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Multi-Pollutant Emissions Benefits of Transportation Strategies-FHWA

4. Transportation System Management Strategies

Transportation system management (TSM)strategies focus on changing the operation of the transportation system, typically with a primary focus on improving traffic flow and reducing traveler delay. TSM programs can reduce emissions by changing vehicle speeds and reducing vehicle idling. Many of these strategies are under the umbrella of Intelligent Transportation Systems (ITS). In addition, some strategies focus directly on encouraging changes in driving behavior through educational information, incentives, or restrictions on driving speeds, operating patterns, and idling.

Examining the emissions impacts of these strategies typically involves estimating travel speeds without the improvement and with the improvement in order to develop emissions factors in each situation. These emissions factors are then applied to VMT traveling along the facility. In some cases, additional VMT may be induced due to the travel speed change, and the increase in VMT should be accounted for in "with improvement" scenario.

TSM strategies, and associated methodologies and results, are presented below.

16. Signal Synchronization and Roadway Intersection Improvements

Strategy Overview

Corridor-wide or regional traffic flow improvements are designed to increase average travel speeds, reduce vehicle delay and idling, and result in fewer vehicle accelerations and decelerations. Specific projects include traffic signal synchronization, regional congestion management systems, and intersection improvements. Many of these projects involve elements of Intelligent Transportation Systems (ITS).

Emissions Impacts

In general, traffic flow improvements that reduce congestion should reduce emissions of most pollutants by improving the flow of traffic and minimizing stop-and-go conditions and idling. However, traffic flow improvement projects that increase travel speeds may have different effects on different pollutants. Although VOC emissions generally decline with increasing speeds, CO and NOx emissions begin to increase at speeds above about 32-35 miles per hour. As a result, improvements that increase speeds beyond these levels may increase CO and NOx emissions. In MOBILE6.2, particulate matter from exhaust and break and tire wear, SOx, and NH3 do not vary measurably by speed, given limited information on these emissions-speed relationships. Consequently, if a traffic flow strategy is examined solely as a speed change, no impact will be determined in MOBILE; however, if reduction in idling is accounted for, the strategy will typically show a reduction in all pollutants.

Table 4-1. Signal Timing - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease/no change

decrease/no change

decrease/increase

decrease/increase

generally decreases but possiblity of an increase based on starting speeds

decrease/no change

decrease/no change


↓* = Generally decreases, but possibility of an increase, based on starting speeds and level of speed change; N = No change; not quantified in EPA guidance

Some additional considerations with traffic flow improvement projects include the potential for diverted traffic and induced travel demand. Many corridor-based improvements result in some traffic that previously traveled on other routes switching to the improved roadway in order to reduce trip time. The increase in VMT on the corridor from diverted traffic should not be used in calculating increased emissions, since this is not new VMT in the system, but rather a movement of VMT from one route to another. Induced travel, on the other hand, represents new travel as a result of the roadway improvements. New vehicle trips might occur if people switch modes (from transit or walking or bicycling to driving), reduce average auto occupancy (switch from ridesharing to driving alone), or decide to take new trips. Longer trips may occur if people switch from closer destinations to more remote destinations, such as switching from a neighborhood shopping center to a regional mall. In general, the impact of induced travel is assumed to be relatively small for most signalization and intersection improvement projects. However, large-scale intersection improvements may discourage walking and bicycling if non-motorized travel is not effectively integrated.

It should also be noted that the impacts of most traffic signalization and intersection projects on speeds is limited to several years.Over the long-run, travel speeds may return to previous levels, although the roadway may be serving a larger volume of traffic.

General Considerations

The level of emissions impact depends on:

For more information, see EPA TCM Information Document, "Traffic Flow Improvements," http://www.epa.gov/otaq/stateresources/policy/transp/tcms/traff_improv.pdf

Sample Projects

Sample 1: Signal Coordination Project, Congested Arterial

This example is based on a project in California in which an old traffic signal controller was replaced with a new controller with expanded capacity.38

Step 1: Estimate total VMT affected by speed changes.

= (Days of use per year) x (segment length) x (congested traffic volume)
= (240 days) x (5 mi) x (3,000 vehicles)
= 3.6 million annual vehicle miles

Step 2: Calculated emissions reductions for affected traffic.

= (Project VMT) x [(emissions factor without project) - (emissions factor with project)]

Step 3: Calculate total emissions change as a result of the project.

= (Project VMT) x [(emissions factor without project) - (emissions factor with project)]

Table 4-2. Total Emissions Reduced (tons/year) from Signal Coordination on Congested Arterial Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.00

0.00

4.61

0.59

0.87

0.00

0.00

2010

0.00

0.00

3.69

0.41

0.60

0.00

0.00

2020

0.00

0.00

2.98

0.17

0.37

0.00

0.00



Sample 2: Signal Coordination Project, Less Congested Roadway

This project is similar to Sample 1, but is along an arterial with much higher average speeds.39 Project details include:

Step 1: Estimated total VMT affected by speed changes.

= (Days of use per year) x (segment length) x (congested traffic volume)
= (240) x (8.07 mi) x (88,643 vehicles)
= 178,837,253 annual vehicle miles affected

Step 2: Calculate total emissions change as a result of the project.

= (Project VMT) x [(emissions factor without project) - (emissions factor with project)]

In this case, the sample project results in a reduction in VOCs but an increase in CO and NOX due to increased travel speeds, which occur at the point where emissions rates begin to increase. Other pollutants show zero change since MOBILE6.2 emission factors are not sensitive to speeds.


Table 4-3. Total Emissions Reduced (tons/year) from Signal Coordination on Less Congested Roadway Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.00

0.00

Increase
18.9

0.76

8.52

0.00

0.00

2010

0.00

0.00

Increase
14.0

0.57

5.86

0.00

0.00

2020

0.00

0.00

Increase
7.00

0.38

3.22

0.00

0.00

17. Incident Management/Traveler Information

Strategy Overview

Incident management projects include service patrols that assist or remove the disabled vehicles from blocking travel lanes, computer systems that control traffic flow through intersections when incidents occur; and monitoring devices that scan roads and freeways for incidents and, in turn, either send assistance to injured or debilitated vehicles or help reroute traffic around incidents. If incidents are quickly cleared away, then vehicles do not have to idle in traffic as long. Incident management projects also minimize drivers' need to seek alternate routes to avoid congestion due to incidents. Alternate routes can frequently be longer than the original route, and so incident management can also result in some reduction in VMT. Combining incident management with enhanced traveler information can help to reduce the amount of time that vehicles experience delay.

Emissions Impacts

In general, incident management/traveler information programs that reduce congestion should reduce emissions of most pollutants by improving the flow of traffic and minimizing stop-and-go conditions and idling. However, incident management/traveler information projects that increase travel speeds may have different effects on different pollutants. Although VOC emissions generally decline with increasing speeds, CO and NOx emissions begin to increase at speeds above about 32-35 miles per hour. As a result, programs that increase speeds beyond these levels may increase CO and NOx emissions. In MOBILE6.2, particulate matter from exhaust and break and tire wear, SOx, and NH3 do not vary measurably by speed, given limited information on these emissions-speed relationships. Consequently, if a incident management/traveler information project is examined solely as a speed change, no impact will be determined in MOBILE; however, if reduction in idling is accounted for, the strategy will typically show a reduction in all pollutants.
General impacts of incident management are shown in the table below.

Table 4-4. Incident Management - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

decrease/no change

decrease/no change

decrease/increase

decrease/increase

generally decreases but possibility of an increase

decrease/no change

decrease/no change


↓* = Generally decreases, but possibility of an increase, based on starting speeds and level of speed change; N = No change; not quantified in EPA guidance

General Considerations

The level of emissions impact depends on:

Sample Project

Incident Management

This strategy provides an example of the emissions impacts from an incident management strategy from Arizona's I-20 Mile Marker 130, from July 1, 1999 to June 30, 2000.40 Calculations use calibrations based

on Actual Incident Scenarios simulated with CORSIM. The incident duration prior to project assumes the same percentage reduction in delay achieved by this system and involves the following factors:

Step 1: Estimate the average incident duration without and with the project.

= (Based on after-project duration divided by CHART after/before ration for vehicle hours)
= (43 min/67.5 million vehicle hours after/before)
= (67.5-43.6)/67.5 = 0.35
= 43 min / (1-0.35)/(60 min/hr)
= 1.1 hr

Average incident duration with project
= (43 min/(60 min/hr)
= 0.71 hr

Step 2: Calculate the average incident delay without and with project implementation.

= Incident delay without project
= e-10.19 x (traffic volume)2.8 x (avg. number of blocked lanes during incidents/Total number of lanes in project corridor)1.4 x Incident duration prior to project)1.78
= e-10.19 x (1700 vehicles/hr)2.8 x (1.11 lanes/3 lanes)1.4 x (1.1 hr)1.78 = 12,300 veh-hrs = Incident delay with project
= e-10.19 x (traffic volume)2.8 x (avg. number of blocked lanes during incidents/total number of lanes in project corridor)1.4 x (incident duration with project)1.78
= e-10.19 x (1700 vehicles/hr)2.8 x (1.11 lanes/3 lanes)1.4 x (1.1 hr) 1.78 = 12,300 veh-hrs
= e-10.19 x (1700 vehicles/hr)2.8 x (1.11 lanes/3 lanes)1.4 x (0.71 hr) 1.78 = 5,630 veh-hrs

Step 3: Calculate the change in delay per incident.

= (Incident delay without project) - (incident delay with project)
= (12,300) - (5,600) = 6,700 veh-hrs

Step 4: Calculate emission reductions per incident.

= (Change in delay) x (idle emissions factor)

Step 5: Calculate annual emission reductions.

= (Emissions reduced per incident) x (number of incidents per year)

The following table shows the annual emissions impacts resulting from the implementation of the example strategy:

Table 4-5. Total Emissions Reduced (tons/year) from Incident Management Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0

0

2.07

0.12

0.62

0

0

2010

0

0

1.62

0.08

0.41

0

0

2020

0

0

1.18

0.04

0.21

0

0


18. Speed Control

Strategy Overview

Speed reduction programs are usually implemented by local or state transportation or law enforcement agencies, primarily in order to improve safety.Speed controls can also reduce emissions and fuel consumption since emissions of certain pollutants are highest at travel speeds above 55 miles per hour.

Emissions Impacts

Programs that reduce travel speeds will not have proportionally the same effect on different pollutants since emissions-speed curves differ for each pollutant. In general, emissions tend to be lowest at speeds of 20-40 mph. In MOBILE6, particulate matter from exhaust and break and tire wear does not vary by speed.
General impacts of speed control are shown below.

Table 4-6. Speed Control - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

no change

no change

decrease/increase

decrease/increase

decrease/increase

no change

no change

N = No change; not quantified in EPA guidance

General Considerations

The level of emissions impact depends on:

Sample Project

Increased Adherence to the 60 MPH Speed Limit

This Transportation Control Measure would increase adherence to the speed limit on freeways, and lower average freeway speeds by 5 mph. This would be done through education of area motorists and increased enforcement. Data shows that over a 24-hour period, approximately 85 percent of autos using the freeway corridor being analyzed travel at speeds of 68 mph or less and 15 percent are over 68 mph. This is equivalent to an average speed of 62 mph. The measure would lower the 85th percentile to 63 mph, and the average speed to 57 mph. The freeway VMT for the 2.5 mile, 2-lane corridor being analyzed is 105,600 over a 24-hour period. There is no reduction in vehicle trips or vehicle miles of travel due to this measure41.The inputs for emissions impact calculations of the program include:

Step 1: Estimate the emission reduction.

= [(Base speed factor) x (freeway VMT)] - [(reduced speed factor) x (freeway VMT)]

The following table shows the annual emissions impacts resulting from the implementation of the example strategy:


Table 4-7. Total Emissions Reduced (tons/year) from Speed Control Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0.00

0.00

25.6

9.43

Increase 0.76

0.00

0.00

2010

0.00

0.00

19.5

6.33

Increase 0.47

0.00

0.00

2020

0.00

0.00

14.3

1.74

Increase 0.21

0.00

0.00

19. Shifting/Separating Freight Movements

Strategy Overview

Cities can regulate the movement of trucks within some areas of the region at certain times, changing the travel speeds for both trucks and other traffic and improving traffic flow. Historically, these programs have involved restricting trucks on local streets in certain areas of the central business district during peak hours, designating specific loading zones, delivery schedules, and truck routes, as well as multiple business delivery consolidation. Downtown areas or major business activity centers with alternate freeway and arterial routes available are often the best candidates for this type strategy. Some strategies are also voluntary, and are designed to create incentives for trucks to use roadways during off-peak time periods. Development of "truck only" lanes on highways is also a strategy to separate freight movement, and is often implemented primarily for traffic safety reasons.

Emissions Impacts

Measures to shift and/or separate freight movements generally should result in reduction in all pollutants, as shown in the following table. However, it is possible that increases in speeds by trucks could lead to increases in CO and NOx. There is also a small potential for induced traffic by light-duty vehicles associated with shifting truck traffic off heavily traveled commuter roads.

Table 4-8. Freight Movement Strategy - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

no change

no change

decrease/increase

decrease/increase

decrease with possible increase

no change

no change


↓* = Generally decreases, but possibility of an increase, based on starting speeds and level of speed change; N = No change; not quantified in EPA guidance

General Considerations

The level of emissions impact depends on:


Sample Project

Shifting Truck Trips to Off-Peak Periods

This example is based on the PierPASS program in Southern California. To help residents along freeway corridors, PierPASS instituted the OffPeak program to push truck trips into the evening and weekend hours to reduce the impact of big rigs on both truck and automobile congestion and idling. Containers entering or exiting marine terminals in the Ports of Los Angeles and Long Beach by road during peak daytime hours are charged a Traffic Mitigation Fee of $40 per TEU (20-foot equivalent unit), or $80 for all containers larger than 20 feet. The Traffic Mitigation Fee is not charged if the same container enters or exits the terminals outside of peak hours. The inputs for emissions impact calculations of this sample include:

Step 1: Calculate freight VMT affected by program.

= (Daily freight trips) x (road segment length)
= (2,000) x (70 miles)
= 140,000 freight miles

Step 2: Calculate emissions reduction.

= (Freight VMT) x [(freight emissions factor without project) - (freight emissions factor with project)]
= (140,000) x [(emissions factor without project) - (emissions factor with project)]

Note: the calculation demonstrates a very simplified procedure. This analysis could also account for the reduction in truck idle time while waiting to enter the port and changes in travel speeds for automobiles along the affected roadways.

Table 4-9. Total Emissions Reduced (tons/year) from Freight Movement Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

0

0

1.04

0.75

0.12

0

0

2010

0

0

0.63

0.22

0.09

0

0

2020

0

0

0.15

0.03

0.06

0

0

20. Vehicle Idling Restrictions/Programs

Strategy Overview

This emission reduction strategy attempts to reduce the amount of time that vehicles spend in idle mode as part of their overall operation. Examples of idling restrictions include controls on the construction and operation of drive-through facilities, such as banks, fast food restaurants, and pharmacies, and controls on extended idling during layover time, particularly of diesel engines used by transit vehicles and delivery trucks. Anti-idling restrictions on trucks and buses (as well as passenger cars) can be mandatory, voluntary, or incentive-based.

Emissions Impacts

Idling restrictions and programs can reduce emissions of all pollutants.

Table 4-10. Anti-Idling Strategy - Overall Impact on Emissions


PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

down arrow

down arrow

down arrow

down arrow

down arrow

down arrow

down arrow

General Considerations

Factors affecting level of emissions include:

For information on this strategy, see EPA TCM Information Document, "Extended Vehicle Idling," http://www.epa.gov/otaq/stateresources/policy/transp/tcms/extended_idling.pdf.

Sample Project

Closing 3 minute drive-thrus

Dallas County assessed the emission benefits of a light duty vehicle idling restriction policy. The proposed project would prohibit drive thru services during each day in which ozone levels exceed healthy levels. The policy would apply to fast food, restaurants, banks, pharmacies and dry cleaners42.Emissions calculations are based on the following factors:

Note that the increase in start exhaust emissions resulting from additional vehicles parking is included in the calculation.

Step 1: Calculate daily hours of idling reduced.

= (Number of vehicles using facilities) x (vehicles which park) x (average time spent idling)
= (100,000) x (1) x (.05)
= 5,000

Step 2: Calculate ozone season hours of idling reduced.

= (Daily hours of idling reduced) x (number of ozone days)
= (5,000) x (17)
= 85,000

Step 3: Calculate idling emissions reduction.

= (Ozone season hours of idling reduced) x (idling emission factor)
= (85,000) x (idling emissions factor)

Step 4: Calculate trip starts emissions increase.

= (Vehicles which park) x (trip starts emissions factor)
= (1) x (trip start emissions factor)

Step 5: Total emissions reduced.

= (Idling emissions reduction) - (trip starts emissions increase)

Table 4-11. Total Emissions Reduced (tons/year) from Anti-Idling Example


Year

PM-2.5

PM-10

CO

NOx

VOCs

SOx

NH3

2006

<0.01

<0.01

0.77

0.03

0.04

<0.01

<0.01

2010

<0.01

<0.01

0.42

0.02

0.02

<0.01

<0.01

2020

<0.01

<0.01

0.36

0.01

0.01

<0.01

<0.01

38 Documented in "Methods to Find the Cost-Effectiveness of Funding Air Quality Projects," by the California Air Resources Board, 2005.

39 Based on strategy documented in "Methods to Find the Cost-Effectiveness of Funding Air Quality Projects," by the California Air Resources Board, 2005.

40 Documented in "A Guide for Estimating the Emissions Effects and Cost-Effectiveness of Projects Proposed for CMAQ Funding," by ICF International for the Birmingham Regional Planning Commission, 2002.

41 Documented in the Metropolitan Planning Technical Report, "Transportation Control Measures Analyzed for the Washington Region"s 15 Percent Rate of Progress Plan," 1995.

42 Documented in ";8-Hour Attainment: Control Strategies: On Road," by ENVIRON Corp. for North Central Texas Council of Governments, 2006.

Updated: 07/06/2011
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