ST. GEORGE — As the community continues to grow, traffic increases and new traffic signals sprout up along the way, including those on Foremaster Drive, 3000 East and River Road over the last 18 months.
Traffic volume is just one the factors road planners examine when considering whether a new traffic control signal is warranted at a particular location. However, popular opinion is not necessarily one of those factors.
Cameron Cutler, public works director for the city of St. George, told St. George News that residents often tell him that a traffic signal needs to go at this or that intersection for various reasons.
“Some people say, ‘I have to wait for x-amount of time at these intersections before I can go,’” Cutler said. “A lot of the time people call me up and say, ‘Hey, this is a really bad intersection – there are a lot of near-misses here.’
“They don’t like to hear that near-misses don’t warrant a traffic signal.”
According to the Mike on Traffic blog, which covers traffic engineering topics, the three primary points of data used to evaluate the need for traffic signals are the layout of the intersection, speed limits and traffic volumes. Other factors include crash data, how close other traffic signals are, as well as proximity to schools, parks and other high pedestrian areas.
The type of road is another factor, Cutler said, whether the road is a major arterial roadway or side street.
Traffic signals – which cost $200,000-$300,000 – are not always warranted and road planners will go with the installation of an all-way stop, a roundabout or another method of traffic control that is considered a better fit for the area, he said.
“There are just some traffic patterns that don’t always warrant a signal.”
Traffic engineers primarily evaluate the data rather than popular opinion on where a signal should be located, Cutler said.
“There’s a fine line to when it comes to satisfying people.”
Planning for traffic signals really has two parts, Cutler said.
The first part involves planning for the city’s growth and determining where new signals may need to go. Those future signal sites are marked on the city’s transportation master plan.
Estimated traffic volume for future intersections can be used to justify signals in areas currently not considered viable for a traffic signal.
One such spot is 3000 East and 2000 South where new schools are located and continuing development is slated to occur. To get motorists accustomed to the incoming traffic signal at that intersection, all-way stop signs at 3000 East and 2000 South were installed.
The second part of traffic signal planning involves Federal Highway Administration guidelines known as “traffic control signal warrants.”
According to the Manual of Uniform Traffic Control Devices, a warrant is “a threshold condition based upon average or normal conditions that, if found to be satisfied as part of an engineering study, shall result in analysis of other traffic conditions or factors to determine whether a traffic control device or other improvement is justified.”
There are nine warrants that go into qualifying an intersection for the traffic control signal, eight of which the city of St. George considers in its planning, Cutler said.
- Warrant 1, eight-hour vehicular volume.
- Warrant 2, four-hour vehicular volume.
- Warrant 3, peak hour vehicular volume.
- Warrant 4, pedestrian volume.
- Warrant 5, school crossing.
- Warrant 6, coordinated signal system.
- Warrant 7, crash experience.
- Warrant 8, roadway network.
- Warrant 9, intersection near a grade crossing (train crossing).
As may have already been guessed, Warrant 9 is the one St. George road planners ignore.
Warrants 1-3 deal with the amount of traffic during certain times of day and are determined through traffic studies.
Warrant 4 tends to deal more with large pedestrian traffic volumes like can be seen in places like Manhattan, according to a webinar from Spack Consulting, the consulting firm behind the Mike on Traffic blog.
Warrant 5, dealing with school crossings, is applicable where “schoolchildren cross the major street is (and) the principal reason to consider installing a traffic control signal,” according to the Manual of Uniform Traffic Control Devices.
Warrants 6 and 8 are related because they deal with maintaining the continuity of traffic flow. Warrant 6 considers the impacts the installation of a traffic signal may have on a traffic corridor, such as River Road or Riverside Drive. Warrant 8 looks at the overall traffic system and not just an individual intersection.
Along with factors indicating where traffic signals can be placed, the Manual of Uniform Traffic Control Devices also goes into detail on the spacing between signals to avoid overly disrupting traffic flow.
“If I go out and stick a traffic signal just anywhere, that could cause a lot of trouble,” Cutler said.
Traffic lights placed on major roadways don’t always benefit traffic flow on those roads as much as they do the side streets connected to them.
Warrant 7 entails crash data to be considered as justification for a traffic signal. The requirement for this, Cutler said, is five more or “correctable crashes” in an intersection per year over a span of three years.
A correctable crash is one that could be corrected by a light installation, such as a left turn. Rear-end collisions are not considered under Warrant 7.
Just because a light is installed at an intersection, it doesn’t necessarily mean that crashes will go down. Signaled intersections like 1000 East and St. George Boulevard, and Sunset Boulevard and Dixie Drive, still see a high-number of crashes over a year’s time.
While the Manual of Uniform Traffic Control Devices provides guidelines for traffic engineers to follow, the warrants may not be considered equal from city to city or state to state, such as Warrant 9 in relation to St. George.
Traffic signal installations can run between $200,000-$300,000.
St. George News reporter Joseph Witham contributed to this article.
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