As some American cities are attempting to reduce the number of car accident fatalities, under the umbrella of Vision Zero, the growing topic is one of traffic enforcement. Streetsblog has long documented many instances in which the police treats any case in which a car runs over a pedestrian as a no-fault accident, even when the driver was committing such traffic violations as driving on the sidewalk. In addition to enforcement, there’s emphasis on reducing the speed limit in urban areas, from 30 to 20 miles per hour, based on past campaigns in Europe, where speeds were reduced from 50 km/h to 30. Unfortunately, street design for lower speeds and greater traffic safety has taken a back seat. This is not the best way to improve street safety, and is not the standard practice in the countries that have reduced car accident rates the most successfully, namely the UK and the Scandinavian countries.
On high-speed roads, one of the most important causes of fatal accidents is the combination of driver fatigue and sleepiness. For some studies on this problem, see here, here, and here. The second link in particular brings up the problem of monotony: if a road presents fewer stimuli to the driver, the driver is more likely to become less vigilant, increasing the probability of an accident. One study goes on and shows that higher speed actually increases monotony, since drivers have less time to register such stimuli as other cars on the road, but this was obtained in controlled conditions, and its literature review says that most studies find no effect of speed. I emphasize that this does not mean that lower speed limits are ineffective: there’s evidence that reducing highway speed limit does reduce accident rates, with multiple studies collected in a Guardian article, and lower accident rates in France since the state installed an extensive system of speed cameras.
But while speed limit reductions offer useful safety benefits, it is important to design the roads to be slower, and not just tell drivers to go slower. Road monotony is especially common in the United States; per the second study again,
While comparing self-reported driving fatigue in the US and Norway, Sagberg (1999) suggests that the higher prevalence of self reported drowsy driving found in the US may be due to differences in road geometry, design and environment, as well as exposure. He argues that the risk of falling asleep is higher on straight, monotonous roads in situations of low traffic, where boredom is likely to occur. This type of roads is more common in the US than in Norway.
The studies I have consulted look primarily at highways and rural roads; I have not found comparable literature on urban roads, except one study that, in a controlled simulation, shows that drivers are better at gauging their own alertness levels on urban arterials than on rural roads. That said, urban arterials share many design traits that lead to monotony, especially in the United States and Canada:
- They are usually straight, forming a grid rather than taking haphazard routes originating from premodern or early-industrial roads.
- They are wide: 4-6 lanes at a minimum, often with a median. Lanes are likely to be wide, closer to 3.7 meters than the more typical urban 3 meters.
- Development on them usually does not form a strong enclosure, but instead commercial developments are only 1-2 stories, with setbacks and front and side parking lots.
Such roads are called stroads in the language of Charles Marohn, who focuses on issues of their auto-centric, pedestrian-hostile nature. Based on the studies about monotony, I would add that even ignoring pedestrians entirely, they are less safe than slower roads, which prime drivers to be more alert and to speed less. It is better to design roads to have more frequent stimuli: trees, sidewalks with pedestrians, commercial development, residential development to the extent people are willing to live on top of a busy road.
Regarding lane width, one study finds that roads are the safest when lanes are 3-3.2 meters wide, because of the effects of wider lanes on driver speeds. A CityLab article on the same subject from two years ago includes references to several studies that argue that wide lanes offer no safety benefit for drivers, but are hostile to pedestrians and cyclists.
This approach, of reducing speed via road design rather than enforcement, is common in Scandinavia. Stockholm has a few urban freeways, but few arterials in the center, and many of those arterials have seen changes giving away space from cars to public transit and pedestrians. Thus, Götgatan is partly pedestrianized, and Odengatan has center bus lanes and only one moving car lane in each direction; the most important of Stockholm’s streets, Sveavägen, has several moving car lanes in each direction, but is flanked on both sides by medium-rise buildings without setbacks, and speeds are rarely high.
When enforcement happens, the great successes, for example in France under the Sarkozy administration, involve automation. Red light cameras have a long history and are controversial, and in France, Sarkozy lowered the speed limits on many roads and stepped up speed camera enforcement. The UK has extensive camera enforcement as well. Human enforcement exists, but is less common than speed cameras. Thus, the two main policy planks Vision Zero should fight for in the US are,
- Road redesign: narrower lanes, wider sidewalks, trees, and dedicated bus and bike lanes in order to reduce the number of car lanes as well as provide more room for alternatives. Zoning laws that mandate front setbacks should be repealed, and ideally so should commercial height limits on arterials. In central cities, some road segments should be closed off to cars, if the intensity of urban activities can fill the space with pedestrians.
- Lower speed limits in the cities, enforced by cameras; fines should be high enough to have some deterrent effect, but not so high that they will drive low-income drivers bankrupt.
It is especially important to come up with solutions that do not rely on extensive human enforcement in the US, because of its longstanding problem with police brutality and racism. The expression “driving while black” is common in the US, due to bias the police in the US (and Canada) exhibits against black people. In Europe, even when bias against certain minorities is as bad as in the US, overall police brutality levels are lower in the US by factors ranging from 20 to 100 (see for example data here). In my Twitter feed, black American urbanists express reluctance to so much as call the police on nonviolent crime, fearing that cops would treat them as suspects even if they are the victims. When it comes to urban traffic safety – and so far, Vision Zero in the US is an urban movement – this is compounded by the fact that blacks and other minorities are overrepresented in the cities.
This means that, in the special conditions of US policing, it’s crucial to prevent Vision Zero from becoming yet another pretext for Driving While Black arrests. As it happens, it does not require large changes from best practices in Europe, because those best practices do not involve extensive contact between traffic police and drivers.
Recall last year’s post by Adonia Lugo, accusing Vision Zero of copying policy from Northern Europe and not from low-income American minority communities. As I said a year ago, Adonia is wrong – first in her belief that foreign knowledge is less important than local US knowledge, and second in her accusation that US Vision Zero advocates copy European solutions too much. To the contrary, what I see is that the tone among US street safety advocates overfocuses on punitive enforcement of drivers who violate the speed limit or break other law. Adapting a problem that in Europe is solved predominantly with street design and technology (speed cameras don’t notice the driver’s skin color), they instead call for more policing, perhaps because mainstream (i.e. white) American culture is used to accepting excessive police presence.