SAVING LIVES BY KEEPING DRIVERS FOCUSED Noise from Centerline Rumble Strips

On just one stretch of 2-lane highway in rural Minnesota from 1986-2011 Overal head-on crash statistics found in the reports 25posted PEOPLE here: https://dps.mn.gov/divisions/ots/reports- WERE KILLED IN HEAD-ON CRASHES statistics/Pages/crash-facts.aspx

this averages out to one person killed per YEAR

What is a rumble strip? How do rumble strips help? Rumble Strips are indentations in the The “rumble” alerts motorists that are road surface – usually on the shoulders straying from the travel lane, prompting or along the centerline – that cause them to correct their steering and stay in noise and vibration when a vehicle their lane or on the road. Centerline rumble drives over them. strips reduce crashes significantly: Drivers who are: • distracted • speeding 44% • tired • inexperienced 39% 9% 12% can unintentionally drift over the centerline and cause crashes. Total Fatal & Total Fatal & Injury Crashes Injury Head-On Head-On } Crashes Crashes Crashes Based on multi-state data from NCHRP Report 641, 2009.

“Toward Zero Deaths” Initiative About Rumble Strips The Toward Zero Deaths (TZD) approach is based on the belief that Some may find the intermittent noise made even one traffic-related death on our roads is unacceptable. The when a car drives on a rumble strip annoying. MnDOT TZD mission of zero traffic fatalities has identified centerline However, that same noise may prevent injury or rumbles as an effective way to reduce crashes. save a life.

While our primary objective is the safety ON AVERAGE, MORE THAN of drivers and passengers on Minnesota THE ONLY People roadways, MnDOT takes concerns about noise ACCEPTABLE impacts seriously. are killed NUMBER IS AND To evaluate the noise impacts made by the 60 600 centerline rumble strips on communities along injured highways, MnDOT works closely with traffic noise in head-on type crashes experts to monitor, measure, and analyze the EVERY YEAR noise made by traffic passing over rumble strips. on Minnesota roads and highways 0 How do we measure and regulate noise?

COMPARISON OF How do we measure noise? NOISE LEVELS The human range of hearing extends from approximately 3 -140 decibels. decibels The scale to the left shows various noise levels in a real-world context.

110 Noise levels in outdoor areas can fluctuate widely over time. Noise experts B-747-200 use mathematical models to analyze the noise level data that they gather. Takeoff* These analyses account for noise level variations due to factors like 100 ambient noise, the distance traveled by the noise, multiple noise sources, atmospheric conditions, etc. Food blender The example graph below shows how monitored noise levels can vary at 3 feet 90 substantially in an outdoor setting.

Large truck Noisy urban 80 daytime

Small car 70 Normal speech at 3 feet

Noise Levels Ambient noise (wind, 60 leaves rustling, etc.)

Dishwasher in Time next room 50 How is noise regulated? Because outdoor noise levels can fluctuate widely, the Minnesota Quiet urban Pollution Control Agency uses two noise metrics to set limits on outdoor 40 nightime noise levels: L10 and L50.

represents the noise level exceeded for 10% of the hour L10 30 (i.e., noise levels can’t exceed 65 decibels for more than 6 minutes Quiet rural of any hour during the day, or 55 decibels at night). nightime represents the noise level exceeded for 50% of the hour 20 L50 (i.e., noise levels can’t exceed 60 decibels for more than 30 minutes of any hour during the day, or 50 decibels at night). Threshold of human

10 hearing * As measured along the takeoff path 2 miles from the overflight end of the runway the of end overflight the from miles 2 path takeoff the along measured As * Noise Limits for Residential Land Uses

Time of Day L10 L50 Changes in noise levels of less than <3 decibels 3 decibels are not typically detectable DAYTIME by the average human ear. decibels decibels (7am – 10pm) 65 60 An increase of 5 decibels is +5 decibels generally noticeable by anyone. NIGHTTIME 55 decibels 50 decibels A 10-decibel increase is usually felt (10pm – 7am) +10 decibels to be “twice as loud” Source: Minnesota Pollution Control Agency (MPCA). 2008. A Guide to Noise Control in Minnesota: Acoustical Properties, Measurement, Analysis, and Regulation. MnDOT’s rumble strip noise study

Collecting noise data Rumble Strip and Monitoring Locations Rumble strip noise events are intermittent and short Along a Roadway in duration. In order to account for the sporadic nature of rumble strip noise as well as highway noise and The diagram to the left environmental variables, we measured rumble strip noise shows placement of both using two methods: long-term and pass-by monitoring locations during Method 1: an actual study along a LONG-TERM MEASUREMENTS stretch of roadway in rural Minnesota with centerline Sound level meters were placed for one week at a rumble strips installed. location along the road. The meters measured all sound The placement of the that occured day and night for 7 consecutive days. monitoring locations, as well as the distance of each monitoring location from the Method 2: centerline of the roadway, PASS-BY MEASUREMENTS varies based on land use in Measured noise from a specific car driving at a known the study area. speed in a controlled setting. The test measured the car: • Driving on the road with no rumble strips • Driving on the rumble strip like a drifting car would • Driving on the rumble strip like a passing car would Map Key

To gather reliable noise data along a highway, we placed Rumble Strip Location sound level meters at multiple locations to measure noise Represents ~30 miles. Distance will vary for each project levels for a week. Pass-by We also conducted pass-by tests at multiple locations monitoring location along the highway. The sound level meters were placed Long-term as close as 25-feet from the centerline for the pass-by monitoring location measurements, and as far as 900-feet from the centerline for the long-term measurements (see below).

Typical Cross-Section Along Highway Edge of Edge of right-of-way Centerline right-of-way Sound 12 ft. 8–10 ft. 18–28 ft. level meter Shoulder Lane Lane Shoulder 25–900 ft. Right-of-way: 38–50 ft. from centerline Rumble Strip Noise Study Results

Hourly L10 and L50 at a residence 60 feet from roadway

L daytime noise L 70 - 10 10 limit (65 decibels) What do these 60 - L nighttime noise results mean? 10 50 -

Decibels limit (55 decibels) Noise from traffic 40 - driving on rumble strips is distinctly 30 - Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8 different from typical traffic noise. The results from the long- L 70 - 50 L50 daytime noise term measurements 60 - limit (60 decibels) show that rumble strip 50 - L50 nighttime noise noise does not cause a Decibels limit (50 decibels) substantial increase in 40 -

the L10 and L50 values. 30 - Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8

Rumble Strip Noise Levels

Modeled Rumble Strip Noise (single rumble-strip event) Level Distance from road . . These modeled noise levels . each illustrate a single . rumble strip event at varying . distances. They are based . upon actual roadway noise . data. .

Decibels Individual Vehicle Noise (with no rumble strip events) Level Distance from road Represents a single vehicle driving at 55 MPH on a roadway 50 ft. with no rumble strip events.

Total Noise (with intermittent rumble strip events)

Level Distance from road These levels represent the total average noise measured at 130 ft. residences, including background 900 ft. and traffic noise, and occasional rumble strip events. Frequency (Hz)

Have questions? Contact the project team: Primary contact: Bradley Estochen, Traffic Safety Engineer (Minnesota Department of Transportation) Email: [email protected] | Phone: (651) 234-7011 More information: Rumble strips: www.dot.state.mn.us/trafficeng/safety/rumble Toward Zero Deaths: www.minnesotatzd.org