The Reference Energy Mean Emission Level (REMEL) database is an inventory of different vehicle pass-by noise levels that is the basis for the FHWA Traffic Noise Model (TNM) analysis software. It is 25 years old and in need of updating. Internal combustion engines have become more efficient, overall vehicle technology has evolved, truck exhaust stack noise has decreased, truck exhaust stack locations are changing, and electric and hybrid vehicles are entering the vehicle population. Newer noise measurement technology has also evolved, and it can be applied to locate and quantify noise generators on a moving vehicle. The old REMEL database positions and distributes a significant amount of vehicle noise energy at 5 and 12 feet above the pavement. Recent NCHRP research shows that most vehicle noise energy is at the tire/pavement interface or only 3.3 feet above the pavement. The 5- and 12-foot energy distributions used in TNM strongly biases analysis toward tall, and expensive, sound walls, and it underestimates noise reductions that shorter berms and concrete safety barriers can provide. The old REMEL database also underestimates the acoustic variation caused by different pavements and how the different pavements influence roadside noise levels. This outdated REMEL database adversely impacts sound wall analysis and limits available design options. Tall sound walls are about $2M/mile and shorter less-expensive noise barriers would provide state departments of transportation (DOTs) more design flexibility in mitigating highway noise impacts. Quieter pavement strategies keep money in the road, not in barriers. More design options would help DOTs better address noise-related inequity issues also.
This research will use the two new highway acoustic measurement technologies of OBSI and acoustic beamforming, in combination with the old measurement process – SPL, to develop a new REMEL database for the current vehicle fleet. The five basic acoustic vehicle classifications (heavy truck, medium trucks, passenger cars, buses, and motorcycles) will be re-measured and updated. The beamforming will show the relative amount and location of vehicle noise in the vehicle profile and OBSI will more accurately measure the pavement acoustics and how it correlates to roadside noise. These two new measurement processes will be combined with the old-school, roadside SPL measurements. Based on previous NCHRP research, this will reduce noise contributions from the old-and-outdated 5 ft and 12 ft vehicle sub-source positions currently used in TNM, and more accurately distribute the noise energy in the vehicle profile.
Highway noise is always a top environmental concern with the public on any highway project. Updating and improving the 25-year-old vehicle noise REMEL database will improve the accuracy of traffic noise analysis. This will provide state DOTs with more design options and flexibility to mitigate the environmental impacts of highway noise. The use of shorter, less expensive noise barriers and quieter pavement strategies will also help address equity related issues and would save a significant amount of taxpayer dollars.
The final product will be an updated vehicle noise REMEL database based on the current vehicle fleet and measured with both old and new acoustic measurement technologies that will better quantify and position the vehicle noise sub-sources: mechanical, exhaust, tire/pavement. A preliminary analysis will also be included with the database to discuss the differences between the new REMEL database and the older REMEL data.
Pass-by noise levels will be measured for different acoustically isolated individual vehicles operating under different conditions using SPL, OBSI, and beamforming acoustic measurement technology. The measurement matrix would include different vehicle types, different speeds (10 to 80 mph), cruising, acceleration/deceleration, flexible and rigid pavements, and different road grades.
The REMEL database should be thoroughly documented and the data made available in an open-source format for immediate use by state DOT engineers and noise analysts and other third-party noise simulation software vendors. To better accommodate future updates and improve accuracy and limit computational adjustment factors, the REMELs will be based on source measurements and referenced relative to the vehicle position in the traffic lane and will not be based on measurements taken at a distant receptor position. Most noise barrier design is performed on federally funded public works transportation projects and the REMEL database directly impacts structural noise barrier design. All stages and phases of the development of the REMEL database will be managed and reviewed by an experienced and responsible registered engineer. Implementation into the FHWA TNM software is not included in this research.