Frequently asked questions

While there are many factors that may have a potential to influence traffic noise, traffic volume is the predominant factor. With that said, traffic is at its loudest when the traffic operates at Level of Service C. This is the condition of a stable flow of vehicles, at or near free flow in a lane, but lane changing and maneuverability may be challenging. During Level of Service C at 70 mph, there are approximately 1,500 vehicles per hour and per lane. When traffic volumes increase beyond Level of Service C, vehicle speeds decrease and lower the noise levels.

The correlation between traffic volumes and noise levels is a helpful tool for ADOT to determine the future noise levels based on current conditions. Generally, doubling the traffic may increase noise levels by 3 decibels (dBA), and an increase of 20- 25 percent in traffic volume may increase noise levels by 1 dBA.

ADOT utilizes data collected from the permanent automatic traffic recorders, an integral part of ADOT’s traffic data management system. That data will provide hourly/daily traffic patterns which, in turn, will provide the periods that the freeway operates at or close to “level of service c” – the highest level of traffic noise based on traffic volume and travel speeds. ADOT will continue to evaluate data and determine 2.5-hour windows of time - in the morning and afternoon - with similar traffic volumes when testing would occur. As previously noted, this will occur when average daily traffic counts return to more typical conditions.

Measurements will be taken at representative locations along the South Mountain Freeway; that is, residential neighborhoods, parks, schools and similar locations. Measurements are typically restricted to exterior areas of frequent human use. Interior measurements are taken only when there are no outside activities, such as at churches, hospitals and libraries. Measurements are typically taken in one of three exterior locations: (1) at or near the highway right-of-way line; (2) at or near buildings in residential areas; and (3) at an area between the right-of-way line and the building where frequent human activity occurs, such as a patio or the yard of a home. ADOT will cover all noise-sensitive areas throughout the 22-mile corridor, within the project limits, at areas within approximately 1,000 feet from the freeway. A map with the location, date and time of the field noise measurements will be posted on the project website at southmountainfreeway.com when it is confirmed.

Because of the COVID-19 pandemic, average daily traffic volumes throughout Maricopa county are lower than usual. Taking noise measurements during this pandemic is not representative of typical traffic noise levels. ADOT is planning to resume field noise testing in late summer/early fall 2020 and in late February/early March 2021. Beyond that, ADOT will continue testing noise levels throughout the 22-mile corridor regularly in select locations. Schedules are subject to change because of the pandemic and other unforeseen situations. Updated information will be posted on the project website at southmountainfreeway.com when it is confirmed.

“Fully operational” means that the monitoring systems and overall conditions on the freeway are conducive to continuous, uninterrupted, and free-flow traffic operations, and that the traffic volumes are aligned with the levels predicted by the Maricopa Association of Governments (MAG) travel demand model for the year 2020.

ADOT is conducting noise measurements in compliance with the Final Environmental Impact Statement (FEIS) for the South Mountain Freeway. Further, ADOT will evaluate the common noise environment within the project area after the freeway is “fully operational.”

The price tag of modern roundabouts versus traditional traffic-control methods can vary. Demographics, geography and environmental elements all make a difference when engineers, communities, and city and state planners begin to consider how to move traffic from one street to another.

Sometimes the financial cost of right-of-way acquisition is higher than the cost of traffic signal construction, and sometimes it is not a factor. For example, though modern roundabouts do not require traffic-light electricity, the maintenance of landscaping or public art can be a cost. However, the reduction in fatal, injury and pedestrian crashes can reduce other costs, including car insurance premiums, health insurance premiums, and physical and emotional trauma. When safety factors go up, the cost to society goes down.

While it depends on the number of pedestrians and vehicles, in many instances, a modern roundabout can be safer for pedestrians than a traffic signal. Pedestrian crossing is reduced to two simple crossings of one-way traffic that is proceeding at relatively slow speeds. Pedestrian safety is improved further by the a pedestrian crosswalk sign placed right where a vehicle enters a modern roundabout. Even with this precaution, it is recommended that pedestrians always use caution and designated crosswalks.

Auto-pedestrian crash rates are usually lower at modern roundabouts than traffic signals. Also pedestrian injuries that do occur tend to be less serious because of the relatively low speeds demanded by modern roundabouts.

Properly designed modern roundabouts safely accommodate bicycles. Because vehicles are traveling at 15-25 mph, bicyclists can negotiate this traffic mode like a car.

In most situations, a modern roundabout can handle higher traffic volumes with less delay than traffic signals because motorists do not stop for traffic lights. A two-lane roundabout will handle the same capacity as other major intersections in the Valley, and a three-lane roundabout handles up to 6,000 vehicles per hour.

First, slow down! You should approach a modern roundabout at no more than 25 mph. Most importantly, do not merge. Always yield to traffic in circulation when entering a modern roundabout. Do not attempt to cut in front of traffic, but wait for a safe gap. The drivers already in the roundabout have the right of way.