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Safety implications oflane-splitting among California motorcyclists
involved in collisions
Report To
California Office of Traffic Safety
By
ThomasRice
LaraTroszak
Safe Transportation Research & Education Center
University of California Berkeley
August 6, 2014
Purpose
This documentsummarizes an analysis of preliminary data from the California Enhanced Motorcycle
Collision Data Project. We report the prevalence of lane-splitting among approximately 8,000
motorcyclists who were involved traffic collisions in June 2012 through August 2013 and examine how
other characteristics vary by whether the motorcyclist was lane-splitting.
Background
Supplemental data were collected as part of a two-year collaboration between the Safe Transportation
Research & Education Center at the University of California Berkeley and the California Highway Patrol.
Funding was provided by the California Office of Traffic Safety.
The goal of the project wasto obtain information not usually collected during law enforcement
investigations of motorcycle traffic collisionsin California. A one-page supplemental data form was used
during collision investigations by CHP officers and by officers at more than 80 allied law enforcement
agencies in the state. CHP officers completed the forms using an encrypted web site linked to the
software used to complete other traffic collision forms. Supplemental forms from allied agencies were
mailed to CHP and were forwarded to UC Berkeley for key entry. CHP officers used the supplemental
form from August 1, 2012 through July 31, 2013, and participating allied agencies used the form from
June 1, 2012 through May 31, 2013. A small number ofsupplemental forms were submitted in August
2013 and those are included in this analysis.

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The data collected on the form included driver license status, whether the motorcyclist was lane- splitting,speed of the motorcycle,speed ofsurrounding traffic, and for each motorcycle rider--helmet
type, helmet standard labeling (DOT, Snell, etc), helmet damage, helmet retention, body region injured,
fatality status, whether the rider was transported by EMS, BAC, and the use of high visibility or reflective
gear(See attached supplemental form).
The project resulted in the creation of a new database of information from 7,836 California
motorcyclists involved in collisions and the passengersinvolved in those collisions. Of these supplement
forms, 6,333 were submitted by CHP (81%) and 1,503 were submitted by allied agencies (19%). These
collisions involved a total of 8,262 motorcycle riders (7,836 operators and 426 passengers).
We refer to motorcyclists who were lane-splitting as LSM throughout this report.
Results
The first 9 tablesshow the distribution ofselected collision and motorcyclist characteristics by the lane- splitting status of the 7,836 motorcyclists.
Of the 7,836 motorcyclists, (22%) were known to be unlicensed (Table 1). The proportion of
motorcycliststhat were unlicensed was moderately lower among LSM (18%) than among other
motorcyclists(22%).
LSM were much less likely to have been carrying a passenger (2%) than were other motorcyclists
(6%)(Table 2).
LSM were also less likely to be rear-ended (Table 3) by another vehicle (2.7%) than were other
motorcyclists(4.6%).
LSM, on the other hand, were much more likely to have rear-ended another vehicle (36.4%) than were
othermotorcyclists(14.9%)(Table 4).
Alcohol use (Table 5) was low among these motorcyclists(3%). The prevalence of alcohol use was lower
among LSM (1.3%) than it was among other motorcyclists (3.3%).
The day of week of the collision varied greatly by lane-splitting status (Table 6). Among LSM, 14.6% of
collisions occurred on a Saturday or Sunday, compared with 34.9% of collisions among non-lane-splitting
motorcyclists.
Time of day also varied greatly by lane-splitting status (Table 7)--59.5% of LSM were involved in
collisions between 6-8:59 am or 3-5:59 pm, compared with 37.3% of motorcyclists who were not lane- splitting.

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The helmets used at the time of collision also differed by lane-splitting status. LSM were more likely to
be wearing a full-face helmet than other motorcyclists (79% and 64%, respectively) and less likely to be
wearing a novelty helmet (1.9% and 4.1%, respectively). Motorcyclists who were not lane-splitting were
more likely to wearing a 1/2- or 3/4-helmet (23%) than LSM (13%).
Patterns of injury were significantly different comparing LSM and other motorcyclists(Table 9). LSM
were notably less likely to suffer head injury (9.1% vs 16.5%), torso injury (18.6% vs 27.3%), or fatal
injury (1.4% vs 3.1%) than other motorcyclists. The occurrence of neck injury and arm/leg injury did not
differ meaningfully by lane-splitting status.
Table 10 tabulates lane-splitting motorcyclists by whether their lane-splitting was being done with over
a 10 MPH differential of speed compared to surrounding traffic and whether lane-splitting was done
when surrounding traffic was traveling at speeds greater than 30 MPH. Of the 1,163 lane-splitting
motorcyclists, 419 (36.1%) were lane-splitting in a manner consistent with one of the speed
components (but not both), 240 (20.6%) were lane-splitting consistent with both components, and only
39 were lane-splitting consistent with neither component. A large number of these lane-splitting
motorcyclists were missing information on the speed of the motorcycle and/or the surrounding traffic
(40%); the manner in which these motorcyclists were lane-splitting is unknown.
Categories of motorcycle speed and traffic speed are shown in Table 11. It can be seen that a relatively
small proportion of lane-splitting is done in fast flowing traffic—95 motorcyclists were lane-splitting in
traffic flowing 31-50 MPH, compared with 426 motorcyclistslane-splitting in traffic following at 1-30
MPH. It can also be seen that the motorcycle speed almost always exceeds the traffic speed, at times by
a considerable margin. For example, in traffic flowing at 31-50 MPH, the motorcyclist was traveling at
51-70 MPH in 29 instances.
Table 12 showsthe injury status of lane-splitting motorcyclists by the manner in which they were lane- splitting. Motorcyclists were categorized by whether their lane-splitting was done in a manner consistent
with safe and prudent lane splitting — consistent with the traffic speed component only, the motorcycle
excess speed component only, both components, neither component, and unknown status. Motorcyclists
who were lane-splitting consistent with both components had the lowest proportion of each injury type.
Motorcyclists who were lane-splitting consistent with only one component had higher proportions with
each injury type. Motorcyclists who were lane-splitting consistent with neither component had the highest
proportion with each injury type. For example, the proportion of motorcyclists with head injury was 6.3%
for those lane-splitting consistent with both components, 10.7% for those lane-splitting in traffic flowing at
30 MPH or less but exceeding the traffic speed by more than 10 MPH, 9.0% for those lane-splitting in
traffic flowing faster than 30 MPH but exceeding traffic speed by less than 10 MPH, and 20.5% for those
who were lane-splitting in traffic flowing at more than 30 MPH and who were exceeding traffic speed by
more than 10 MPH.

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Discussion
This preliminary analysis found that LSM who were involved in traffic collisions and who were included
in the Enhanced Motorcycle Collision Data Project had significantly different characteristics than other
motorcyclists. LSM were better helmeted than other motorcyclists. LSM were less likely to suffer head
injury, torso injury, and fatal injury than other motorcyclists. They were also more likely to be involved in
weekday collisions and more likely to be involved in collisions during peak traffic times (6-9 am and 3- 6
pm). LSM were less likely to be rear-ended but more likely to have rear-ended another vehicle than other
motorcyclists.
Additionally, we found significant variation in the manner in which lane-splitting was done. Lane- splitting was done in traffic flowing at a range of speeds. The motorcycle speed almost always exceeded
the traffic speed by a small margin but, in many cases, exceeded it greatly. We compared the
proportion of collision-involved, lane-splitting motorcyclists with injury across several body regions by
whether the lane-splitting was done only in traffic flowing at 30 MPH or less and that the motorcycle
speed should exceed the traffic speed by no more than 10 MPH. We found that the proportion with
each injury type was high when the lane-splitting was consistent with neither speed component, was
lower when it was consistent with one speed component, and was lower still when it was consistent
with both speed components.
This analysis has limitations. We used data from the Enhanced Motorcycle Collision Data Project. This
data set is lacking information on some basic factors that are needed for a more comprehensive analysis.
These factorsinclude rider age, rider gender, motorcycle characteristics, and numerous
collision and roadway characteristics. Information on these factors is being acquired in a related project
and will available for inclusion in future analyses of lane-splitting. We used broad categories of traffic
and motorcycle speed in this analysis; future work will include a more detailed examination of how lane- splitting characteristics vary by rider, motorcycle, collision, and roadway types.

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Tables
1. License status by lane-splitting status
License Status
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
No 5,078 77.0% 931 80.1% 60 74.1% 6,069 77.5%
Yes 1,456 22.1% 208 17.9% 17 21.0% 1,681 21.5%
Unknown 58 0.9% 24 2.1% 4 4.9% 86 1.1%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
2. Passenger status by lane-splitting status
Passenger
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
No 6,194 94.0% 1,138 97.9% 78 96.3% 7,410 94.6%
Yes 398 6.0% 25 2.1% 3 3.7% 426 5.4%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
3. Whether motorcycle was rear-ended by lane-splitting status
MC was Rear-Ended
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
No 6,253 94.9% 1,129 97.1% 71 87.7% 7,453 95.1%
Yes 304 4.6% 31 2.7% 4 4.9% 339 4.3%
Unknown 35 0.5% 3 0.3% 6 7.4% 44 0.6%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
4. Whether motorcycle rear-ended other vehicle by lane-splitting status
MC Rear-End Other Veh.
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
No 5,583 84.7% 737 63.4% 65 80.2% 6,385 81.5%
Yes 979 14.9% 423 36.4% 12 14.8% 1,414 18.0%
Unknown 30 0.5% 3 0.3% 4 4.9% 37 0.5%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%

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5. Alcohol involvement by lane splitting status
Alcohol Involvement
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
No 6,374 96.7% 1,148 98.7% 79 97.5% 7,601 97.0%
Yes 218 3.3% 15 1.3% 2 2.5% 235 3.0%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
6. Day of the week by lane-splitting status
Day of Week
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
Sunday 1,068 16.2% 70 6.0% 11 13.6% 1,149 14.7%
Monday 735 11.1% 149 12.8% 9 11.1% 893 11.4%
Tuesday 775 11.8% 207 17.8% 12 14.8% 994 12.7%
Wednesday 861 13.1% 232 19.9% 16 19.8% 1,109 14.2%
Thursday 865 13.1% 201 17.3% 8 9.9% 1,074 13.7%
Friday 1,029 15.6% 198 17.0% 8 9.9% 1,235 15.8%
Saturday 1,234 18.7% 100 8.6% 15 18.5% 1,349 17.2%
Unknown 25 0.4% 6 0.5% 2 2.5% 33 0.4%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
7. Time of day by lane-splitting status
Time of Collision
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
Mid-3:00 192 2.9% 6 0.5% 3 3.7% 201 2.6%
3:00-5:59 168 2.5% 25 2.1% 2 2.5% 195 2.5%
6:00-8:59 693 10.5% 298 25.6% 4 4.9% 995 12.7%
9:00-11:59 960 14.6% 102 8.8% 13 16.0% 1,075 13.7%
12:00-14:59 1,437 21.8% 143 12.3% 18 22.2% 1,598 20.4%
15:00-17:59 1,766 26.8% 394 33.9% 22 27.2% 2,182 27.8%
18:00-20:59 954 14.5% 168 14.4% 16 19.8% 1,138 14.5%
21:00-23:59 418 6.3% 27 2.3% 3 3.7% 448 5.7%
Unknown 4 0.1% 0 0.0% 0 0.0% 4 0.1%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%

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8. Helmettype by lane-splitting status
Helmet Type
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
Full-face 4,192 63.6% 921 79.2% 47 58.0% 5,160 65.8%
1/2 Helmet 948 14.4% 98 8.4% 8 9.9% 1,054 13.5%
3/4 Helmet 567 8.6% 56 4.8% 4 4.9% 627 8.0%
Any modular 303 4.6% 42 3.6% 6 7.4% 351 4.5%
Novelty 267 4.1% 22 1.9% 5 6.2% 294 3.8%
None 160 2.4% 5 0.4% 0 0.0% 165 2.1%
Unknown 155 2.4% 19 1.6% 11 13.6% 185 2.4%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%
9. Injury by lane-splitting status
Body Region
Lane-Splitting
No Yes Unknown Total
# % # % # % # %
Head Injury
No 5,504 83.5% 1,057 90.9% 66 81.5% 6,627 84.6%
Yes 1,088 16.5% 106 9.1% 15 18.5% 1,209 15.4%
Neck Injury
No 5,987 90.8% 1,078 92.7% 75 92.6% 7,140 91.1%
Yes 605 9.2% 85 7.3% 6 7.4% 696 8.9%
Torso Injury
No 4,794 72.7% 947 81.4% 64 79.0% 5,805 74.1%
Yes 1,798 27.3% 216 18.6% 17 21.0% 2,031 25.9%
Arm/Leg Injury
No 2,196 33.3% 480 41.3% 31 38.3% 2,707 34.5%
Yes 4,396 66.7% 683 58.7% 50 61.7% 5,129 65.5%
Fatal Injury
No 6,388 96.9% 1,147 98.6% 78 96.3% 7,613 97.2%
Yes 204 3.1% 16 1.4% 3 3.7% 223 2.8%
Total 6,592 100.0% 1,163 100.0% 81 100.0% 7,836 100.0%

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10. Speed status among lane-splitting motorcyclists
Speed Component Status No. %
Traffic speed* 252 21.7%
Speed differential** 167 14.4%
Neither component 39 3.4%
Both components 240 20.6%
Unknown 465 40.0%
Total 1,163 100.0%
* Motorcyclist lane-splitting in traffic flowing at 30 MPH or less
** Motorcyclist lane-splitting at no more than 10 MPH over traffic speed
11. Traffic speed by speed status among lane-splitting motorcyclists
Motorcycle speed
category
Surrounding traffic speed category
Not moving 1-30 MPH 31-50 MPH 51-70 MPH 71-99 MPH Unknown Total
No. % No. % No. % No. % No. % No. % No. %
Not moving 2 2.9% 2 0.5% 1 1.1% 2 2.0% 0 0.0% 3 0.7% 10 0.9%
1-30 MPH 46 65.7% 244 57.3% 5 5.3% 1 1.0% 0 0.0% 200 43.5% 496 42.6%
31-50 MPH 18 25.7% 128 30.0% 56 58.9% 6 6.1% 0 0.0% 135 29.3% 343 29.5%
51-70 MPH 3 4.3% 39 9.2% 29 30.5% 54 54.5% 3 23.1% 59 12.8% 187 16.1%
71-99 MPH 1 1.4% 9 2.1% 4 4.2% 32 32.3% 9 69.2% 21 4.6% 76 6.5%
100+ MPH 0 0.0% 0 0.0% 0 0.0% 3 3.0% 1 7.7% 4 0.9% 8 0.7%
Unknown 0 0.0% 4 0.9% 0 0.0% 1 1.0% 0 0.0% 38 8.3% 43 3.7%
Total 70 100% 426 100% 95 100% 99 100% 13 100% 460 100% 1,163 100%
* Motorcyclist lane-splitting in traffic flowing at 30 MPH or less
** Motorcyclist lane-splitting at no more than 10 MPH over traffic speed

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12. Injury by speed and speed differential status among lane-splitting motorcyclists
Body Region
Speed Component
Neither Traffic Speed* Speed Diff.** Both Unknown Total
# % # % # % # % # % # %
Head Injury
No 31 79.5% 225 89.3% 152 91.0% 225 93.8% 424 91.2% 1,057 90.9%
Yes 8 20.5% 27 10.7% 15 9.0% 15 6.3% 41 8.8% 106 9.1%
Neck Injury
No 32 82.1% 235 93.3% 155 92.8% 227 94.6% 429 92.3% 1,078 92.7%
Yes 7 17.9% 17 6.7% 12 7.2% 13 5.4% 36 7.7% 85 7.3%
Torso Injury
No 23 59.0% 209 82.9% 125 74.9% 211 87.9% 379 81.5% 947 81.4%
Yes 16 41.0% 43 17.1% 42 25.1% 29 12.1% 86 18.5% 216 18.6%
Arm/Leg Injury
No 9 23.1% 101 40.1% 57 34.1% 118 49.2% 195 41.9% 480 41.3%
Yes 30 76.9% 151 59.9% 110 65.9% 122 50.8% 270 58.1% 683 58.7%
Fatal Injury
No 38 97.4% 249 98.8% 165 98.8% 240 100.0% 455 97.8% 1,147 98.6%
Yes 1 2.6% 3 1.2% 2 1.2% 0 0.0% 10 2.2% 16 1.4%
Total 39 100.0% 252 100.0% 167 100.0% 240 100.0% 465 100.0% 1,163 100.0%
* Motorcyclist lane-splitting in traffic flowing at 30 MPH or less
** Motorcyclist lane-splitting at no more than 10 MPH over traffic speed
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