ITE Journal - April 2020 - 47

ƒ	 What local, state, and national policies are enacted to require
safety standards and reporting.

Technology Safety Strategies for an HAV Future
Strategies focused on moderating speed and reaction time in HAVs
would result in tangible safety benefits. These strategies could
also offer a compelling, systemic safety alternative, especially for
challenging roadway types, such as multimodal arterials that serve
high volumes of higher-speed vehicles often alongside VRUs.
Reaction time thresholds. HAVs programmed and regulated to
operate with a reaction time of 2.5 seconds or less would improve
safety outcomes compared to the average human driver. This
requirement could be tracked through performance reporting.
Absent regulation of HAV speeds, optimizing reaction times could
improve brake reaction distance and moderate risk faced by VRUs,
at a minimum.
Speed regulation. Another safety-related opportunity is
the standardization of speed limits for HAVs. HAVs can be
programmed to not exceed a speed threshold (i.e., posted speed
limit), regardless of a roadway's design speed, which would
reduce the risk posed by these vehicles to VRUs. HAVs can also
be programmed to travel at a specified margin below the posted
speed limit in adverse conditions, such as when visibility is low,
when reduced pavement friction precludes safe operation at the
posted speed limit, in environments with high pedestrian and
bicyclist activity, or near specific populations such as communities
of older adults. Implementing these strategies would require HAVs
to use information provided by roadway infrastructure (i.e., a
vehicle-to-infrastructure [V2I] environment) or their own vision,
sensor, and/or mapping systems to detect posted speed limits and
other environmental elements.19 It is still unclear how human
drivers in a mixed fleet might interact with HAVs, and average fleet
speeds could slow down if HAVs cannot exceed certain speeds, or
human drivers react by speeding to overtake slower moving HAVs.20

Street Safety Strategies for an HAV Future
Several built environment factors and considerations could help
mitigate safety risks posed by HAVs, particularly in environments
with VRUs, and are discussed below. Many of these factors would
also help improve safety for all road users, both today and in an
HAV future.
Speed Reduction Design Countermeasures. In addition to
regulating HAV speeds and reaction times, many existing speed
reduction strategies can and should continue to be implemented in
an HAV future. This is especially relevant as a portion of the vehicle
fleet will remain human-operated for many years. ITE has identified
speed management countermeasures as part of its Safe Systems
work today that will continue to be relevant with HAVs. These
strategies include measures to separate roadway users in space and

time, increase attentiveness and awareness, reduce speeds, and
reduce impact forces (i.e., cycle tracks and protected intersections,
pedestrian scrambles, road diets, and traffic calming measures).6
Technology applications related to speed management such as speed
feedback, variable speed limits, and automated speed enforcement
will also continue to be important.
Pedestrian Scale Lighting. Pedestrian scale lighting on
sidewalks and near crosswalks illuminates people walking/biking
for approaching motorists. Enhanced visibility improves the safety
of these crossings and the security and comfort of VRUs. To the
extent HAVs continue to use cameras as part of their detection
systems, lighting can help these vehicles detect VRUs. Adaptive
lighting with occupancy sensors and/or crossing warning devices
also offer an opportunity to provide infrastructure-based cues to
HAVs. Pedestrian scale lighting will also be important with regard
to equity, to offset biases HAV detection software may have with
respect to darker skin tones.21
Shared Streets vs. Protected Facilities. In settings with low
vehicle volumes and high VRU activity, shared streets may be an
attractive option if HAV speeds are software-controlled. However,
separated facilities for people walking/biking may be preferred
if vehicle speeds and volumes are higher to reduce exposure and
risk, and increase comfort and perception of safety for VRUs. In
recent years, separated facilities such as protected bike lanes and
protected intersections have gained traction as strategies to make
non-motorized modes safer, and more comfortable and attractive
for people of different ages and abilities. Protected facilities may
be even more important and effective in an HAV future, especially
to address potential safety issues related to poor detection of
people walking/biking, or comfort levels of people walking/biking
next to HAVs.16
Roadway Design, Materials, and Quick Build. In order to
operate safely across contexts, HAVs must be able to detect many
elements of the roadway environment. This means street elements
must be designed, built, and maintained in a way that's legible
to HAVs. This will impact cities' responsibility for maintaining
traffic control devices as well as attention to proper implementation of temporary traffic controls during construction. Similarly,
roadway legibility should be considered for quick build projects
and experimental treatments, which often allow complete streets
and safety-related projects to be installed more quickly using
lower-cost materials. HAV developers will need to collaborate with
transportation engineers to ensure legibility across a variety of
street design elements.
Transition Period Considerations. For all of these
strategies, it's important to consider that a fully automated
transportation system will develop slowly over time, if at all.
Some researchers predict that it will take until the 2050s for
AVs to constitute the majority of the operating fleet, and they
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