ITE Journal - April 2020 - 45

Number of pedestrian deaths

6000
15

5000

4000
10
3000

2000

5

1000

0

2000

2002

2004

2006

2008

2010

2012

2014

2016

Pedestrian deaths per million population

20

7000

0

Year
Number of pedestrian deaths

- Rate of pedestrian deaths (per 1,000,000 population)

Figure 1. Traffic-related pedestrian fatalities over time.3 Source: NHTSA
One of the most significant factors influencing the frequency
and severity of collisions is vehicle speed, which directly affects the
amount of kinetic energy transferred during a collision. The rise
in speed-related VRU fatalities has prompted many transportation
agencies to enact strategies to counter this trend. One such effort is
Vision Zero, which is a "strategy to eliminate all traffic fatalities and
severe injuries while increasing safe, healthy, equitable mobility for
all."4 Vision Zero takes a Safe Systems approach that "acknowledges
that people make mistakes and focuses on influencing system-wide
practices, policies, and designs to lessen the severity of crashes."5, 6, 7
As a result, many safety approaches, from roadway planning and
design to policy-making, are being re-focused to encourage safer,
more context-appropriate travel speeds, and to build "safety nets"
into street design to prevent or mitigate crashes.8
In combination with street design and built environment
strategies, targeting HAV speed and reaction time-how quickly
HAV software can detect and react to an object in the roadway-
will be important safety strategies in the future. To date, there have
been few scholarly publications examining how the regulation of
HAV speed or reaction time might factor into safety outcomes.
Even as technology advances to help reduce risks related to human
errors, a Safe Systems approach that considers the physics behind
vehicle design, speed, and reaction time is of critical importance

to reducing the number and severity of collisions, especially those
involving VRUs.6 This article focuses on how an approach to
regulate HAV vehicle speed and reaction time could help reduce
collision frequency and severity in an HAV future. HAVs have the
potential to bolster current policies and programs that support
Safe Systems, but transportation professionals need to work with
policymakers and vehicle companies toward policy, legislation, and
vehicle and software design that create safe HAVs and safe streets to
operate them on.9 This article discusses both technology-side and
street design strategies that may be necessary in an HAV future.
While VRUs are the focus of the discussion presented here, speed
and reaction time are important considerations for all collisions
and roadway users, which give the findings broader relevance for
multimodal safety.

Speeds, Reaction Time, and Roadway Safety
As shown in Figure 2, the likelihood of a VRU fatality increases
substantially the faster a motor vehicle is moving at the time of
collision. Because higher vehicle speeds are linked to an increased
likelihood of fatality or serious injury for VRUs during a collision,
multimodal arterials-characterized by high volumes of fast-moving
vehicles traveling alongside VRUs-have become one of the most
challenging roadway types to improve safety outcomes.10
w w w .i t e.or g

Apri l 2020

45


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ITE Journal - April 2020

Table of Contents for the Digital Edition of ITE Journal - April 2020

ITE Journal - April 2020 - Cover1
ITE Journal - April 2020 - Cover2
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ITE Journal - April 2020 - Cover3
ITE Journal - April 2020 - Cover4
https://www.nxtbook.com/ygsreprints/ITE/ITE_July2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_June2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_May2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_April2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_March2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_February2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_January2020
https://www.nxtbook.com/ygsreprints/ITE/ITE_December2019
https://www.nxtbook.com/ygsreprints/ITE/G110939_ITE_November2019
https://www.nxtbook.com/ygsreprints/ITE/G110110_ITE_October2019
https://www.nxtbook.com/ygsreprints/ITE/G110109_ITE_September2019
https://www.nxtbook.com/ygsreprints/ITE/G108559_ITE_August2019
https://www.nxtbook.com/ygsreprints/ITE/G108250_ITE_July2019
https://www.nxtbook.com/ygsreprints/ITE/G107225_ITE_June2019
https://www.nxtbook.com/ygsreprints/ITE/G104039_ITE_May2019
https://www.nxtbook.com/ygsreprints/ITE/G104038_ITE_April2019
https://www.nxtbook.com/ygsreprints/ITE/G104036_ITE_March2019
https://www.nxtbook.com/ygsreprints/ITE/G103582_ITE_February2019
https://www.nxtbook.com/ygsreprints/ITE/G102868_ITE_January2019
https://www.nxtbook.com/ygsreprints/ITE/G100155_ITE_December2018
https://www.nxtbook.com/ygsreprints/ITE/G100154_ITE_November2018
https://www.nxtbook.com/ygsreprints/ITE/G99495_ITE_October2018
https://www.nxtbook.com/ygsreprints/ITE/G98028_ITE_September2018
https://www.nxtbook.com/ygsreprints/ITE/G97366_ITE_August2018
https://www.nxtbook.com/ygsreprints/ITE/G96287_ITE_July2018
https://www.nxtbook.com/ygsreprints/ITE/G94315_ITE_June2018
https://www.nxtbook.com/ygsreprints/ITE/G93877_ITE_May2018
https://www.nxtbook.com/ygsreprints/ITE/G93065_ITE_Apr2018
https://www.nxtbook.com/ygsreprints/ITE/G91484_ITE_Mar2018
https://www.nxtbook.com/ygsreprints/ITE/G89434_ITE_Feb2018
https://www.nxtbook.com/ygsreprints/ITE/G86608_ITE_Jan2018
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