196｜Practice

Traffic safety and traffic enforcement

1. Background and goals
In 2012, the number of traffic accidents in Japan decreased for the eighth consecutive year to around
660,000. These accidents resulted in 4,411 fatalities, a reduction to approximately 30% of the peak in
1970. Although the downward trend in injuries continues, this year there have already been 820,000
people involved in traffic accidents, so accident prevention remains a significant problem. In particular,
there is a need for further efforts to eradicate fatal accidents due to drunk driving.
In the past, traffic enforcement efforts have had some level of success in preventing traffic accidents.
However, there seems to be no end to drivers who do not obey traffic rules. Cracking down on traffic
violations and strengthening penalties can resort in a short-term reduction of traffic accidents, but theytend to return to their previous levels with the passage of time.
This study aims to provide a quantitative measure of the effect of traffic enforcement on reducing
traffic accidents, and examines possible measures.
1-1. Research viewpoint and method
The embodiment of traffic enforcement has regional characteristics. For example, in large metropolitan
areas there are often efforts to control parking violations and vehicle access violations, both of whichmost frequently occur in densely populated areas. By contrast, in less densely populated rural areas,
efforts tend to be directed toward speed limit enforcement. There are also seasonal variations, such as
speed limit enforcement being more concentrated during the summer in regions that receive heavy
snow in winter. We therefore performed an analysis from the viewpoint of the regional characteristics ofviolators and violation enforcement.

2. Research content
2-1. Relation between traffic enforcement and traffic accidents
This section discusses whether traffic enforcement is effective in reducing traffic accidents. To give anexample, a relational diagram is presented showing the number of traffic enforcement incidents per day
and the number of traffic accidents per 1 million population in Tochigi Prefecture (Fig. 1). There werevery few traffic enforcement incidents (e.g., 100 incidents per day or less) on days such as the New Year’sProject Leader: Akinori Morimoto
Professor, Faculty of Science and Engineering, Waseda University

Traffic safety and traffic enforcement｜197

Number of traffic accidents (accidents/day)holidays when little traffic was on
the roads, and there were few traffic accidents on such days. Becauseof the existence of such atypicaldays, simply determining the correl at ion co ef f icient b et we en
enforcement and accidents would
likely not give a clear relation.
However, we also found atendency for the maximal numberof traffic accidents to decrease as

Average number of traffic incidents per day: 408
Average number of traffic accidents per day: 5290

Decreased upper bound (95th percentile)

80
7060

Average value

50
4030

0100

200300400500

600

700

800

9001000

1100

Number of traffic incidents per 1 million population (incidents/day)Figure 1. Relation between number of traffic enforcement incidents
and number of accidents in Tochigi Prefecture

the number traffic enforcement
incidents increases. The relational

diagram clearly shows that the upper bound (95th percentile) on the number of traffic accidents isreduced as the number of traffic enforcement incidents increases. This tendency was the same in Okinawa Prefecture and Akita Prefecture. These results suggest that traffic enforcement has the effect ofdecreasing the number of frequent traffic accidents.
2-2. Violation history of first parties in traffic accidents
Next, the focus is turned to first parties in traffic accidents—the pedestrian or driver of the vehicle whobear the greatest responsibility for the accident—and the first party’s history of past violations isconsidered.
Figure 2 shows of theNumber of violations
256 or more
413(%)
types of traffic violations for25
which the first parties in acciApproximately 23% of first parties in accidents had at leastdents occurring in 2009 were20
one violations for speeding in the previous five years
cited during the five-year period15

2004–2009. The violation histories show that 64% of male and
45% of female first parties had

105

some type of traffic violation on
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Figure 2. Violation history of first parties in accidents for the previous
five years

record from the previous fiveyears. Compared with secondparties, the first parties had ahigher violation rate for all typesof violations. This seems to indicate that the driving etiquette ofdrivers who bear primary

responsibility for accidents is worse than that of others involved in the accidents.

198｜Practice2-3. Regional trends in violations and their causes
To better understand theregional characteristics ofserious traffic violations, we
examined cities and prefectures with particularly highSignificantly higher

Average: 6.12%

Significantly lower
Shimane: 13.84%

rates of repeated willful violations, such as ignoring traffic
signals, speeding, and drunk
driving (Fig. 3). Particularly
notable were ignored traffic
lights in Osaka and drunk
driving rates in Okinawa. We

Hokkaido: 12.62%

Osaka: 16.22%

Ignoring traffic signal(3 or more)
Speeding(3 or more)
Drunk driving(2 or more)（％）

High drunk driving arrest rate
Okinawa: 1.13%

14.724 ave＋3σ〜
11.857 ave＋2σ〜
8.990 ave＋σ〜
6.123 ave〜
3.256 ave−σ〜0.389 ave−2σ〜

Figure 3. Percentage of repeated violations by first parties in traffic accidents

discussed the latter finding
with the Okinawa prefectural
police, who gave the following reasons for the high rates of drunk driving:• Okinawan drinking culture: starting to drink at late hours, the popularity of awamori (a local
beverage with a particularly high alcohol content), and the custom of passing drinks around.
• High reliance on automobiles because of lacking public transportation infrastructure and theprevalence of parking lots at drinking establishments.
To cope with this situation, efforts to combat drunk driving are concentrated between 2:00 and 6:00
a.m., when most accidents due to driving under the influence of alcohol occur. Moreover, since about
five years ago, early-morning operations have been conducted to prevent driving with an alcohol
hangover.
Such drunk driving enforcement efforts require significant time, and in recent years have becomeinefficient. There are limits to how much effort can be exerted, so ways to further reduce accidents is a
topic requiring further study.
2-4. Planning efforts based on numbers of traffic accidents and violations
As a simple method for investigating the effect of traffic enforcement, we created a plot showing thenumber of traffic accidents and number of traffic enforcement incidents.
Figure 4 shows the relation between the number of traffic accidents and the number of traffic
enforcement incidents by police station jurisdiction for individual town areas. The area covered isdivided into four zones (1–4), based on the average number of citations issued and average number oftraffic accidents.
Zone 3 has a low number of both citations and accidents. We therefore consider this area to besatisfactorily maintaining the status quo. Zone 4 has many citations and few traffic accidents. Areas

in this Zone wheretraffic enforcement(Incidents)

is considered excessive may there-100

in areas where accident suppression
is considered necessary, traffic enforcement efforts

120
Traffic accidents

fore require policy revisions, and140②806040Average number of citations

Traffic safety and traffic enforcement｜199①④③200050

100

Number of incidents

Average number of accidents

150200 (Incidents)
Utsunomiya City traffic citation data for 2005

Arranged by category①Improvements of traffic citations②Strengthened focus on enforcement③Maintaining current enforcement④Maintaining current enforcement

Figure 4. Example measures based on number of traffic accidents and number of incidents

may need to becontinued. Zone 1 has a many traffic citations but also many traffic accidents. Traffic enforcement efforts should continue in this area, but policies should also include consideration of other traffic safetymeasures such as improvement of the traffic environment. Finally, there were more traffic accidents
in zone 2 than in the other areas but the number of citations was below average. This likely indicates aneed to focus on strengthening traffic enforcement in this area.

3. Conclusions
This project performed a scientific investigation of the relation between traffic enforcement and traffic
accidents on the basis of a summary of statistical data from the results of previous research. The results
indicate that the relation between traffic accidents and traffic enforcement is strongly associated with
regional characteristics, and that investigations should be performed on a regional basis.
The following is a summary of our major findings.
• Traffic enforcement has the effect of decrease the occurrence of frequent traffic accidents.
• First parties in traffic accidents are typically poor drivers with a history of repeated traffic
violations.
• Repeated violations tend to be most common for drivers aged 25–34 years and to decreasebeyond that age range.
• Traffic enforcement varies according to the conditions of individual cities and prefectures, andpolicies best suited to each locale are required.

4. Future outlook
Connecting the results of this research to a reduction in the number of accidents in actual society will
fundamentally require consideration of measures on a regional basis. In 2013, we published Kotsu tori­
shimari handobukku (the Handbook for Traffic Enforcement) to promote traffic enforcement that iseffective for suppressing accidents. We hope this work will lead to efforts in accordance with the actual
regional situation surrounding traffic accidents.