ITE Journal - May 2020 - 30

safe behaviors should be developed. For example, the Texas
A&M Transportation Institute is working on a program that
provide rewards for users who do not access their phone
during a trip. In-vehicle systems that help prevent use of cell
phones while the vehicle is moving to minimize distraction.
3.	 Decrease impairment by all users. The use of alcohol
and drugs-prescription or illicit-is known to cause fatal
and serious crashes. Increased enforcement alone will not
prevent users from getting behind the wheel when they
should not. Data linkage is one promising strategy, which
pulls together driving records, adjudication, and citations to
show the community and law enforcement who should not
be behind the wheel.

Accommodating Human Injury Intolerance

Seattle Department of Transportation

In the Safe System framework, accommodating human injury
intolerance is the second key element. Two principles are at play in
helping humans survive a crash and limit their injuries: reducing
speed, and limiting impact forces. Reducing speed in the presence
of vulnerable users is a key Safe System strategy.
Reduce Speeds. The laws of physics dictate that greater harm
will occur at high speed, and that, the greater the mass of a vehicle
the more harm that it will inflict on others. Reducing speed in the
presence of vulnerable road users is a key Safe System strategy.
In urban areas this strategy starts will reassessing speed limits
and moving toward the use of context-specific target speeds in
lieu of the 85th percentile speed for speed limit setting. The use of
traditional or automated enforcement is also a key tool to support
lower speeds. However, lower speed limits and enforcement along

Figure 3. Vehicle impact speed and a pedestrian's chances of survival.
30

May 2020

i te j o urnal

are unlikely to result in sustained decreases without accompanying
changes in the infrastructure. These changes can include narrowing
the width of the traveled lanes and introducing horizontal
alignment changes to reduce free flow speeds, using traffic calming
treatments, or implementing traffic signal timing changes the
minimize high speed flow.
Reduce Impact Forces. A variety of methods can increase crash
survivability by reducing impact forces. Traditionally, this has been
accomplished by protecting the user inside a vehicle by improving
the crashworthiness of the vehicle, advocating the use of restraint
systems and through mitigation devices such as air bags. Similarly,
roadside hardware has been designed to improve crashworthiness
through the use of guardrails and crash cushions to protect drivers
from hazards and breakaway devices to lessen impact forces.
The angle of a vehicle also has an influence on crash impact. At
90 degrees, there is a large amount of kinetic energy transferred
between the vehicle and the colliding object. That kinetic energy
drops off as the angle decreases, so transportation professionals
can reduce the severity of a crash by employing designs that lessen
speed and angle. The roundabout is one of the most common and
impactful ways to reduce both these elements.
This framework represents starting point for the development
of a Safe System toolbox that can aid practitioners in the implementation of design and operational treatments that will save lives and
reduce serious injuries. Additional development of this framework
is needed to fully incorporate lessons learned from other countries
that are applicable to the United States. The development and trial
of novel or innovative techniques needs to be encouraged and
expanded so there are more tools available to address the wide



ITE Journal - May 2020

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

ITE Journal - May 2020 - Cover1
ITE Journal - May 2020 - Cover2
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https://www.nxtbook.com/ygsreprints/ITE/ITE_Mar2021
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