Are not higher travel speeds good for the economy?

Written by LS Friedman
Wednesday, 29 July 2009
The financial benefit from higher travel speeds is, at best, limited to an immediate return for a segment of U.S. commerce, but ignores the long-term and comprehensive costs that result from higher gas consumption, increased air pollutants, more lives lost, and the burden of lost years of productivity.  A prudent speed policy can have a direct impact on our growing dependence on foreign oil and climate change, in addition to saving lives.  Furthermore, America functioned perfectly fine for the 20 years under the National Maximum Speed Law with excellent economic growth.

Are not higher travel speeds safer?

Written by LS Friedman
Wednesday, 29 July 2009
There is no quality evidence that driving faster is safer.  There are reports that indicate that higher travel speeds are associated with fewer crashes, severe injuries and deaths. These reports use very simple scientific designs and do not adequately control for trend or other events that may be associated with the observations.  In the scientific peer-reviewed literature the published evidence clearly shows that increases in travel speeds lead to more deaths and decreases in travel speeds result in fewer deaths.  This is basic Newtonian physics. 

Can I/We distribute your manuscript within our organization or with our colleagues?

Written by LS Friedman
Wednesday, 29 July 2009
We do not own the copyright to this publication.  The American Journal of Public Health does.  Therefore, you can not post this manuscript on a website or mass distribute it.  If you have colleagues that would like a copy, please contact us directly.

Important notice: Production error in manuscript:

The headings for both tables are incorrect.  The dates should read 1990-2005, not 1987-1988.  The production office is correcting this error. 

Do you control for changes in population and number of drivers?

Written by LS Friedman
Wednesday, 29 July 2009
We control for the two more important variables - vehicle miles traveled and number of vehicles on the road.  Number of registered drivers or population growth does not necessarily mean more cars or more travel.  Vehicle miles traveled attempts to directly control for exposure – driving on the road.  However, more vehicle miles traveled and number of vehicles also leads eventually to congestion.  Therefore, we integrate "congestion" into the variables by dividing them by miles of public roads.  This gives us density estimates.  There was a curvilinear relationship between fatalities and both density measures.  In other words, fatalities increase with exposure and vehicle density until the roads become so dense (congested) that travel speeds begin to decline.  No one gets killed in a traffic jam.   We also control for other important factors, most important the variance between and within states.  Wyoming is not the same as New York.

Do you or any of the authors have any affiliations with companies that can profit from such a study (e.g. speed camera companies)?

Written by LS Friedman
Wednesday, 29 July 2009
None of the authors have any conflicts of interest in regards to this study.  No funding was provided or solicited to complete the study. None of the authors have ever been employed by any corporation that develops, sells or distributes materials that are related to speed control, speed monitoring, or traffic safety.  All the authors are employees of not-for-profit academic Universities.  All the authors certify that we have no affiliation with any company that may profit from our findings in the form of employment, grant/research, consultant, honoraria, speakers bureau, stock ownership or options, expert testimony, pending worker's compensation claim, pending legal case, patents received or pending royalties. 

Is not reducing the likelihood of a crash in the first place still the best method of reducing fatalities?

Written by LS Friedman
Wednesday, 29 July 2009
Better training in avoidance can be far more effective; witness any auto race, for instance. Though a crash at Talladega or Daytona is spectacular for the forces involved it is still a rare event considering the speeds involved?

Yes reducing the risk of being involved in a crash is one of the most important ways of reducing injury and death on roads.  NASCAR and all forms of high speed racing are great examples of using the best protective engineering for reducing the transfer of energy to the occupant.  The authors of this study would love to see some of these safety designs introduced to passenger vehicles including the engineering technology used for framing the vehicle and exemplary use of restraints and head protection.  None of the authors are advocating speed limits of 10 mph. 

A great case for the efficacy of improved safety equipment is the fact that we observed substantial declines in fatalities in the 10 states that did not make any major changes to their speed limits.  Had there not been systematic changes in the other states -- increased energy throughout the road system -- it is very likely they too would have shown substantial reductions in fatalities.  We believe that there needs to be a multi-faceted approach to dealing with the near 40,000 deaths that occur each year on U.S. roads.  Speed control needs to be a central part of the debate and policy, in addition to all the other important factors that reduce crashes, divert energy from occupants and improve post-crash care.

What about cell phones, bad drivers, texting, and distractions?

Written by LS Friedman
Wednesday, 29 July 2009
It is important to not confuse the factors that increase the risk of a crash with those that increase the severity of injury.  A simple way to think of it, is that there are pre-crash risk factors, in-crash risk factors and post-crash risk factors.  Miles traveled, number of cars, congestion, weather, road design, cell phones, drunk driving, etc are pre-crash factors that are related to risk of being involved in a crash.  Travel speed is an in-crash factor that is related to severity of injury and risk of death.  Travel speed does not necessarily increase the risk of being in a crash.  This is basic Newtonian physics (mass*acceleration = Force; or kinetic energy = 1/2*mass*velocity squared).   The object of in-crash protective devices (seat belts, air bags, crash zones) is to reduce the energy transferred to the occupants during a crash.  However, as you introduce more energy into the crash phase (through speed or mass or both) you increase the energy transferred to an occupant.  Traumatic injury is the result of the transfer of energy to the human body.  Therefore, more speed means more energy transferred to the occupants, which means more severe injuries and risk of death.    This does not mean that higher travel speeds necessarily results in more crashes, but that the increase in energy during the in-crash phase leads to more severe injuries/risk of death.

What are the implications of your findings?

Written by LS Friedman
Wednesday, 29 July 2009
Speed kills.  The repeal of the National Maximum Speed Law is an example of a policy that can have a direct life or death impact on its citizens.  There is a general accepted risk and callousness towards fatalities in motor vehicle crashes.  However, our study clearly shows that policy can directly result in more deaths.  The inverse is true as well -- a well guided policy can lead to reduction in deaths on roads.

What are the key findings of your study?

Written by LS Friedman
Wednesday, 29 July 2009
We estimate that between 1995 and 2005, approximately 12,500 people died as a result of repealing the National Maximum Speed Law.  In the 10 states that essentially did not change their posted speed limits, we observed a substantial decline in fatalities and injuries in fatal crashes.  Therefore, had the other states not raised their speed limits we expect that similar declines would have been observed.  In our study we control for differences between the states, vehicle miles traveled, congestion, and posted speed limits.

What are your recommendations?

Written by LS Friedman
Wednesday, 29 July 2009
The 10-year experiment of deregulated speed limits in the U.S. is a clear example of a failed policy.   The repeal of the National Maximum Speed Law and its aftermath show that policy decisions that appear harmless can have long-term repercussions.   Managing travel speeds on U.S. highways should be a principle priority of the Department of Transportation.   A national speed management policy needs to be implemented and should entail at its core (1) reduced maximum speed limits back to 55 mph and (2) the development of wide spread speed camera networks to curb individuals who continue to drive too fast.   A system wide reduction in speed will immediately reduce the key pathogen – kinetic energy – and therefore, result in fewer fatalities. However, we do not advocate a singular policy of speed reduction, but a broad approach to improve road safety through the implementation of programs that reduce crashes, divert energy from occupants and improve post-crash care.

Won’t a speed limit reduction waste everyone’s time?

Written by LS Friedman
Wednesday, 29 July 2009
The notion that it is desirable to continue a policy that increases the risk of death to save 3 minutes on the average commute is absurd (20 miles; 55 vs. 65; no congestion).  The authors of this study believe there is an ethical and moral imperative to improve road safety and achieve the goals of Vision Zero (no fatalities).  Reducing speed limits and improving enforcement of travel speeds will result in an immediate reduction in road deaths.