San Joaquin Valley Air Pollution Control District June 25, 2013 

NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

APPENDIX D: 

NO2 Near-Road Monitoring Station Siting Requirements and Selection 

Process for the Bakersfield Core Based Statistical Area 

 
San Joaquin Valley Air Pollution Control District June 25, 2013 

NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

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D-i NO2 Near-Road Monitoring Station Siting Requirements 

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TABLE OF CONTENTS 

1. Introduction ................................................................................................................. 1

2. Site Selection Process ............................................................................................... 2

2.1 Traffic Count Data .................................................................................................. 2

2.1.1 AADT .............................................................................................................. 2

2.1.2 AADTT ............................................................................................................ 3

2.1.3 Fleet Mix.......................................................................................................... 3

2.1.4 Fleet Equivalent AADT .................................................................................... 3

2.1.5 Postmile .......................................................................................................... 3

2.1.6 Traffic Congestion ........................................................................................... 4

2.2 Physical Characteristics of Near-Road Sites ......................................................... 4

2.2.1 Roadway design or configuration and clear zones .......................................... 4

2.2.2 Roadside structures and vegetation ................................................................ 7

2.2.3 Terrain ............................................................................................................. 7

2.2.4 Meteorology .................................................................................................... 7

2.3 Spatial scales and population exposure ................................................................ 7

2.4 Safety .................................................................................................................... 8

3. Site Selections for Bakersfield CBSA ......................................................................... 8

3.1 Introduction ............................................................................................................ 8

3.2 Traffic Count Data .................................................................................................. 9

3.2.1 Road Segment Ranking .................................................................................. 9

3.2.2 The top 10 road segments ............................................................................ 10

3.2.2.1 Segment 1: Bakersfield, California Ave ............................................... 11

3.2.2.2 Segment 2: Bakersfield, Ming Ave ....................................................... 12

3.2.2.3 Segment 3: JCT RTE 58 East ............................................................. 12

3.2.2.4 Segment 4: Bakersfield, White Lane.................................................... 12

3.2.2.5 Segment 5: Buck Owens Blvd ............................................................. 12

3.2.2.7 Segment 7: Panama Lane ................................................................... 13

3.2.2.8 Segment 8: JCT. RTE. 99 North .......................................................... 14

3.2.2.9 Segment 9: Oil Junction ....................................................................... 15

3.2.2.10 Segment 10: Olive Drive .................................................................... 15

3.3 Meteorological Considerations............................................................................. 15

3.4 Terrain through Bakersfield CBSA ....................................................................... 16

3.5 Spatial scales and population exposure ............................................................. 17
San Joaquin Valley Air Pollution Control District June 25, 2013 

D-ii NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

3.6 Correspondence with property owners ................................................................ 18

4.0 Final Site Selection .................................................................................................. 18

Appendix A —Traffic Data Tables ................................................................................. 22

Appendix B—Site Details .............................................................................................. 24

Appendix C—Maps of Segments .................................................................................. 25

Segment 1 ................................................................................................................. 26

Segment 2 ................................................................................................................. 27

Segment 3 ................................................................................................................. 28

Segment 4 ................................................................................................................. 29

Segment 5 ................................................................................................................. 30

Segment 6 ................................................................................................................. 31

Segment 7 ................................................................................................................. 32

Segment 8 ................................................................................................................. 33

Segment 9 ................................................................................................................. 34

Segment 10 ............................................................................................................... 35

 
San Joaquin Valley Air Pollution Control District June 25, 2013 

D-iii NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

 TABLE OF FIGURES 

Figure 1: Above Grade Road ......................................................................................... 5

Figure 2: Below grade with up-slope .............................................................................. 5

Figure 3: At grade roadway ............................................................................................ 6

Figure 4: Junction, interchange, on-ramp, and off-ramp................................................. 6

Table 1: Kern County Top Road Segments by Fleet Equivalent AADT4 ..................... 10

Figures 5a and 5b: General location of the top 10 road segments in the Bakersfield 

CBSA. ........................................................................................................................... 11

Figure 6: A sample site in Segment 7 that was not pursued because it was on the 

windward side of the freeway. ....................................................................................... 14

Figures 7a through 7c: Wind Roses ............................................................................. 15

Figure 8a: Map of the Bakersfield Metropolitan Area .................................................... 17

Figure 8b: Map of the Interstate 5 – Freeway 99 JCT Area ........................................... 17

Figure 9: Final Section—2809 Unicorn Road ............................................................... 19

Figure 10: Selected site located at 2809 Unicorn Road in Segment 9 ......................... 20
San Joaquin Valley Air Pollution Control District June 25, 2013 

D-iv NO2 Near-Road Monitoring Station Siting Requirements 

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D-1 NO2 Near-Road Monitoring Station Siting Requirements 

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1. Introduction 

In 2010, the U.S. Environmental Protection Agency (EPA) established a new 1-hour 

standard and new minimum monitoring requirements for nitrogen dioxide (NO2). 

Additionally, EPA promulgated new NO2 monitoring network design requirements which 

consist of three distinct NO2 air monitoring networks. The first network is the near-road 

monitoring network which is aimed at capturing the higher NO2 concentrations that 

occur near roadways. The second network is the area-wide monitoring network which 

will represent NO2 concentrations characteristic of large neighborhood or urban areas. 

The third network, which is called the Regional Administrator Required Monitoring 

Network, requires Regional Administrators to work with states to site a network of 40 

NO2 monitors throughout the nation in locations aimed at protecting susceptible and 

vulnerable communities. 

The monitoring requirements for the first two monitoring networks mentioned above for 

the new NO2 1-hour standard are based upon the population of Core Based Statistical 

Areas (CBSAs) as well as the annual average daily traffic (AADT) counts. The intent of 

the NO2 near-road network is placing the monitoring stations near major roads where 

maximum hourly NO2 concentrations are expected. As noted in Section 4.3 of Appendix 

D of 40 CFR Part 58, one microscale near-road NO2 monitoring station is required in 

each CBSA with a population of 500,000 or more. Data such as traffic volumes, fleet 

mix, roadway design, traffic congestion patterns, and characteristics such as local 

terrain or topography, and meteorology are among the criteria that must be considered 

when determining areas which have the highest NO2 concentrations. Additionally, 

population exposure, near-road siting criteria, safety, surrounding land use, and other 

factors are also considered during the location selection process. NO2 monitors that are 

required under this new standard are to be operational by January 1, 2013; however 

EPA recently released a proposed rule that will move this date to January 1, 2017. To 

assist agencies with the siting selection process, EPA provided the Near-Road NO2

Monitoring Technical Assistance Document (TAD) which outlines recommendations and 

ideas on how to successfully meet the revised NO2 near-road monitoring requirements1. 

EPA requires air monitoring agencies to submit a report which describes the site 

selection process for each NO2 near-road monitoring station that will be established. 

The San Joaquin Valley Air Pollution District (District) is required to install four nearroad air monitoring stations, one in each of the following CBSAs: Stockton, Modesto, 

Fresno, and Bakersfield. Accordingly, a report of the site selection process will be 

submitted by the District for each of the aforementioned stations. 

With considerable assistance provided by the California Air Resources Board (CARB), 

the District carried out a detailed process of selecting a site for a near-road monitoring 

 

1

Near-Road NO2 Monitoring Technical Assistance Document (TAD) – A document that provides state and local air 

 agencies with recommendations and ideas on how to successfully implement near-road NO2 monitors in order to 

 meet the NO2 minimum monitoring requirements that were revised in 2010. 

 http://www.epa.gov/ttnamti1/files/nearroad/NearRoadTAD.pdf
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D-2 NO2 Near-Road Monitoring Station Siting Requirements 

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station in the Bakersfield CBSA. This report describes the site selection process 

conducted by the District and CARB for the purpose of establishing a new NO2 nearroad monitoring station. 

2. Site Selection Process

The District conducted a site selection process that involved assistance from the CARB 

in gathering traffic count data, and determining candidate road segments and the 

positive and negative attributes of each. Road design, and wind direction associated 

with each road segment were also considered during the process. Once the acceptable 

land parcels were decided upon, a lease was negotiated between the District and one of 

the property owners and the final site selection was made. In addition to following the 

guidance provided in the TAD, the District also considered PM2.5 so the site could 

potentially accommodate a PM2.5 monitor in the future. 

2.1 Traffic Count Data 

In order to determine the road segments that theoretically have the highest NO2 

concentrations, CARB and the District assessed all available traffic count data available 

from the California Department of Transportation (Caltrans) for Kern County. The data 

included AADT, Fleet mix, FE-AADT, and congestion data. Following the guidance 

found in the TAD, the District and CARB used FE-AADT to determine and rank the road 

segments. 

2.1.1 AADT 

Traffic counts represent AADT which is the total traffic volume for one year divided by 

the number of days in the year. AADT usually depicts the traffic volume along a given 

road segment. All traffic count figures listed include traffic in both directions. Ahead 

AADT typically refers to traffic north and east of a traffic count location, and Back AADT 

typically refers to traffic south and west of a traffic location. To avoid overlapping data, 

the Ahead AADT was used in the District’s site selection process. 

Caltrans typically collects traffic counts on freeways. The majority of continuous traffic 

count sampling is conducted by moving the electronic counting instruments from 

location to location throughout the state. Traffic counts are adjusted estimates of AADT 

which compensate for seasonal influence, weekly variation, and other variables. 

 
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D-3 NO2 Near-Road Monitoring Station Siting Requirements 

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2.1.2 AADTT 

Truck traffic is classified by the number of axles trucks have. For example, 11⁄2 -ton 

trucks with dual rear tires are included in the two-axle class but pickups and vans with 

only four tires are not. Annual average daily truck traffic (AADTT) is the total truck traffic 

volume for one year divided by the number of days in the year. Continuous truck count 

sampling consists of vehicle classification counts that are conducted throughout 

California. This program includes partial day and 24-hour counts on high volume, urban 

freeways, and 7-day counts on low volume, rural freeways. Truck counts are adjusted 

estimates of AADTT which compensate for seasonal influence, weekly variation, and 

other variables. 

2.1.3 Fleet Mix 

Fleet mix pertains to a specific count or percentage of the total volume of traffic and 

differentiates between light-duty (LD) vehicles and heavy-duty (HD) vehicles. 

Differences between LD and HD vehicles include the type of fuel they run on (gasoline 

vs. diesel), and the vehicle’s weight, length, or number of axles. NO2 emissions vary for 

all vehicles depending on vehicle type; load, speed, and freeway grade, however, diesel 

fueled HD vehicles typically emit far higher amounts of NO2 than do gasoline fueled LD 

vehicles. Fleet mix is important in determining where the emission differences occur. 

2.1.4 Fleet Equivalent AADT 

FE-AADT is a metric2 that accounts for total traffic volume and fleet mix in order to 

compare road segments, especially when the amount of total traffic volume and HD 

volume on those road segments varies. FE-AADT gives a better indication of estimated 

NO2 emissions than does AADT. The FE-AADT values shown in Table 1 below were 

determined using Ahead AADT and AADTT in the equation below: 

FE-AADT = (Ahead AADT – AADTT) + (AADTT*10) 

This equation gives truck traffic 10 times the weight of non-truck traffic in determining 

rank because the NO2 emissions are approximately 10 times as great as non-truck 

traffic. The segments with the highest levels of NO2 should be those with the greatest 

truck traffic. 

2.1.5 Postmile 

Caltrans has identified Postmile values as breakpoints on Freeways that usually 

increase from South to North or West to East depending on the direction the route 

follows within the county. Postmile values increase from the beginning of the route to 

the next county line and then start over. The total AADT values shown in the tables 

below apply to the freeway immediately ahead of the Postmile. 

 

2

For more information on the equation that defines FE-AADT, go to 

 http://www.epa.gov/ttnamti1/files/nearroad/NearRoadTAD.pdf.
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D-4 NO2 Near-Road Monitoring Station Siting Requirements 

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2.1.6 Traffic Congestion 

Traffic congestion can lead to stop-and-go traffic conditions and per-vehicle emissions 

may increase as a result. A notable and constant reduction in speed between two 

points on a freeway is defined as a bottleneck. The congestion values shown the tables 

below are annual vehicle hourly delay (AVHD) in thousand hours and represent the sum 

of the delay from the morning and evening peak periods and from the midday period. 

2.2 Physical Characteristics of Near-Road Sites 

The physical characteristics of candidate road segments must be considered in order to 

determine which segments are adequate for near-road monitor placement. The 

characteristics to be assessed and accounted for include roadway design, roadside 

structures and vegetation, terrain, and meteorology. 

2.2.1 Roadway design or configuration and clear zones 

Road design or configuration is important in determining acceptable locations for nearroad monitors because it can impact the dispersion and transport of pollutants. Road 

designs can be characterized as above-grade, below-grade, or at-grade. Additionally, 

road designs that contain features such as interchanges and toll plazas can influence 

vehicle acceleration and deceleration rates which in turn affect pollutant concentrations 

and plumes. 

Above-grade or elevated road configurations can be open or have solid fill material 

beneath them (see Figure 1). Roads that are open underneath are subject to wind from 

all directions, increased dispersion, turbulence, and dilution of the air as it flows over 

and under the road. These affects can cause pollutant concentrations to be lower 

downwind of the elevated roadway. Roads that are over solid fill material can have 

winds normal with the road and forces that keep the traffic plume near at the surface 

while others can cause the plume to loft above the ground when it meets the vertical 

filled material or wall beneath. 

 
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D-5 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

Figure 1: Above Grade Road 

Roads that are configured below-grade can have vertical or sloped walls that facilitate 

the funneling of air parallel to the road (see Figure 2). As the air streams through the 

corridor it can cause pollutant plumes to loft and be carried away as the air flows 

through, up, and out of the below-grade roadway. 

Figure 2: Below grade with up-slope 

 

Roadways that are generally at the same elevation as the immediate surrounding 

terrain are referred to as at-grade roadways (see Figure 3). Other than structures or 

obstacles near the roadside, at-grade roadways pose the least amount of impact on 

pollutant dispersion. As stated in the TAD, at-grade or near at-grade roads are the most 

desirable road configurations for siting near-road monitors. 

 
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D-6 NO2 Near-Road Monitoring Station Siting Requirements 

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Figure 3: At grade roadway 

As stated above, EPA requires that NO2 near-road monitoring stations be placed in 

areas representative of high NO2 levels. According to the TAD, road areas that go 

uphill or downhill, and roads that contain on-ramps and off-ramps, interchanges, or 

unique features such as toll plazas, and tunnel entrances and exits should not be 

considered for NO2 near-road monitor placement because they are designed for rapid 

vehicle accelerations and decelerations (see examples in Figure 4). These areas and 

road designs do not produce representative NO2 concentrations. The most suitable 

place to locate an NO2 near-road monitoring station is one that is at grade with 

immediate flat surrounding terrain. 

Figure 4: Junction, interchange, on-ramp, and off-ramp 
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D-7 NO2 Near-Road Monitoring Station Siting Requirements 

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Clear zones denote roadside areas that are available to drivers who need to pull over 

and stop safely or regain control if a vehicle leaves the road. Such zones extend from 

the road’s outside traffic edge to an obstacle further off the road. The roadway’s traffic 

volume, design speeds, and the slope of the terrain adjacent to and beneath the 

roadway are used to determine the width of the clear zone. Near-road monitoring 

stations are placed outside of clear zones. 

2.2.2 Roadside structures and vegetation 

Roadside structures such as sound walls or noise barriers can affect dispersion by 

blocking it or causing turbulence which can mix pollutants. Roadside structures can 

channel pollutants downwind and inhibit or reduce normal dispersion along the 

roadway. Vegetation can also affect pollutant transport and dispersion by mixing and 

diluting air as it blows through the branches and leaves of trees, and by blocking wind 

and slowing dispersion down. Additionally, pollutant concentrations in traffic plumes 

can decrease when particulate pollutants get deposited onto the surfaces of branches 

and leaves. Locations that are void of roadside structures and vegetation are therefore 

more acceptable for near-road monitor placement. 

2.2.3 Terrain 

Local terrain can affect dispersion and pollutant transport so it is important to have a 

good understanding of the large scale terrain features that characterize the air basin 

when considering locations for near-road monitor placement. For example, valleys may 

be more susceptible to high NO2 concentrations because the surrounding terrain and

temperature inversions tend to inhibit dispersion whereas open terrain areas allow for 

better air flow which can aid in lower pollutant concentrations. 

2.2.4 Meteorology 

The TAD states that evaluating historical meteorological data can be helpful in 

determining locations that may be directly impacted by traffic emissions from particular 

road segments due to local winds. Understanding the local meteorology can also 

indicate which side of a road segment may be more impacted by the traffic emissions. 

Research studies have shown that locations very close to the roadway on the downwind 

side of a given road segment can adequately capture peak pollutant concentrations. 

2.3 Spatial scales and population exposure 

40 CFR Part 58 Appendix D requires that the spatial scale of a NO2 near-road air 

monitoring site be classed as a microscale site. Microscale sites measure peak 

concentrations in an area with of a radius 100 meters. Concentrations decrease 

significantly as distance increases outside of this area. This being the case, EPA 

requires near-road monitoring stations to be placed as close as practicable but no 

further than 50 meters from the target road segment. Additionally, EPA requires that 

the sampling inlet be within 2 to 7 meters from the road’s surface. 
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D-8 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

As specified in 40 CFR Part 58 Appendix D, Section 4.3.2(a)(1), state and local air 

monitoring agencies shall consider the potential for population exposure when making 

their final near-road monitoring site selections when there are multiple acceptable sites 

in the same ranked segment. 

2.4 Safety 

As specified in the TAD, NO2 near-road monitoring stations must be safely sited for 

motorists traveling the roadway and for the monitoring station operators. The sites are 

required to be safely and legally accessible to station operators and pose no safety 

hazards to drivers as well as people walking or living nearby. In addition, some sites 

will require the installation of permanent safety barriers, such as guardrails. 

3. Site Selections for Bakersfield CBSA 

3.1 Introduction 

As stated in Section 2.0 above, the District started with traffic count data to select the 

freeway segments that were to be considered for a site. Meteorology, terrain, road 

structures, parcels with locations acceptable for building a site on, and landowner 

willingness to host a site on their property all played a role determining site 

selection. Since the segments were nearly continuous the District looked at them as a 

whole, focusing on finding acceptable locations. It quickly became apparent that the 

highest ranked segments in the urban core did not have any available land for 

constructing a site. These segments in central Bakersfield were typically above or 

below grade with sound walls which prevented placement of the site close enough to 

the edge of the freeway to capture peak values. In fact, the District found that there are 

only a few locations along the top ten segments that could meet all of EPA’s siting 

criteria. 

At this juncture, the District decided to contact all landowners of parcels with acceptable 

locations in the top ten segments and prioritize working with the landowners who 

responded positively within the highest ranked segments before moving further down 

the list. 

The District process in locating a NO2 near-road site can be summed as follows: 

• Rank all road segments 

• Determine the top 10 segments 

• Find locations were a site can be built (acceptable locations or parcels) 

o Take into account meteorology, structures, obstacles, grade, and other 

criteria. 

o Take into account near-road exposure. 

• Contact property owners by sending a letter 

• Contact those property owners that are willing to work with us starting with those 

in the highest ranked segments 
San Joaquin Valley Air Pollution Control District June 25, 2013 

D-9 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

• Negotiate a lease with a willing property owner in the highest ranked segment 

• Present site selection to the Governing Board for approval, and include the 

opportunity for public comments. 

3.2 Traffic Count Data 

Traffic count data determined which road segments would likely have the highest NO2

concentrations in the Bakersfield CBSA. Because truck traffic accounts for the highest 

NO2 emissions, the road segments were ranked by Fleet Equivalent Annual Average 

Truck Traffic (FE-AADT) counts. Areas that did not have recent truck traffic counts had 

to be estimated. 

While the percentage of statewide annual vehicle hours of delay caused by traffic 

congestion is far less in the San Joaquin Valley than in other areas of the state, the 

District included traffic congestion with the traffic count data as per the requirements 

outlined in the TAD. Caltrans District 6, which includes the Bakersfield CBSA, has less 

than 2% of the statewide annual vehicle hours of delay due to traffic congestion in the 

entire district. The highest ranking bottleneck locations where freeway speed dropped 

and remained below 60 mph are shown in Table 1 in below. Because so little traffic 

congestion occurs in the Bakersfield CBSA, congestion did not factor into site selection. 

3.2.1 Road Segment Ranking 

After the traffic data was examined, each road segment was ranked by FE-AADT from 

the highest traffic count to the lowest for the CBSA. The list was narrowed to the top 30 

road segments (see Appendix A) then reduced to the top 10 segments (see Table 1 

below). District staff surveyed the areas within each segment, and identified which 

locations could support a near-road monitoring station. 

 
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D-10 NO2 Near-Road Monitoring Station Siting Requirements 

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Table 1: Kern County Top Road Segments by Fleet Equivalent AADT4 

Route Postmile5 Description Ahead

AADT1 

AADT 

Rank AADTT AADTT Rank Congestion2 FE AADT6 

FE 

Rank

99 24.599 

BAKERSFIELD, 

CALIFORNIA 

AVE 

132,000 2 28,188 1 385,692 1 

99 22.604 BAKERSFIELD, 

MING AVE 133,000 1 27,720 2 1 382,480 2 

99 23.514 JCT. RTE. 58 

EAST 129,000 3 23,400 3 339,600 3 

99 21.082 BAKERSFIELD, 

WHITE LANE 114,500 4 17,500 5 272,000 4 

99 25.654 JCT. RTE. 58 W, 

JCT. RTE. 178 E 102,500 5 18,300 4 267,200 5 

99 26.776 BUCK OWENS 

BLVD 102,500 6 15,904 8 245,636 6 

99 19.541 PANAMA LANE 92,600 8 16,240 7 238,760 7 

5 15.8583 JCT. RTE. 99 

NORTH 72,000 11 17,410 6 228,690 8 

99 28.556 OIL JUNCTION 78,000 9 14,960 9 212,640 9 

99 27.866 OLIVE DRIVE 74,000 10 13,783 11 2 198,047 10 

1

 The Total AADT numbers shown apply to the freeway immediately ahead of the postmile. 

2

 Congestion data is in annual vehicle delay in thousand hours. Caltrans District 6 (which includes Kern County) 

 has less 2% of the statewide annual vehicle hours of delay. 

3

 Postmile 15.858 – Data for AADT was double counting the adjacent road segment. Caltrans has determined that 

the data is erroneous for this location and requested that the District use 2009 data. The annual traffic volume data 

shows that state freeway traffic decreased 0.2% in 2010 from 2009. 

4 The Annual Average Daily Traffic (AADT) is defined as the total volume for the year divided by 365 days. Very few 

 locations in California are actually counted continuously. Traffic Counting is generally performed by electronic 

 counting instruments that are moved from location to location throughout the state in a program of continuous 

 traffic count sampling. The resulting counts are adjusted to an estimate of annual average daily traffic by 

 compensating for seasonal influence, weekly variation and other variables which may be present. All traffic volume 

 figures that are listed include traffic in both directions. 

5 Postmile – Each breakpoint is identified by the postmile value corresponding to that point on the freeway. The 

 postmile values increase from the beginning of a route within a county to the next county line. The postmile values 

 start over again at each county line. Postmile values usually increase from South to North or West to East 

 depending upon the general direction the route follows within the state. 

6

 The equation FE AADT = (Ahead AADT-AADTT)+(AADTT*10) is defined in the TAD: 

 http://www.epa.gov/ttnamti1/files/nearroad/NearRoadTAD.pdf. 

3.2.2 The top 10 road segments 

With the exception of the road segment located on Interstate 5 from the Interstate 

5/Freeway 166 interchange to the Interstate 5/Freeway 99 interchange, the rest of the 

top 10 road segments are located along Freeway 99 through Bakersfield. The red lines 

in Figures 5a and 5b below demark the general location of the top 10 road segments. 

Gaps between the red lines along Freeway 99 depict locations of road segments that 

were ranked outside of the top ten and were not considered during the site selection 

process. This section contains descriptions of the 10 road segments and images of the 

segments are provided in Appendix B below. 

 
San Joaquin Valley Air Pollution Control District June 25, 2013 

D-11 NO2 Near-Road Monitoring Station Siting Requirements 

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Figures 5a and 5b: General location of the top 10 road segments in the 

Bakersfield CBSA. 

As shown in the TAD Matrix in Appendix A, road segment evaluations were based on 

many categories of criteria, however some of the categories were more critical to the 

decision-making process than others. In addition to meteorological considerations, the 

most important criteria included road design, road structures, and available space for an 

air monitoring site. Below are descriptions of the top 10 road segments and the reasons 

why they were acceptable or unacceptable for site consideration. 

3.2.2.1 Segment 1: Bakersfield, California Ave 

Segment 1 is located along Freeway 99 from California Avenue northward to Rosedale 

Freeway (JCT RTE 58). The southern and northern ends of segment are above grade 

and not acceptable for near-road monitor siting while the middle portion of segment is at 

grade with obstructions and space limitation issues along the segment. Trees align 

much of the segment and obstruct the air flow, and the above grade portion of the 
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segment consists of a bridge over a railroad yard and a river. The issues with this 

segment made it unacceptable for siting a near-road monitor. 

3.2.2.2 Segment 2: Bakersfield, Ming Ave 

Segment 2 is located along Freeway 99 from Ming Avenue northward to Highway 58 

(JCT RTE 58). The entire segment is below grade and characterized by upward slopes 

on both sides of the Freeway. Additionally, sound walls line the top of the slopes, and 

the interchange area is covered with mixed vegetation and trees. These characteristics 

of this segment made it unacceptable for siting a near-road monitor. 

3.2.2.3 Segment 3: JCT RTE 58 East 

Segment 3 is located along Freeway 99 from Highway 58 (JCT RTE 58) northward to 

California Avenue. The entire segment is below grade and both sides of the Freeway 

characterized by upward slopes with trees and ground vegetation on them. Additionally, 

sound walls line the top of the slopes on the west side of the freeway. These 

characteristics of this segment made it unacceptable for siting a near-road monitor. 

3.2.2.4 Segment 4: Bakersfield, White Lane 

Segment 4 is located along Freeway 99 from White Lane northward to Ming Avenue. 

The southern end of segment is at grade with sound wall limiting space on the east side 

of the freeway. The remainder of segment is below grade characterized by upward 

slopes on both sides of the freeway. Trees align most of the segment causing space 

limitation and air flow obstruction issues. These characteristics of this segment made it 

unacceptable for siting a near-road monitor. 

3.2.2.5 Segment 5: Buck Owens Blvd 

Segment 5 is located along Freeway 99 from Rosedale Freeway northward to Airport 

Drive. The central and southern sections of segment are above grade and serve as an 

overpass so there are no areas to consider along this stretch of the segment. The 

northern end of the segment is at grade but parcels that appear acceptable are too 

close to the slope of the above grade portion of the segment. Additionally, trees and 

bushes present space limitations and air flow obstructions along the remainder of the at 

grade portion of the segment. The issues with this segment made it unacceptable for 

siting a near-road monitor. 

3.2.2.6 Segment 6: JCT RTE 204 / Airport Drive 

Segment 6 is located along Freeway 99 from Airport Drive northward to Route 204. The 

southern tip of the segment is slightly above grade due to a small downward slope from 

the Freeway shoulder to the adjacent frontage road on the east side of the Freeway. 

The segment then levels to at grade until upward sloping of an overpass at the northern 

end of the segment creates a below grade area. Trees, bushes, and shrubs align much 

of the segment causing space limitations and air flow obstruction. The characteristics of 

this segment made it unacceptable for siting a near-road monitor. 
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D-13 NO2 Near-Road Monitoring Station Siting Requirements 

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3.2.2.7 Segment 7: Panama Lane 

Segment 7 is located along Freeway 99 from Panama Lane northward to White Lane. 

Figure 6 shows concentric circles depicting 100, 400, and 1,000 meters radii around the 

parcels in the segment. The 100 meter circle is the maximum extent of a microscale 

site. These concentric circles show the land uses around the parcels. Any of the 

parcels adjacent to these would have similar characteristics. 

The southern end and the center section of the segment are at grade and the northern 

end of the segment is above grade. With the exception of southern and northern tips of 

the segment, a sound wall and trees align the east side of the segment and pose space 

limitations. On the west side of the segment space intermittent trees along the segment 

and a sound wall aligning the southern tip of the segment prior to the off-ramp are the 

only space limitations. The District identified several parcels adequate for building a 

monitoring station however they were on the wrong side of the freeway with regard to 

the prevailing wind direction (see sample site in Figure 6). The space limitations and 

the prevailing wind issue make the segment unacceptable for siting a near-road 

monitor. 

 
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D-14 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

Figure 6: A sample site in Segment 7 that was not pursued because it was on the 

windward side of the freeway. 

The image in Figure 6 shows the other area that the District investigated in some detail. This area is on the west side 

of the freeway. The meteorological analysis ruled this site out because of the westerly winds. Starting from the 

north, the east side of the freeway is elevated and gradually comes down to the ground level where a sound wall 

starts. The sound wall continues all the way to the shopping center. The shopping center is too close to the freeway 

on-ramp to have a site placed there and they have planted trees along their fence line. Nearly the entire section of the 

west side of the freeway has space for an air monitoring station, initial contact with these landowners was made and 

the meteorological analysis removed them from consideration.

3.2.2.8 Segment 8: JCT. RTE. 99 North 

Segment 8 is located along Interstate 5 from the Interstate 5 – Freeway 99 JCT 

northwestward to Maricopa Freeway 166. The road is above grade on the interchange 

then descends to at-grade for remainder of segment to Maricopa Freeway 166. There 

are no roadside structures or space limitations along the segment. However, the 

surrounding land use is agricultural farming so property and not in an urban area. The 

District removed this segment from consideration because of the lack of population in 

the area. Given the relatively low population exposure in this rural segment, this 
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segment may not be representative of near-road exposure levels that occur in more 

urban areas with higher populations in the Bakersfield CBSA. 

3.2.2.9 Segment 9: Oil Junction 

Segment 9 is located along Freeway 99 from Norris Road northward to JCT Freeway 

65. The southern end of segment is above grade then descends to at grade for 

remainder of segment. While there are some space limitations along the segment, the 

District identified a few parcels in the central portion of the segment that are acceptable 

for near-road monitor placement. 

3.2.2.10 Segment 10: Olive Drive 

Segment 10 is located along Freeway 99 from Olive Drive northward to Norris Rd. The 

segment is at grade with intermittent trees and bushes aligning the segment. Space 

limitations are minimal however the frontage road adjacent to the freeway and the 

parcels and businesses located on the frontage road present accessibility issues which 

make the segment unacceptable for siting a near-road monitor. 

3.3 Meteorological Considerations 

As shown in the wind roses below, local winds in Bakersfield and along Interstate 5 

blow primarily from the northwest to the southeast. The Freeway 99 corridor runs 

through the city of Bakersfield in a north-south orientation. Interstate 5 runs from 

northwest to southeast along the west side of the Valley to the Freeway 99 interchange 

located south of Bakersfield. Given that the prevailing winds have a westerly 

component to them, the District determined that locations on the east side of Freeway 

99 and Interstate 5 were the most appropriate for near-road monitor placement and 

focused our efforts only on the east side of the freeway once the District made this 

determination. Air pollution from the freeway and the interstate would generally blow 

away from any monitor located on the west side of the freeway and interstate. 

Figures 7a through 7c: Wind Roses 

 7a. Bakersfield-Golden State Hwy 7b. Bakersfield-California Avenue 

 

Source: District EMC Data Program Source: District EMC Data Program 
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D-16 NO2 Near-Road Monitoring Station Siting Requirements 

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7c. Mettler Station AU491 

Source: University of Utah Meso West 

http://mesowest.utah.edu/cgi-bin/droman/download_ndb.cgi?stn=KSLC

3.4 Terrain through Bakersfield CBSA 

The terrain through Bakersfield CBSA is generally flat couple of bluffs caused by rivers. 

The Freeway 99 is generally at grade at the northern and southern limits of the city of 

Bakersfield and either elevated or below grade in the urban area of city. The Interstate 

5 segment is flat with farm fields on either side. There are sloughs and other low areas 

along this part of Interstate 5. Figure 8a shows a satellite image of the area under 

consideration in the city of Bakersfield and Figure 8b shows a satellite image of the 

terrain of the Interstate 5 segment. 

 
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and Selection Process for Bakersfield Core Based Statistical Area 

Figure 8a: Map of the Bakersfield Metropolitan Area

Figure 8b: Map of the Interstate 5 – Freeway 99 JCT Area 

3.5 Spatial scales and population exposure 

As stated above, NO2 near-road sites are intended to be microscale sites. This means 

that these sites measure representative concentrations within 100 meters. 

Representative concentrations measured over areas greater than this do not fit the 

definition of a microscale site. The TAD states that the highest concentrations can be 

found within 20 meters of the freeway, so the District focused efforts on locations that 

can handle an air monitoring site within 20 meters. Additionally, the required range for 
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D-18 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

the station’s probe height is 2 to 7 meters in order to capture the highest NO2

concentrations. While the preferred probe height is 2 meters, it will not be possible due 

to the structure and orientation of the monitoring station so, the District will place the 

probe as close to the 2 meter height as possible. 

As referenced above, population exposure as one of the criteria that should be 

considered during the site selection if you have multiple acceptable sites in the same 

road segment. For the Bakersfield CBSA there are only two segments that have 

potential multiple acceptable sites, segments 7 and 9. Segment 7 sites were eliminated 

due to wind direction and only one landowner in segment 9 was willing to negotiate a 

lease with us. 

Segment 8 was removed from consideration because it was not in an urban area and 

there were no population sources nearby. The District believes that people that are 

living, working, or commuting daily within and adjacent to the Bakersfield metropolitan 

area will have a more significant exposure than those using the segment of Interstate 5. 

Maps showing the locations that the District investigated in some detail are shown in 

Section 3 and Section 4. The maximum 100 meter radius of a microscale site is shown 

for reference. The 400 and 1,000 meter radii are shown for informational purposes. 

3.6 Correspondence with property owners 

The District found 19 acceptable parcels along Freeway 99 so letters of interest were 

sent to each of the property owners. Nine responses were received, however only 

seven of the property owners expressed interest. The District then began making direct 

contact with the seven interested land owners. Upon meeting with the representative of 

a landowner in Segment 7, the District discovered that the wind direction would be a 

problem and that lead to the elimination of all locations on the west side of the freeway. 

This issue left only three potential locations in Segment 9 from which to choose. One of 

the three potential sites would need extensive changes made to the property in order to 

accommodate an air monitoring station so that site was deemed infeasible. Of the two 

remaining potential sites, one of the landowners stopped talks with the District after 

reading the draft lease, but the other was willing to negotiate a lease so the process 

was able to move forward. 

4.0 Final Site Selection 

After everything was considered, the road segment with the 9th highest FE-AADT 

located at 2809 Unicorn Road was selected. The selected site meets the siting criteria 

listed in the CFR, and is also acceptable for accommodating placement of a PM2.5 and 

other air pollution analyzers in the future. 

Figure 9 is a map of the final site selection located on Unicorn Road in Segment 9, 

and. The concentric circles depict 100, 400, and 1,000 meters radii around the parcels 

in the segment. The 100 meter circle is the maximum extent of a microscale site. These 
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D-19 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

concentric circles show the land uses around the parcels. Any of the parcels adjacent 

to these would have similar characteristics. 

Figure 9: Final Section—2809 Unicorn Road 

The image in Figure 9 shows the location the District chose to locate the NO2 near-road site in Bakersfield CBSA. It 

is in segment 9 and the landowner is willing to work with the District. It is on the west side of the freeway and is in a 

light commercial area. There is a subdivision nearby on the east side of the freeway. 

Figure 10 below shows a roadside view of the selected site for the NO2 near-road air 

monitoring station. The site will be as close to the freeway as practicable. The vacant 

lot to the right and the adjacent parking lot with the building are on the same parcel. 

 
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D-20 NO2 Near-Road Monitoring Station Siting Requirements 

and Selection Process for Bakersfield Core Based Statistical Area 

Figure 10: Selected site located at 2809 Unicorn Road in Segment 9 

 
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D-21 NO2 Near-Road Monitoring Station Siting Requirements 

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APPENDICES 

 
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Appendix A —Traffic Data Tables 

Below is the list of the top 30 segments in the Bakersfield CBSA based on Caltrans 

data. 

Table 1: Kern County Top Road Segments by Fleet Equivalent AADT5

Route Postmile6 Description Ahead

AADT2 

AADT 

Rank AADTT1 AADTT Rank Congestion3 FE AADT7 

FE 

Rank

99 24.599 

BAKERSFIELD, 

CALIFORNIA 

AVE 

132,000 2 28,188 1 385,692 1 

99 22.604 BAKERSFIELD, 

MING AVE 133,000 1 27,720 2 1 382,480 2 

99 23.514 JCT. RTE. 58 

EAST 129,000 3 23,400 3 339,600 3 

99 21.082 BAKERSFIELD, 

WHITE LANE 114,500 4 17,500 5 272,000 4 

99 25.654 JCT. RTE. 58 W, 

JCT. RTE. 178 E 102,500 5 18,300 4 267,200 5 

99 26.776 BUCK OWENS 

BLVD 102,500 6 15,904 8 245,636 6 

99 19.541 PANAMA LANE 92,600 8 16,240 7 238,760 7 

5 15.858^ JCT. RTE. 99 

NORTH 72,000 11 17,410 6 228,690 8 

99 28.556 OIL JUNCTION 78,000 9 14,960 9 212,640 9 

99 27.866 OLIVE DRIVE 74,000 10 13,783 11 2 198,047 10 

58 53.519 SOUTH 

CHESTER AVE 72,000 12 13,770 12 195,930 11 

58 54.419 SOUTH UNION 

AVE 71,000 13 13,860 10 195,740 12 

99 27.046 

JCT RTE 

204/AIRPORT 

DRIVE 

102,500 7 10,294 21 195,146 13 

58 55.404 COTTONWOOD 

RD 70,000 14 13,084 13 187,756 14 

5 0.000 

LOS 

ANGELES/KERN 

CO LINE 

70,000 15 13,020 14 187,180 15 

58 53.387 H ST 70,000 16 11,750 15 175,750 16 

58 52.360 BAKERSFIELD, 

S. JCT RTE 99 68,000 20 11,487 16 171,383 17 

5 5.020 

FORT 

TEJON/DIGIER 

RD 

69,000 17 11,250 17 170,250 18 

5 13.523 WHEELER 

RIDGE RD 69,000 18 11,000 18 168,000 19 

5 1.612 LEBEC RD 69,000 19 10,890 20 167,010 20 

178 2.009 BAKERSFIELD, 

JCT. RTE. 204 67,000 21 10,962 19 165,658 21 

99 17.500 JCT. RTE. 119 

WEST 66,500 22 10,500 * 161,000 22 

 
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D-23 NO2 Near-Road Monitoring Station Siting Requirements 

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Table 1: Kern County Top Road Segments by Fleet Equivalent AADT5 (continued)

178 0.360 BAKERSFIELD, 

OAK ST 62,000 24 10,002 22 152,018 23 

99 29.878 JCT. RTE. 65 61,000 25 9,723 23 148,507 24 

99 30.532 SEVENTH 

STANDARD RD 62,500 23 9,000 * 143,500 25 

58 56.410 MT. VERNON 

AVE 60,000 26 8,473 24 136,257 26 

178 3.402 BAKERSFIELD, 

BEALE AVE 56,000 28 7,280 25 121,520 27 

99 52.450 POND RD 53,000 29 6,891 26 115,019 28 

99 50.410 MC FARLAND, 

ELMO HWY 53,000 30 6,749 27 113,741 29 

99 36.523 

CAWELO, 

LERDO 

FREEWAY 

59,500 27 6,000 * 113,500 30 

178 0.000 JCT. RTES. 99/58 52,000 31 6,640 28 111,760 31 

1

 Road segments with no Truck AADT (AADTT) are given substitution with the following: 

 Route 99: 

• PM 17.500 using 2/3 of adjacent segment Panama’s value = value of 10,500 

• PM 30.532 using JCT. RTE. 65, the segment had similar AADTT and was estimated at 9,000 

• PM 36.523 using JCT. RTE. 65, the segment had a large estimated exit volume of 6,000 at Lerdo Hwy 

2

 The Total AADT numbers shown apply to the freeway immediately ahead of the postmile. 

3

 Congestion is in annual vehicle delay in thousand hours. Caltrans District 6 (which includes Kern County) 

 has less than 2% of the statewide annual vehicle hours of delay. 

4

 PM 15.858 - Data for AADT was double counting the adjacent road segment. Caltrans has determined that the data 

 is erroneous for this location and requested that the District use 2009 data. The annual traffic volume data shows 

 that state freeway traffic decreased 0.2% in 2010 from 2009. 

5 The Annual Average Daily Traffic (AADT) is defined as the total volume for the year divided by 365 days. Very few 

 locations in California are actually counted continuously. Traffic counting is generally performed by electronic 

 counting instruments that are moved from location to location throughout the State in a program of continuous 

 traffic count sampling. The resulting counts are adjusted to an estimate of annual average daily traffic by 

 compensating for seasonal influence, weekly variation and other variables which may be present. All traffic volume 

 figures listed include traffic in both directions. 

6 Postmile - Each breakpoint is identified by the postmile value corresponding to that point on the freeway. The 

 postmile values increase from the beginning of a route within a county to the next county line. The postmile values 

 start over again at each county line. Postmile values usually increase from South to North or West to East 

 depending upon the general direction the route follows within the state. 

7

 The equation FE AADT = (Ahead AADT-AADTT)+(AADTT*10) is defined in the TAD: 

 http://www.epa.gov/ttn/amtic/nearroad.html 

Data source: 

Caltrans - All Vehicle http://www.dot.ca.gov/hq/traffops/saferesr/trafdata/2010all/2010_Traffic_Volumes.pdf 

Caltrans - Truck Data http://www.dot.ca.gov/hq/traffops/saferesr/trafdata/truck2010final.pdf 

Caltrans - Congestion http://www.dot.ca.gov/hq/traffops/sysmgtpl/MPR/pdfs/MPR2009.pdf 

Data accuracy of Caltrans AADT for 100,000 vehicles is approximately ± 6%

 
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Appendix B—Site Details 

Below are the site details for the selected site and the site that was ruled out because of 

meteorology. 

Table 2: Site Details Matrix

Site/Segment Parameter Segment 7

Car Dealership 

Segment 9

2809 Unicorn Rd 

Road segment name Segment 7 Segment 7 

Road segment end points Panama Lane to White 

Lane 

Norris Rd to JCT 

Hwy 65 

Road type Freeway Freeway 

Interchanges None None 

Frontage roads None None 

Roadside design At grade At grade 

Terrain Flat Flat 

Current road construction None None 

Future road construction Not aware of any Not aware of any 

Roadside structures None None 

AADT 95,600 78,000 

HD counts 16,240 14,960 

FE-AADT 238,760 212,640 

Congestion information No congestion No congestion 

Infrastructure At the street At the Street 

Surrounding land use Light 

Commercial/Industrial Light Commercial 

Nearby sources Freeway Freeway 

Meteorology Unacceptable Acceptable 

Population exposure Only parcel in segment Only parcel in 

segment 

Available space – site 

footprint 1000 square feet 1000 square feet 

Safety features None Will need to be 

installed 

Property type Private Property Private Property 

Property owner Not Applicable 

Likelihood of access Easy access Easy access 

Other details/local 

knowledge 

Landowner willing to work 

with us 

Landowner willing to 

work with us 

 
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Appendix C—Maps of Segments 

Beginning on the following page, aerial maps show the top 10 segments, their end 

points in detail, and the surrounding land use of each segment. 

 
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Segment 1 

This segment is located along Freeway 99 from California Avenue northward to 

Rosedale Freeway (JCT RTE 58). 

 Source: Google Earth 

 
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D-27 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 2 

This segment is located along Freeway 99 from Ming Avenue northward to Highway 58 

(JCT RTE 58). 

 Source: Google Earth 

 
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D-28 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 3 

This segment is located along Freeway 99 from Highway 58 (JCT RTE 58) northward to 

California Avenue. 

 Source: Google Earth 

 
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D-29 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 4 

This segment 4 is located along Freeway 99 from White Lane northward to Ming 

Avenue. 

 Source: Google Earth 

 
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D-30 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 5 

This segment is located along Freeway 99 from Rosedale Freeway northward to Airport 

Drive. 

 Source: Google Earth 

 
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D-31 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 6 

This segment is located along Freeway 99 from Airport Drive northward to Route 204. 

 Source: Google Earth 

 
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Segment 7 

Segment 7 is located along Freeway 99 from Panama Lane northward to White Lane. 

 Source: Google Earth 

 
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Segment 8 

Segment 8 is located along Interstate 5 from the Interstate 5 – Freeway 99 JCT 

northwestward to Maricopa Freeway 166. 

 Source: Google Earth 

 
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Segment 9 

This segment is located along Freeway 99 from Norris Road northward to JCT Freeway 

65. 

 Source: Google Earth 

 
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D-35 NO2 Near-Road Monitoring Station Siting Requirements 

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Segment 10 

This segment is located along Freeway 99 from Olive Drive northward to Norris Rd. 

 Source: Google Earth