Researcher Guangqing Chi of the Department of Sociology and Rural Studies at South Dakota State University looked at the correlation between gas prices and traffic safety. In a study examining crash data in Minnesota from 1998 to 2007, Chi found that a 20-cent drop in gas prices resulted in 15 more fatalities a year. Conversely, he found that a 20-cent increase would bring a decrease of 15 deaths annually.
The study also found that as gas prices rise, the crash rate per million miles traveled dropped in urban and rural areas. It found higher gasoline prices also have significant effects in reducing property damage and injury crashes.
In another study using data from Alabama and Mississippi, Chi found higher gas prices had the biggest effect on teens. With their lower incomes, teens are discouraged from driving by high gas prices and that reduces their crash rate. That makes the roads safer for other drivers, he said.
When fuel prices skyrocketed to more than $4 a gallon in 2008, many drivers drove less frequently and perhaps less aggressively, which reduced their chances of having a crash, the study said.
The bottom line is that when gas prices go up, “we suspect that people drive more carefully,” Chi said.
In the constant exhortations to pedestrians around cars and trains, we hear “Safety is a shared responsibility“. This of course is true. Many crashes are the product of a chain of failures. The driver was too fast for conditions. The driver did not pay attention. The pedestrian did not pay attention. Someone else did not pay attention and braked sharply, and someone behind them swerved because they were following too close and hit a third person. And so on. Yet authorities are often quick to blame the victim, rather than the system design.
The more you hear the exhortation, the less effective it becomes (diminishing returns set in), much like the security threat warnings of the Bush Administration, telling us at the airport we were at threat level orange, constantly.
People are imperfect. They feel they have better things to be doing then looking out for lurking dangers around every corner. They did not evolve to operate in a city with multi-ton machines operating at speeds faster than the fastest land animals. They see meaningless signs and signals and learn to ignore them. Breaking traffic and pedestrian laws may be illegal, but it is hardly immoral – we don’t feel guilty when we conscientiously don’t allow ourselves to be governed by degrading light bulbs implemented by unthinking bureaucracies.
Designs for systems that involve people should consider human imperfection. Ideally systems are forgiving of human error. Light rail trains, e.g, are much more dangerous than buses. (Cars are too). They are far less tolerant of imperfection, as they can neither brake quickly (due to mass) nor swerve (due to tracks), and are more deadly on impact (again due to mass).
There are two good strategies for multi-modal travel within a finite space:
keep them separated and
mix them slowly
(The third strategy: mix them quickly will lead to tragedy as long as people are making decisions, rather than machines.)
The “keep them separated” strategy is why safety on interstate highways is much better than other streets. High speed vehicles are interacting with other high speed vehicles, but low speed vehicles are prohibited. It is far from perfect, but better than the previous alternative. So much so that when speed limits were raised in the 1980s, overall safety went up as drivers were attracted off much more dangerous roads onto the interstate, which was only marginally more dangerous with the higher speed limit, and now less likely to result in a speeding ticket. Security theater that deters people from flying and encourages them to drive is more dangerous than the original threat.
Newer subway systems (such as the shuttle at MSP airport between the terminal and the LRT station/parking ramps), have glass barriers preventing people from accidentally falling on the track. Despite running one train every 90 seconds or so for over 10 years, I have not heard of any incidents with this system.
The Minneapolis-St. Paul region has chosen, for the most part, not to build grade separated transit systems. They are certainly more expensive, even if more beneficial (safer and faster). That leaves the strategy of “mix them slowly.”
Proponent of shared spaces, the late Hans Monderman has a famous quote “When you treat people like idiots, they’ll behave like idiots.”
As the song goes “Signs, signs, everywhere signs”. Each sign and signal degrades the effectiveness of all the others. Monderman went for a sign and signal-free approach, using design to guide people and vehicles through town centers. In this scheme pavements give people the guidance they need.
While peer-reviewed evaluations of shared spaces have been limited, Kaparias et al. from Imperial College, evaluating Exhibition Road, say: “The results suggest that pedestrians feel most comfortable in shared space under conditions which ensure their presence is clear to other road users – these conditions include low vehicular traffic, high pedestrian traffic, good lighting and pedestrian-only facilities. Conversely, the presence of many pedestrians and, in particular, children and elderly, makes drivers feel uneasy and, therefore, enhances their alertness.” Subsequent research by the team finds “The results of the comparative analysis indicated a general decrease in traffic conflict rates as a result of the redesign but also highlighted specific issues that may require additional analysis”
Karndacharuk et al. write: “A comparative analysis of the data after implementation highlights the importance of the active frontage in enabling a lower (vehicular) speed environment in relation to the number of pedestrians within the shared space.”
In short, design matters. Over-engineering can be as great or even greater sin than under-engineering. The best design is not necessarily more gadgets, instructions, rat runs, prohibitions on actions, closing of desire lines, or other devices constraining people from their intuitions.
Rather it is running with and shaping travelers natural instincts, so the environment is not chafing but accommodating. Safety is a shared responsibility, and those who diminish the effectiveness of safety tools such as signs and signals by their misuse and excessive exhortations which loosely spend people’s scarce attention are culpable as well.
The following appeared across the email transom. The source is unknown. The forwarder stated:
One of my Internet Buddies sent it claiming it to be an Isreali invention. Who knows. Maybe it’s a joke, but none-the-less it appears to be a great idea, unless of course people swerve out of their lane and cause an accident!
Update: part of an ad campaign by Pioneer Suspension.
Hi Dr. Levinson, I searched for the message that was written on the road in the pictures and came up with this:
“Light rail trains empirically kill more people than buses,” said David Levinson, a civil engineering professor and transportation studies expert.
Metro Transit spokesman John Siqveland said the Green and Blue Lines were built with safety in mind and that the Green Line will generally run slower since it will travel through more densely populated areas.
The vast majority of light-rail and streetcar systems around the country run on street level, Siqveland said.
Metro Transit has two train routes and 125 bus routes. Of the 81 million rides Metro Transit gave last year, 86 percent of riders use buses and 14 percent use trains.
Since the Blue Line opened in June 2004, the agency’s buses have had 6,979 incidents, which resulted in five deaths. Like the light rail, the majority of collisions involved motor vehicles. Of the 145 bus incidents involving pedestrians, four were fatal.
“Buses serve a lot more people and run a lot more miles … but have fewer fatalities,” Levinson said. “The [fatality] rates are obviously much higher for light-rail trains. Still, it’s a lot safer than driving a car.”
The 11-mile light-rail route connecting downtown Minneapolis to downtown St. Paul is decades in the making and cost $957 million.
“It’s been built, so it’s too late. It’s an at-grade light-rail facility — there’s nothing we can do about it without spending another billion dollars,” Levinson said. “We don’t operate in this world to maximize safety and only safety; we have trade-offs.””
The low-friction nature of train travel makes it efficient, but it also makes stopping a problem, said Stephen Zitzow, Minnesota Traffic Observatory laboratory manager.
Each train weighs about 300,000 pounds, and bringing one to a complete stop from 55 mph takes the length of two football fields. At 20 mph, it takes 81 feet, Siqveland said.
“It doesn’t have the option to swerve out of the way of someone in the way,” Zitzow said. “The difference here is that most vehicles can maneuver much more than a light rail, which is stuck.”
Central Corridor project spokeswoman Laura Baenen said the Green Line will begin running before the Major League Baseball All-Star game at Target Field in July.
Baenen said the Metropolitan Council has taken many safety considerations, including creating a pedestrian mall and using posters and community educators.
Baenen said a street-level light-rail track is less costly than an underground or elevated one, which was “prohibitively expensive.”
Siqveland said part of the Metro Transit safety campaign will have links to its website posted at every train stop.
When asked if he’d visit the website, graduate student Hill said he most likely wouldn’t.
“If I am an example,” he said, “[other students] probably will not.”
See also this (presented at TRB) (which is a bit dated), still I think it is largely accurate. Another interesting tidbit is that urban autos kill relatively few people (on a per mile basis). More auto deaths (on a per capital, per mile, etc. basis) are rural.
Most empirical studies on the role of information in markets analyze policies that reduce asymmetries in the information that market participants possess, often suggesting that the policies improve welfare. We exploit the introduction of pedestrian countdown signals – timers that indicate when traffic lights will change – to evaluate a policy that increases the information that all market participants possess. We find that although countdown signals reduce the number of pedestrians struck by automobiles, they increase the number of collisions between automobiles. We also find that countdown signals caused more collisions overall. The findings imply welfare gains can be attained by revealing the information to pedestrians and hiding it from drivers. We conclude that policies which increase asymmetries in information can improve welfare.
“Daylight Savings Time is an archaic practice in our modern society.
The original reasons for the policies are no longer applicable, and the most cited reason for keeping DST (energy savings) has never been shown to be true.
Some industries still like DST (like sporting equipment retailers), but there are many more who dislike the changed hours (like television).
The real issue, however is not the later hours or extra sunlight. Studies have shown that changing the clocks is responsible for health problems (including increased heart attack and vehicular accident risks) and leads to hundreds of thousands of hours of lost productivity in workplaces across the country. Also: It’s really annoying.
We should either eliminate DST or make it the year-round standard time for the whole country.”
While our results on the traffic safety consequences are mixed (DST reduces crash rates but increases traffic) it nets that DST enhances safety. Still, I tend to agree with the petition, we could achieve the benefits by having a fixed adjustment year round. And if people want to switch behaviors relative to the clock, good for them. Me, I would eliminate timezones too, and have one global time, so I wouldn’t have to go to work until 14:00 GMT and could sleep in every day.
Huang, Arthur and David Levinson (2010) The Effects of Daylight Saving Time on Vehicle Crashes in Minnesota Journal of Safety Research 41 513-520.
The jokes about dreadful female drivers can officially take a back seat.
For the first time ever, more women than men have driver’s licenses nationwide. This gender gap reversal means safer roads and less pollution.
That’s according to the University of Michigan’s Transportation Research Institute, which says that in 2010, 105 million women held licenses, compared with 104 million men. Women are more likely to purchase “smaller, safer and more fuel-efficient vehicles” and “drive less and tend to have a lower fatality rate per distance driven,” said Michael Sivak, the study’s co-author.
The stereotype, however, has been a joke as long as women have been driving.
“It wasn’t true and I don’t think people find it funny anymore,” said David Levinson, a professor in the Department of Civil Engineering at the University of Minnesota.“Statistics have long shown that the average woman is a slightly safer driver than the average man.”
One interesting policy implication is that as gas prices go up, average insurance rates should go down, since risk is dropping. Whether it goes down by cohort, or just overall as the shares of various cohorts traveling changes, is unclear.
I had a media inquiry a year ago on “Why we become such bad drivers when it snows”, I didn’t take it, but the question is interesting in a sense. Unlike the rain in southern California, it always snows in Central Minnesota, so this is a recurring question.
Several things happen when it snows:
1. Roads are slipperier and require longer braking distances. People recognize that roads are slipperier and give increased spacing (following headway in the jargon) to the car in front. Instead of following at a 2 second headway (remember the 2 second rule from Driver’s Ed), they may follow at a 3 second headway. Since there are 3600 seconds in an hour, a 2 second headway implies 1800 vehicles per hour (traffic engineers will note of course that capacities per lane on freeways are often greater than this in good conditions, implying a shorter than 2 second headway). A three second headway implies a service flow or capacity (Qmax) of 1200 vehicles per hour. If the underlying demand (those who want to use the bottleneck at that time) remains unchanged at 1800 vph (say it snowed surprisingly in the middle of the day), then instead of serving 1800 cars, a bottleneck would serve only 1200 in an hour. This implies a queue 600 cars long. That is non-trivial.
2. Roads are slipperier. People recognize that roads are slipperier and drive slower to reduce braking distances, especially on roads which curve.
Kyte et al. “The effects of poor weather conditions on free-flow speed on a rural Interstate freeway are considered. It was found that free-flow speed is affected by pavement conditions, visibility, and wind speeds. It is also suggested that poor weather conditions occur with some degree of frequency in a number of U.S. cities and that the effects of poor weather should be considered in such cases as part of capacity and level-of-service analyses.”
3. Roads are slipperier. People insufficiently recognize that roads are slipperier and instead of giving increased spacing choose to crash into the vehicle in front of them. This temporarily reduces capacity to zero as the drivers sort out the situation.
Khattak and Knaap “significant increase was observed when winter snow event injury and noninjury crash rates (crashes per million vehicle kilometers) were compared with equivalent winter nonsnow event injury and noninjury crash rates. The data were then analyzed for injury occurrence. Results of a logit model indicated that crash injury occurrence on Interstate highways in Iowa depended on traffic, road geometry, and number of vehicles involved in a crash. Another finding from the logit model was that crashes during snow events were less injurious compared with equivalent nonsnow event crashes. Snow event–specific crash data were then analyzed to study the effects of snow event elements (e.g., snowfall intensity) on injury occurrence in vehicular crashes.”
4. Snow does in fact reduce demand. People choose not to go out when it snows. Arthur Huang and I conducted some research on Minnesota travel patterns statewide and found these elasticities (so if it snows, there is a 5.9% reduction in demand and 63.9% increase in crashes in the 3am to 9am time period). The reduction in demand seems to be less than the reduction in capacity, so queueing increases on roads at or near capacity in the absence of snow.
9pm – 12am
A. Huang, D. Levinson / Journal of Safety Research 41 (2010) 513–520
Others have found significant results as well:
Datla and Sharma “The commuter roads experience lowest reductions in traffic volume due to cold (up to 14%) while the recreational roads experience highest reduction (up to 31%). Impact of cold on off-peak hours (-10% to -15%) is generally higher than peak hours (-6% to -10%) for commuter roads and an opposite pattern is observed for recreational roads (peak hour reductions of 30–58% and off-peak hour reductions of 18–30%). A clear indication of reduction in traffic volume due to snow is also observed for all types of highways.”
So I wouldn’t say we become bad drivers. We are bad drivers, we just reveal it when the environment changes to the unexpected.
(This presents one more argument for robot cars. They can’t overcome the physics of braking distance or eliminate congestion, but they can in principle better assess road conditions and be less likely to crash.)