Thanks, traffic engineers.
“Installed under inappropriate conditions, a traffic signal is ineffective, inefficient, and a potential danger to motorists and pedestrians. Signals that are installed when no legitimate need exists often generate an increase in vehicle stops, traffic delays, fuel consumption, traffic accidents, and motorist disrespect for other traffic signals.”
On its web site, the Arizona Department of Transportation puts it even more bluntly:
“Traffic signals should be used only where lesser forms of control have proven ineffective, since signals almost always create more ‘overall intersection delay.’
If this awkward fact is apparent even to many traffic engineers, why do so many cities relentlessly continue to install more, bigger, and costlier traffic signals, often in locations that see barely a trickle of traffic?
Traffic engineers claim that they install signals to satisfy public demand, but common sense would tell you that most users of public roads--pedestrians included--are far from anxious to see even more signals impeding their movement. The noisy few who do clamor for more signals--usually under the banner of greater safety--are in for a surprise. Contrary to standard dogma, intersections with signals are generally no safer than those without, and in fact may even be more dangerous. Again, the Arizona DOT:
Graph comparing traffic fatalities at intersections with
a) traffic signals, b) signage, and (c) no controls at all.
Purple represents urban areas, maroon rural ones.
Compare traffic fatalities for signalized intersections
(first column) versus no controls at all (last column).
Source: U.S. Department of Transportation, 2007.
“While many people realize that traffic signals can reduce the number of angle collisions at an intersection, few realize that signals can also cause an increase in other types of accidents (it has been well documented that other types of accidents, notably rear-end collisions, usually increase when a signal is installed)...When there is no angle accident problem at an intersection...the installation of traffic signals can actually cause a deterioration in the overall safety at the intersection.”
Furthermore, Arizona’s DOT states:
“Because of the widespread (public) belief that traffic signals offer the solution to all intersection traffic control and accident problems, a number of signals have been installed nationwide where no legitimate operational warrant exists. Traffic records clearly show the attitudes and misunderstandings which sometimes lead to unjustified installations should be resisted.”
Yet not all traffic departments are so enlightened. Many are too deeply invested in all that complex and expensive signal hardware to offer simpler solutions even when they exist. For their part, signal manufacturers want to sell more of their product, not less, and they put considerable effort into convincing traffic engineers that more is always better. These two forces along will guarantee that redundant signal installations will continue unless the public demands simpler, cheaper, and more effective solutions.
Next time, we’ll look at a few such options--including replacing signals with nothing at all.