motion to stay upright. They are susceptible to toppling, loss of control, skidding and sliding on the road surface. When cornering or negotiating a bend, the motorcyclist need to “lean” to maintain balance. The pillion rider has to lean in the same direction as the motorcyclist in order not to destabilise the motorcycle.

Riding a motorcycle is generally more complex and requires more eye-hand and foot coordination skills and attention than driving a car. Riding is also physically more demanding and tiring than driving. Even a minor contact, such as a side swipe, with another vehicle moving at moderate or high speed, or encountering a road defect (pothole, uneven level) or contaminant (debris, oil, sand) can be disastrous for a motorcyclist. Accidental spillage of sand, gravel or soil on the road surface from a passing lorry creates such hazards. A broken, bumpy or contaminated road surface can adversely affect a motorcycle’s balance, stability, brake effectiveness and stopping distance. Panic hard braking can also destabilise a motorcycle, lock the front or rear wheel, and cause the bike to flip over, fishtail or slide, particularly on wet or sandy roads. During wet weather conditions, unlike a motorist in a car that is equipped with windshield wipers and defroster, the motorcyclist is exposed to the rain and any visor or shield worn over his face may fog, posing challenges to his vision.

c) Manoeuvrability and riding behaviour:

The small size and high acceleration capability of motorcycles increases their manoeuvrability and ability to move in smaller, tighter spaces. Road lanes are often wide enough to allow a motorcycle to move alongside a car or another motorcycle within the same lane.

  • Lane-splitting, a common behaviour on the roads, refers to the riding of a motorcycle between two adjacent lanes of traffic heading in the same direction. Motorcycles often ride along or near the white lane boundaries instead of occupying the middle of a lane.
  • Lane filtering refers to the riding of a motorcycle through stopped or slow-moving traffic. Motorcycles often pass between conventional vehicles and filter longitudinally and laterally through gaps to get to the front of the group. During the red-light phase at a traffic junction, motorcycles often filter to the stop line in front of stopped vehicles and accelerate forward once the light turns green.

d) Small signature:

Although the narrower and shorter size of motorcycles enable them to exploit unoccupied road space between other traffic that larger vehicles are unable to use, this characteristic may also place motorcycles in the blind zones of four-wheelers. Motorcycles may also be hidden behind larger vehicles. The small size may create the illusion that the motorcycle is farther away than in reality. Having a small, less conspicuous profile, and accounting for only one in seven motor vehicles in Singapore, motorcycles are at times not seen or expected by other motor vehicle drivers. Due to its lower weight compared to cars, a motorcycle often has a higher engine power-to-weight ratio and higher acceleration than most motor cars.

Measures to Increase Conspicuity and Minimise Motorcycle Accidents

Various measures have been adopted and implemented to increase motorcycle conspicuity. In November 1995, Singapore implemented the “ride-bright” legislation requiring motorcyclists to switch on their headlamps even when travelling in the daytime. Research7Yuan, Wu. “The effectiveness of the ‘ride-bright’ legislation for motorcycles in Singapore.” Accident Analysis & Prevention 32.4 (2000): 559-563. indicated that the implementation of daytime running lights has reduced the number of fatal and serious injury motorcycle accidents. Since 1 November 1997, every motorcycle first registered in Singapore8Road Traffic Act (Chapter 276, Sections 6 And 140) Road Traffic (Motor Vehicles, Lighting) Rules has to be equipped with a device to automatically switch on the headlamp of the motorcycle when the ignition switch is turned on, and to remain lit at all times while the engine is running.

Types of Motorcycle Accidents

Good hazard perception and response are essential to safe defensive riding. Motorcyclists can be involved in single or multi-vehicle accidents. Right turns, overtaking, lane change, merging and filtering manoeuvres account for many motorcycle-related collisions.

  1. Single-vehicle accidents usually involve the motorcycle departing from the roadway (run-off-road) or colliding into a fixed roadside object such as a guard-rail, lamp post, traffic signal light or tree. A novice rider misjudging and entering a tight bend at too high a speed may make a wide turn and place himself in a dangerous situation.
  2. Multiple-vehicle accidents: Motorcycles may also be involved in rear-end, head-on, sideswipe and broadside (T-bone) traffic collisions. Rear-end collisions may result from the motorcycle riding too close to the vehicle in front which suddenly braked, or the tailgating vehicle striking the rear end of the motorcycle due to excessive speed or impaired driving. It may also be associated with motorcycles in the blind zones of four-wheelers, such that they are not seen by drivers intending to change or merge lanes or make turns, or moving off from stationary or a stopped position at a traffic junction.

Contributory Factors of Motorcycle Accidents

General contributory factors to traffic accidents have been described in a previous article.9Contributory Factors to Traffic Collisions, The Forensic Experts Group, Law Gazette, November 2020 Contributory factors more frequently at play in motorcycle accidents include the following:

  1. violation of traffic rules and signs by drivers and/or motorcyclists;
  2. travelling at inappropriate speed;
  3. impairment due to loss of ability, illness, alcohol, drugs, fatigue;
  4. risk-taking and aggressive behaviour;
  5. inattention, distraction;
  6. expectancy, perception and judgment errors;
  7. poor manoeuvre execution;
  8. small signature and poor conspicuity; and
  9. weather-related problems and road conditions;

Poor Conspicuity

Motorcycles present a smaller frontal area compared to cars and hence, appear less conspicuous. To make matters worse, some riders have a tendency to wear dark helmets and dark coloured clothing, further reducing their conspicuity especially at night. Studies have found that wearing reflective or fluorescent clothing and white or light coloured helmets and using headlights in daytime could reduce serious injuries or death from motorcycle accidents by up to a third10Wells, Susan, et al. “Motorcycle rider conspicuity and crash related injury: case-control study.” Bmj 328.7444 (2004): 857..

Poor conspicuity increases the risk of motorcycle collision related injury. A side swipe may occur when the motorcycle making a turn overtakes a large vehicle that was making the same turn because the driver may fail to see the motorcycle, which was in its blind zone. Likewise, it may be dangerous for a motorcycle to filter to the stop line in front of a large, stopped vehicle at a traffic junction because the motorcycle may be hidden in the vehicle’s blind zone. When the traffic light turns green, the motorcycle may be rear-ended unless it accelerates forward earlier than the large vehicle.

Violation of Traffic Rules and Controls

Right-of-way violation collision is a common type of motorcycle accident. An on-coming motorcycle that runs the red light can violate the right-of-way of another vehicle already in the process of turning right in the traffic junction. Conflict can also occur when another vehicle making a discretionary (permissive) right turn at a traffic junction, or exiting from a side road onto a main road, or merging into the lane of the motorcycle violates the motorcyclist’s right-of-way.

Drivers may fail to slow down at the turning pocket or stop-line at a junction to conduct proper checks for an oncoming motorcycle. Drivers turning right may also fail to give way to motorcyclists entering the junction late, during the All-Red period. This hazardous situation may occur despite drivers looking in the right direction and the two-wheeler being visible, because drivers may focus on the more distant view further upstream from the junction, and inadvertently overlook the immediate foreground. In such collisions, the driver failed to see the motorcycles while turning until the final critical moments before the collision.

Failure to Provide Timely Signals and Cues

All drivers and motorcyclists have a duty to provide timely signals to communicate their intentions so that other road users have sufficient time to perceive and react appropriately. Traffic conflicts may be created by motorcyclists who fail to signal before turning at intersections or changing lanes.

Motorist Expectation

Expectancy is another important reason why many motorists fail to perceive an approaching motorcycle. For instance, if a driver travelling in the same lane behind a motorcyclist observes the motorcycle filter to the rightmost right-turning lane near a traffic junction, the driver may expect the motorcyclist to perform a right turn, and decide to speed up. A collision or near-collision may occur if the motorcyclist suddenly decides to filter back to his original lane, directly in front of the driver. Driver expectation can form a lethal combination with blind zones. Drivers do not expect and may be caught off-guard by motorcycles that split lanes and overtake cars within the same lane; such motorcycle manoeuvres may cause sideswipe accidents.

Judgment Error

Motorcycle collisions can occur at traffic junctions because of the driver’s erroneous judgment of speed, acceleration, distance and arrival time of the motorcycle. Drivers may incorrectly estimate that motorcycles would reach them later than cars because motorcycles appear more distant due to their smaller sizes. Larger approaching vehicles appear more threatening and closer than smaller ones.

On the other hand, the motorcyclist who was travelling straight ahead across the junction may be riding at excessive speed, such that the other vehicle could not detect its presence before proceeding to make the discretionary right turn, resulting in a T-bone collision. Red-light running and speeding are high-risk and very dangerous riding behaviours. These traffic violations often lead to serious injuries and fatalities in motorcycle accidents.

Experience and training generally correlate to visual scanning skills, hazard perception, judgement, decision-making, evasive action and response times in motorcyclists. Experienced riders usually handle unanticipated circumstances such as bad weather, sharp bends, road defects, traffic conditions and conflicts better than inexperienced riders.

Alcohol Impairment

Blood Alcohol Concentration (BAC) has been implicated in many motorcycle fatalities. Similar to drink driving, alcohol-affected motorcycle riders are more likely than non-drinking riders to lose control of their motorcycles. Alcohol generally impairs motorcycle riding skills:11Creaser, Janet I., et al. “Effects of alcohol impairment on motorcycle riding skills.” Accident Analysis & Prevention 41.5 (2009): 906-913. intoxicated riders have slower response times and adopted larger tolerances towards hazard avoidance, leading to more task performance errors.


Distraction, boredom and inattention can affect any road user. A rider’s attention may be divided among multiple riding tasks such as signaling, turning and monitoring traffic. Being distracted or inattentive is likely to result in not noticing other vehicles or only seeing them when it is too late to avoid the collision. The consequences of losing concentration at a higher speed are often more serious than at a lower speed.

Case Studies

Case Study 1: Rear end collision of a motorcycle in the front blind zone of a prime mover12Forensic Science – Briefs for the Legal Practitioner. The Forensic Experts Group, Lexis Nexis (2017). 

A prime mover stopped at the traffic junction on Paya Lebar Road towards Tanjong Katong Road, as the light had turned red. Unknown to the driver of the prime mover, a motorcycle had passed the prime mover on its left and manoeuvred to the area just in front of the heavy vehicle. When the traffic light turned green seconds later, the prime mover driver moved off first, resulting in a rear-end collision with the motorcycle. The rider was run over and killed, while his pillion rider fell to the left side of the prime mover, and thus survived the accident.

The Coroner’s Inquiry was aided by traffic accident reconstruction, which revealed that the design of the prime mover and the short stature and driving posture of the driver were primary factors resulting in a large forward zone, large enough for the motorcycle to be concealed in. The prime mover driver did not see the motorcycle filtering forward on his left and stopping near the front of the prime mover. The driver had moved off and only realised that something was amiss when he heard sounds of his vehicle going over an object on the road.

Case study 2: Side-impact collision during a permissive right turn

A car waiting at a four-way junction began making a permissive right turn on a green traffic signal. A motorcyclist travelling on the opposite carriageway which had right of way entered the junction and collided into the left side of the car, sustaining serious injuries. Through video analysis, TFEG found that the motorcycle was travelling at about 79 km/h when approaching the traffic junction, although the posted speed limit was 50 km/h. Had the motorcycle been travelling within the speed limit, the car would have completely cleared the junction before the motorcycle arrived, and a collision would have been averted. A vehicle in violation of the speed limit and approaching much faster than expected can upend another motorist’s erstwhile valid gap selection, contributing to a traffic collision.

Case study 3: Side-impact collision between two motorcycles travelling on the same lane

A traffic collision occurred between two motorcycles (A and B) which were travelling along the 4-lane Bartley Road East. Prior to the collision, Motorcycle A was travelling on the right side of Lane 3 whilst Motorcycle B with its pillion rider, was travelling behind Motorcycle A, on the left side of same lane. Motorcycle B was in the process of riding past Motorcycle A when the latter started to lean left to turn into a minor road. This led to the left side of Motorcycle A and the right side of Motorcycle B coming into forceful contact with each other. The resulting fall caused serious injuries to the pillion rider.

TFEG determined the trajectories, calculated the speeds of the motorcycles, evaluated the factors contributing to the collision, and rendered an expert opinion on whether the collision could have been avoided. The following actions of both motorcyclists contributed to the collision:

  • Motorcyclist A’s lack of sufficient attention to upstream traffic, failure to conduct adequate checks before turning, and his late execution of the left turn, and
  • Motorcyclist B’s excessive speed of travel and his misperception of Motorcycle A’s intention to turn left (rider expectancy). Motorcycle B was likely unaware that Lane 3 was both straight-going and left-turning, due in part to Motorcycle A’s misleading movements, and the misleading directional arrows on Lane 3.

The forensic report was helpful to shed light on the circumstances of the incident. The three parties averted the High Court hearing after agreeing to a consent judgement in favour of the pillion rider.

Case study 4: Road contaminants leading to skidding of a motorcycle and a car

This collision between a car and a motorcyclist on an expressway occurred at night in fine weather. As the car was driving up the left lane of the slip road ramp to merge onto the expressway, the driver saw a motorcycle skidding directly in front of him, and the motorcyclist falling onto the roadway. The driver braked hard but could not stop in time, colliding into the motorcyclist. The road surface on the left lane was found to be muddy.

TFEG carried out collision avoidance analysis by evaluating the possible evasive actions by the motorcyclist after falling from the motorcycle, and calculated the time to collision for the driver, and opined that the collision was unavoidable for the case. The following factors likely contributed to the incident:

  • Long stretch of road contaminated by a thick layer of mud;
  • Poor visibility and inconspicuity of this muddy patch on the road;
  • Low expectancy of the motorcyclist and the driver to the presence of thick wet mud on the road,
  • Low expectancy of the driver to the sudden skidding of the motorcycle and falling of its rider in his path; and
  • Significant reduction of traction and stability of the two motor vehicles. The two-wheeler motorcycle was more affected by the road contaminant, resulting in skidding on the muddy road and loss of control. The car was likely to have skidded when the driver applied hard braking to avoid the fallen motorcyclist. The stopping distance of the car increased due to the slippery road surface.


Motorcyclists and pillion riders are vulnerable road users who often suffer severe injuries and death in serious road traffic accidents. This at-risk group accounted for 60 per cent of fatalities in road traffic accidents in 2020 in Singapore. The motorcyclist’s account of circumstances and events leading to the accident would not be available in serious accidents.

The forensic expert first analyses and reconstructs the motorcycle accident using forensic examinations common to accident investigations, such as determining vehicle speeds and trajectories, sequence of events, nature of traffic conflict, nature of physical contact, line of sight, and human perception and reaction. However, given the distinctive characteristics of motorcycles and riders, an understanding of these additional characteristics and the contributory factors of motorcycle accidents is necessary for a more holistic evaluation, interpretation and reconstruction, as well as collision avoidance analysis of the accident.


1 LTA Annual Vehicle Statistics 2020,
2 Wong, Zeng Hao, et al. “A review of fatal road traffic accidents in Singapore from 2000 to 2004.” Annals Academy of Medicine Singapore 38.7 (2009): 594.
3 Police News Release Annual Road Traffic Situation 2020, Public Affairs Department, Singapore Police Force 10 February 2021
4 Wong, Evelyn, et al. “Road traffic accident mortality in Singapore.” The Journal of emergency medicine 22.2 (2002): 139-146.
5 Traffic Accident Reconstruction – A primer for lawyers, The Forensic Experts Group, Law Gazette, January 2017
6 Quieter cars from 2023 under new noise standards. Christopher Tan, Straits Times, 8 April 2021
7 Yuan, Wu. “The effectiveness of the ‘ride-bright’ legislation for motorcycles in Singapore.” Accident Analysis & Prevention 32.4 (2000): 559-563.
8 Road Traffic Act (Chapter 276, Sections 6 And 140) Road Traffic (Motor Vehicles, Lighting) Rules
9 Contributory Factors to Traffic Collisions, The Forensic Experts Group, Law Gazette, November 2020
10 Wells, Susan, et al. “Motorcycle rider conspicuity and crash related injury: case-control study.” Bmj 328.7444 (2004): 857.
11 Creaser, Janet I., et al. “Effects of alcohol impairment on motorcycle riding skills.” Accident Analysis & Prevention 41.5 (2009): 906-913.
12 Forensic Science – Briefs for the Legal Practitioner. The Forensic Experts Group, Lexis Nexis (2017). 

About The Forensic Experts Group (TFEG): TFEG is Singapore’s first private independent company and one-stop centre offering a wide spectrum of forensic expertise to serve the needs of a diverse emerging market. Our scientific capabilities span many forensic disciplines and can be applied to areas such as traffic collisions, industrial incidents, fraudulent documents, counterfeit products, and chemical-related fires and explosions.

TFEG is a team of accomplished scientists led by former senior consultant forensic scientists from the Health Sciences Authority, Singapore. Our senior scientists envisioned, pioneered and established many forensic capabilities and services in the government laboratory since 1989. Through TFEG, we now combine our many years of specialised knowledge, unique experience and skillsets to deliver top quality forensic services to the larger local and overseas market.

While at the Health Sciences Authority, TFEG experts have testified in numerous court trials, including many prominent and high-profile cases. Since the inception of TFEG in 2013, our experts have been providing expert testimony in the local and overseas court, arbitration and mediation proceedings, and also assisted legal practitioners in reviewing and understanding expert reports.