POET-ML Framework

Figure 1 illustrates the analytical process used in POET-ML. 

Figure 1: POET-ML Framework

Step 1: Operational Assessment of Existing HOV Facility

The initial step in the model process is an assessment of the operational effectiveness of the existing HOV facility. This assessment considers both physical and operational characteristics including number of lanes, length, separation, eligibility, and demand, among others. 

In this step, the user can select a specific HOV facility from the FHWA Highway HOV Facility Inventory database that includes information on HOV policy details and physical characteristics. The user is then required to enter the number of HOV lanes and GP lanes in each direction during peak hour operations as well as the corresponding volumes in these lanes (records highlighted in red). Other information, such as public transportation vehicles (no. of buses per hour); percentage of motorcycles; percentage of taxi and percentage of low emission and/or energy efficient vehicles, is optional. Once valid values are entered for these items, the user can continue with the analysis. It is also possible to store a specific profile for future use by modifying the text for one or more of the input data field records.

Table 1 outlines the set of information to be populated either from the FHWA Highway HOV Facility Inventory database or by the user. The data was grouped into four major categories.  General information, physical characteristics, and HOV policies should be readily available to nearly any user familiar with the HOV system under consideration.  However, travel demand and operational performance could be more difficult to obtain.

Table 1: User Inputs

Data Category	Data Requirement	Data Sources	Requirement
General Information	State / Province	FHWA Highway HOV Facility Inventory	Required
	City / County	FHWA Highway HOV Facility Inventory	Required
	Urban Area	FHWA Highway HOV Facility Inventory	Required
	Road name	FHWA Highway HOV Facility Inventory	Required
	Segment (from/to)	FHWA Highway HOV Facility Inventory	Required
Physical Characteristics	Route Miles	FHWA Highway HOV Facility Inventory	Required
	No of HOV Lanes Per Direction	User Input	Required
	No of General Purpose Lanes Per Direction	User Input	Required
	Type	FHWA Highway HOV Facility Inventory	Optional
	Intermediate Access	FHWA Highway HOV Facility Inventory	Optional
	Separation	FHWA Highway HOV Facility Inventory	Optional
HOV Policies	Eligibility HOV	FHWA Highway HOV Facility Inventory	Required
	Eligibility Toll	FHWA Highway HOV Facility Inventory	Optional
	Eligibility Motorcycle	FHWA Highway HOV Facility Inventory	Optional
	Eligibility Taxi	FHWA Highway HOV Facility Inventory	Optional
	Eligibility Special Fuel	FHWA Highway HOV Facility Inventory	Optional
	Eligibility Others	FHWA Highway HOV Facility Inventory	Optional
	Hours of Operation	FHWA Highway HOV Facility Inventory	Optional
Travel Demand and Operational Performance	HOV Lane Volume (Peak Hour) in Peak Direction*	User Input	Required
	GP Lane Volume (Peak Hour) in Peak Direction*	User Input	Required
	Public transportation vehicles (no. of buses per hour)	User Input	Optional
	Percentage Motorcycles	User Input	Optional
	Percentage Taxi	User Input	Optional
	Percentage Low emission and/or energy efficient vehicles	User Input	Optional

* Volumes represent demand for the corridor by lane type.

 

Figure 2: Model Input Page

User input, to be input to the model using the interface shown in Figure 2, will supply the information necessary to assign the HOV facility to one of two categories based on the established performance thresholds, such as volume-to-capacity ratios or service flow rate (pc/h/ln). These categories describe the general performance of the facility in terms of utilization.  During step 2 of this process, the user will be presented with a set of policy adjustments based on the specific category to which the facility is assigned.  Table 2 outlines the two categories and corresponding performance thresholds by default.

Table 2: HOV Facility Performance Thresholds

Categories	Volume-to-Capacity Ratios	Service Flow Rate (pc/h/ln)
HOV facility that has excess capacity during both peak and off-peak periods;	Peak Hour V/C Ratio <0.75	Peak Hour Service Flow Rate < 1650 pc/h/ln
HOV facility that is congested during the peak period and has excess capacity during the off-peak period.	Peak Hour V/C Ratio >=0.75	Peak Hour Service Flow Rate >= 1650 pc/h/ln

 

It is important to note that the default threshold values of V/C ratio (0.75) and service flow rate (1650 pc/h/ln) were established based on aggregated national survey results, and they are consistent with the assumptions in FHWA’s Spreadsheet Model for Induced Travel Estimation - Managed Lanes (SMITE-ML). The default values of V/C ratio and service flow rate are stored in the POET-ML parameters page and remain interactive and transparent to the user. Users are allowed to adjust these values to reflect the unique characteristics of facilities in their region. To review and/or modify the default model parameters navigate to the Potential Impacts page and select “Adjust Parameters.”

The precision of the analysis will depend on the availability of data from the user, and the quality of the final model output depends entirely on the user’s ability to supply as much needed information as possible.

Step 2: Identification of the required and/or optional HOV policy changes

A set of applicable policy adjustments are introduced in step 2 of the model process, based on the assessment from step 1.  If it is determined that the HOV facility has excess capacity in both the peak and off-peak periods, the user will be shown a number of policy change options related to vehicle occupancy, vehicle eligibility, and pricing.  In order to fill unused HOV capacity, and avoid empty lane syndrome, the user could choose to lower the occupancy restrictions (e.g. from HOV3+ to HOV2+) or to allow additional free vehicles (e.g. public transportation vehicles, taxis, motorcycles, hybrid vehicles, etc.).  Additionally, the user could convert the lanes from HOV to high-occupancy toll (HOT) lanes, and sell excess capacity to users not permitted in the lanes but who would be willing to pay for the travel time savings these lanes provide.  These policy changes could also be bundled together in some combination that both achieves the utilization targets and meets the goals of the region.  Table 3 shows the options to be presented to the user.

The same set of policy change options applies for HOV facilities determined to be congested during peak periods.  However, the potential adjustments will be more restrictive, rather than less restrictive, as was the case for the excess-capacity scenario.  For example, one option to address congested HOV lanes is to increase the occupancy requirements (e.g. from HOV2+ to HOV3+).  Likewise, non-carpools that are currently eligible to use the HOV lanes could be prohibited (e.g. disallow motorcycles, transit vehicles, etc.).  Pricing of non-eligible vehicles can also be implemented on congested HOV lanes, but it must be bundled with some other policy shift.  Once demand in these lanes is brought down below capacity through more restrictive policies, any remaining capacity could be sold to ineligible vehicles (i.e. those not meeting the current occupancy/eligibility policy) that are willing to pay for access. In addition to policy change options related to vehicle occupancy, vehicle eligibility, and pricing, the user can also explore the impacts of adding an additional managed lane.  This option is only available for HOV facilities that are congested during peak period. This could either be an additional lane in each direction, or an additional reversible lane, depending on the facility. By adding additional capacity, it provides increased flexibility for HOV operators and eliminates the need for immediate occupancy policy changes.  Table 4 shows the options for the congested peak period condition.

If HOV demand is deemed to be on target during peak periods (i.e. neither underutilized nor congested), there are still opportunities for policy adjustment.  Future demand may eventually lead to congestion in lanes that are operating well today, and proactive steps could ensure efficient operation for years to come.  Pricing is always an option that provides flexibility for HOV operators to manage demand in these lanes in order to achieve more efficient use.  Occupancy and eligibility policy changes alone, offer only discrete solutions that may tip the utilization balance too far in one direction.

 

Table 3: Potential Policy Adjustments for Facilities with Excess Capacity Condition (Empty Lane Syndrome)

Operating Element	Direction of Change	Details	Policy Change Options	Value
Vehicle Occupancy (HOV)	Decrease	By relaxing the vehicle occupancy restrictions, more vehicles could gain access to HOV lanes, filling unused capacity in the currently underutilized lanes.	Vehicle Occupancy (HOV)	2+
Free Vehicle Eligibility	Less Restriction	By allowing vehicles that don't meet the existing vehicle eligibility policy (e.g. low emission and energy-efficient vehicles) to use the HOV lanes, more vehicles could gain access to these lanes, filling unused capacity.	Public transportation vehicles (no. of buses per hour)	50
			Motorcycles	1%
			Taxi	2%
			Low emission and/or energy efficient vehicles	4%
Pricing	Allow Paying Vehicles	For the existing HOV lanes which are underutilized, allowing vehicles that don't meet passenger occupancy or vehicle eligibility requirements to gain access to HOV lanes by paying a toll provides the opportunity to fill unused capacity and also provides transportation choice for those willing to pay. By pricing those previously ineligible vehicles, new revenue is generated that could, if authorized, be utilized for transportation improvements.	Paying vehicles	Allow

 

Table 4: Potential Policy Adjustments for Facilities with Congested Peak Period Conditions

Operating Element	Direction of Change	Details	Policy Change Options	Value
Vehicle Occupancy (HOV)	Increase	By increasing the vehicle occupancy requirement, some currently eligible HOVs are diverted from the lanes, providing additional capacity in currently overutilized HOV lanes.	Vehicle Occupancy (HOV)	2+
Free Vehicle Eligibility	More Restrictions	By disallowing some currently eligible vehicles, additional capacity is freed up in the overutilized HOV lanes.	Public transportation vehicles (no. of buses per hour)	0
			Motorcycles	0%
			Taxi	0%
			Low emission and/or energy efficient vehicles	0%
Pricing	Allow Paying Vehicles	Pricing needs to be bundled with a vehicle occupancy change, (free) vehicle eligibility change, and/or capacity change for the facility that is overutilized. By pricing those previously ineligible vehicles, new revenue is generated that, if authorized, could be utilized for transportation improvements.	Paying vehicles	Allow
Additional Capacity	Add a Managed Lane	Building additional capacity provides increased flexibility for HOV operators facing peak period congestion. Additional capacity eliminates the need for immediate policy changes.	Capacity	Disallow

Step 3: Evaluation of Potential Impacts

The third step in the process is to assess the impacts of the HOV lane policy change or combination of policy changes that were selected in step 2.  The tool will track four key measures of effectiveness: travel demand impacts, mobility impacts, environmental impacts, and financial feasibility.

Travel Demand Impacts

Both vehicle and person travel demand will be examined over daily and peak hour periods in the HOV/HOT and general-purpose (GP) lanes.  Travel will be broken down into carpools, transit, motorcycles, special fuel vehicles, taxis, and paying vehicles. At a minimum, the user will be required to supply information on peak hour vehicle trips for each vehicle type under the current HOV policies.  Relationships coded into the tool will be used to calculate peak hour person trips and daily vehicle and person trips.   

Travel demand impact calculations will depend heavily on which of the two conditions (excess capacity or congested) applies to the facility under evaluation. If pricing is selected as a policy change, the level of travel demand in priced lanes will be maintained at Level of Service C during the peak hour, by default, i.e., about 75% of absolute capacity.  Paying vehicle volumes in priced lanes during the peak hour are estimated to be equal to the spare vehicle capacity that would be available on the lanes at a Level of Service C.  The balance of the volume is occupied by non-paying vehicles.

A number of combinations exist between existing conditions and subsequent policy adjustments.  The algorithms in place to determine final volumes for both HOV/HOT lanes and general purpose (GP) lanes are different based on the combination under consideration.  Following are four potential scenarios, meant to outline the different calculation processes executed by POET-ML.  Each scenario description includes a table with example output data and a figure showing general travel conditions in the corridor.  Following these scenarios is a detailed description of the calculations for mobility and environmental impacts, along with financial feasibility.

Scenario 1: HOV & GP Lanes Both Under Capacity

Many corridors with HOV lanes are uncongested in peak periods. Under these conditions, no changes are required to bring HOV operating speeds back to acceptable levels.  However, the HOV operator may be interested in seeing the impact of implementing pricing, or of allowing additional vehicles into the HOV lanes through occupancy or eligibility changes.  Figure 3 illustrates the potential impact of allowing priced vehicles into the HOV lanes.  The colored arrows represent the flow conditions for each lane in the corridor.  Table 5 shows an example calculation for this scenario. 

Of the 1,100 peak hour HOV trips in the existing condition, 1,004 of them are carpools.  The rest are other eligible vehicles.  These other vehicles generally make up a small proportion of total HOV demand, and therefore changes to eligibility restrictions could have little direct impact on HOV and GP lane performance.

Initially, this uncongested corridor experiences LOS C conditions in the GP lanes and LOS A/B conditions in the HOV lane.  Allowing priced vehicles in the HOV lane will attract additional users because of the time savings relative to the GP lanes.  POET-ML pulls these users from two different places: the GP lanes and parallel facilities.  The percent split from these sources depends on the conditions in the GP lanes.  As the V/C ratio in the GP lanes rises, the contribution of vehicles from these lanes to the HOV/HOT lane also rises.  When GP conditions are near LOS A/B, a larger portion of vehicles are diverted from parallel facilities to the HOV/HOT lane.  The final volumes in the HOT lane under this condition are no higher than the maximum LOS C volume defined in the Tool.  Nor are they larger than ¼ the total corridor volume (¼ because the facility has 4 total lanes, with one HOV lane).  This is to ensure that HOT operating speeds do not fall below GP speeds, which is a possible, but unlikely scenario.  For these reasons, revenue is likely to be minimal under this condition.  Obviously, few motorists would be willing to pay a toll to use the HOT lane when only minimal time savings can be realized.

Indeed, Table 5 shows just 300 paying vehicles after the policy change, bringing the peak hour total in the HOV/HOT lane to 1,400.  Volumes decrease from a total of 4,500 on the GP lanes to 4,380.  With a per lane capacity of 2,200 vehicles per hour, the GP lanes have a similar V/C ratio to that of the HOV/HOT lane, which is the reason for the low demand from paying vehicles in that lane.

Figure 3: Scenario 1 Lane Condition Diagrams

 

Scenario 2: HOV Lane Under Capacity and GP Lanes Congested

Another common scenario involves congested GP lanes adjacent to an HOV facility that operates well below capacity.  Again, the operator is not required to make policy changes in order to maintain an acceptable LOS in the HOV lane, but there may be interest in achieving greater utilization in this lane.  Options for increasing HOV volumes include relaxing occupancy and eligibility restrictions in the lanes, as well as allowing previously ineligible vehicles (e.g. single-occupant vehicles) to pay a toll in order to use the lane.  These options would have different impacts on lane volume, however, and caution needs to be observed to avoid creating congested HOV conditions.  For example, lowering the occupancy restriction from 3+ to 2+, if applicable, could potentially allow too many vehicles into the HOV lane, degrading performance below acceptable levels. 

In this example, a congested corridor has an underutilized HOV lane. This condition is commonly referred to as “empty lane syndrome,” and is one key motivator for HOV policy change.  Allowing priced vehicles access to the HOV lane can lead to improvements in the GP lanes and better use of the HOV lane.  One likely outcome of this change can be seen in Figure 4.  Here, LOS improves from ‘E/F’ to ‘D’ on the GP lanes, while LOS degrades slightly on the HOV/HOT lane from ‘A/B’ to ’C’.  In POET-ML, most of the priced vehicles in the HOT lanes come from the GP lanes under these conditions, with a small contribution from parallel facilities.  As a result, total corridor throughput increases slightly under this scenario.  As noted previously, vehicle contribution from these two sources is determined based on a sliding scale with a 70/30 split between parallel facilities and GP lanes when the GP lanes operate at LOS A.  This split changes to 60/40 under LOS B, 50/50 under LOS C, 40/60 under LOS D, and 30/70 under LOS E/F conditions.  This distribution is included in the parameters page, and can be modified by the user.

HOT lane volumes are capped at the LOS C capacity, which is accomplished in practice through demand-responsive, variable tolling.  If pricing is not a viable alternative, an HOV operator could still achieve greater corridor throughput by increasing the types of eligible vehicles in the HOV lane.  Allowing hybrids or special fuel vehicles, taxis, or additional transit vehicles can provide a degree of relief to the GP lanes while increasing utilization of the HOV lane.  However, as discussed previously, relaxing eligibility restrictions may not impact many vehicles, and therefore conditions may not change much in the corridor.
Table 6 shows example output from this scenario.  Here, HOV volume is brought to capacity after pricing is allowed, and GP lane conditions improve with decreases of more than 100 vehicles per lane.  Again, total corridor throughput increases over the existing case.  Pricing allows for more efficient movement in these 4 lanes.

 

Figure 4: Scenario 2 Lane Condition Diagrams

 

Scenario 3: HOV Lane and GP Lanes Over Capacity (Increased Restrictions)

Some HOV facilities are congested during peak periods and require policy adjustment in order to maintain federally mandated performance standards.  Low cost strategies for decreasing HOV lane volume include increasing occupancy restrictions and implementing more exclusive eligibility criteria.  However, efforts to divert vehicles from the HOV lanes can lead to increased congestion on GP lanes.  And if HOV lane rules are made too restrictive, traffic could fall well below LOS C conditions, leading to empty lane syndrome.  For example, in many urban areas, the vast majority of HOVs have just 2 occupants, with only a small percentage of 3+ occupant vehicles.  If the HOV operator increases the occupancy restriction from 2+ to 3+, many of the vehicles in the lane will no longer be eligible, and will be diverted to the GP lanes or parallel facilities. 

POET-ML takes into account the overcapacity scenario described above.  Once it is determined that the HOV lane is congested in peak periods, the user is presented with a list of potential policy changes designed to achieve improved HOV operating conditions.  The greatest impact usually comes from increased occupancy restrictions.  Figure 5 shows an example of the impact of first increasing this restriction from 2+ to 3+, followed by allowing priced vehicles in the lane. 

The first selection shifts a large number of vehicles from the HOV lane to the GP lanes.  Of course, the number of vehicles diverted will vary by facility, according to the regionally-specific HOV mix (i.e. the relative number of HOV2, HOV3, HOV 4+, etc.).  This split is coded as a parameter in the Tool, and it can be updated by the user as desired.  If the user changes only the occupancy restriction, total corridor volume will remain constant, and GP lane conditions will likely become even more congested.  In addition, it is possible that the HOV lane may exhibit LOS A/B conditions, which is suboptimal utilization.  If the user follows this selection by allowing pricing in the HOV lane, however, vehicles return to the lane and fill the unused capacity.  POET-ML pulls most of the priced vehicles from the GP lanes, and a smaller portion from parallel facilities.  This split is also coded as a parameter in the Tool, and if the user desires to vary the source of priced vehicles, he or she has that flexibility.  Once both decisions are executed, conditions are likely to appear as they do on the right of Figure 5.

Table 7 shows the extent to which the GP lanes become more congested in this scenario.  Of course, the HOV lane is maintained at the LOS C capacity, and most of these vehicles are tolled.  HOV3+ vehicles, along with other eligible free vehicles, comprise the balance of the lane volume.  The HOV2 vehicles, which were pushed to the GP lanes in response to the occupancy policy change, are responsible for the increased GP lane congestion.

 

Figure 5: Scenario 3 Lane Condition Diagrams

Scenario 4: HOV Lane & GP Lanes Over Capacity (Additional Capacity)

Another option for addressing a corridor with congested HOV and GP lanes is to add HOV/HOT capacity.  In locations where available right of way affords such an investment, this option can provide a high degree of flexibility for HOV operators.  Additional HOV capacity allows greater opportunities for efficient corridor flow and can eliminate the need for occupancy and/or eligibility policy change.  In the scenario highlighted in Figure 5, the user has opted to add HOV capacity and implement tolling in these lanes.  In doing so, corridor conditions are improved for both the managed and GP lanes.  In addition, total corridor volume increased, which means the facility can serve more vehicles, more efficiently than before.  And all of this is possible while maintaining occupancy restrictions of 2+.  This last point is important, because raising occupancy restrictions can be controversial.  Those that have formed 2 person carpools to use the HOV lanes will likely object to any change in policy that forces them out of the lanes.  Additional capacity can help avoid this situation.

In the scenario highlighted in Figure 6, the user has chosen to address corridor congestion by maintaining the existing HOV policy, adding a lane of HOV/HOT capacity, and implementing pricing on both lanes.  POET-ML is equipped to respond to each of these decisions and to calculate the final conditions on the managed and GP lanes.  The additional HOV lane doubles the capacity for qualifying vehicles.  These vehicles are spread evenly over the two lanes, which likely eliminates peak period congestion.   Allowing priced vehicles fills unused capacity in these lanes while helping to improve conditions in the GP lanes.  Again, the majority of paying vehicles are taken from the GP lanes, with a smaller percentage diverted from parallel facilities.

The number of free vehicles in the HOV lanes remains the same both before and after the capacity addition, as shown in Table 8.  This allows for a 1,100 paying vehicles to enter the HOV/HOT lanes, bringing both lanes to their LOS C capacity.  Since many of those paying vehicles come from the GP lanes, total GP volume decreases from 6,700 to 5,930, resulting in improved LOS on these lanes as well.

 

Figure 6: Scenario 4 Lane Condition Diagrams

Additionally, POET-ML analyzes the peak hour person trips based on occupancy rate for different vehicle types. It also analyzes the total daily vehicle trips and total daily person trips based on Peak Hour vehicle/person trips and the daily to Peak Hour Conversion factor. Table 9 outlines those travel demand impacts and its corresponding calculation methodology. The table also includes values from the earlier example.

Table 9: Daily Conversion Formulas

Travel Demand Impacts	With Existing HOV Policy and With Selected Policy Changes
Total Peak Hour Person Trips	HOV Lane: Peak Hour (Carpools (Free) + Buses + Motorcycles + Taxi + Special Fuel + Paying Vehicles) Persons GP Lane: Peak Hour GP Lane Vehicle Trips * Carpool Occupancy Rate HOV Lane: =4,665 + 200 + 0 + 36 + 36 + 0 = 4,938 GP Lane: =11,250 * 1.1 = 12,375
Peak Hour Carpool Persons (Free)	Peak Hour Carpools (Free) Vehicles Trips * Carpool Occupancy Rate =2,121 * 2.2 = 4,665
Peak Hour Others (Transit)	Peak Hour Bus Vehicles Trips * Bus Occupancy Rate =10 * 20 = 200
Peak Hour Motorcycle	Peak Hour Motorcycle Trips * Average Auto Occupancy Rate =0 * 1.1 = 0
Peak Hour Taxi	Peak Hour Taxi Trips * Average Auto Occupancy Rate =17 * 2.1 = 36
Peak Hour Special Fuel	Peak Hour Special Fuel Vehicle Trips * Average Auto Occupancy Rate =33 * 1.1 = 36
Peak Hour Tolling	Peak Hour Tolling Trips * Average Auto Occupancy Rate =0
Daily
Total Daily Vehicle Trips	HOV Lane: Peak Hour (Carpools (Free) + Buses + Others + Paying Vehicles) GP Lane: Peak Hour GP Lane Vehicle Trips * Daily to Peak Hour Conversion Factor HOV Lane: =25,452 + 120 + 600 + 0 = 26,172 GP Lane: =11,250 * 12 = 135,000
Daily Carpools (Free) in HOV Lane*	Peak Hour Carpools (Free) * Daily to Peak Hour Conversion Factor =2,121 * 12 = 25,452
Daily Buses in HOV Lane*	Peak Hour Buses * Daily to Peak Hour Conversion Factor =10 * 12 = 120
Daily Others in HOV Lane*	Peak Hour (Motorcycles + Taxi + Special Fuel Vehicles) * Daily to Peak Hour Conversion Factor =(0 + 17 + 33) * 12 = 600
Daily Paying Vehicles in HOV Lane*	Peak Hour Paying Vehicles (Free) * Daily to Peak Hour Conversion Factor =0
Total Daily Person Trips	HOV Lane: Daily (Carpools (Free) + Buses + Others + Paying Vehicles) GP Lane: Peak Hour GP Lane Vehicle Trips * Daily to Peak Hour Conversion Factor HOV Lane: =55,980 + 2,400 + 864 + 0 = 59,244 GP Lane: =12,375 * 12 = 148,500
Daily Carpool Persons (Free) in HOV Lane*	Daily Carpools Persons (Free) * Daily to Peak Hour Conversion Factor =4,665 * 12 = 55,980
Daily Bus Passengers in HOV Lane*	Daily Buses Passengers * Daily to Peak Hour Conversion Factor =200 * 12 = 2,400
Daily Other Persons in HOV Lane*	Peak Hour (Motorcycles Persons + Taxi Persons + Special Fuel Persons) * Daily to Peak Hour Conversion Factor =(0 + 36 + 36) * 12 = 864
Daily Paying Persons in HOV Lane*	Peak Hour Paying Persons (Free) * Daily to Peak Hour Conversion Factor =0

*Only applies to HOV Lane.

Mobility Impacts

The travel demand impacts will then be used to determine the facility operating conditions, including the volume-to-capacity ratio, operating speed, level of service, facility travel time, total vehicle travel delay, etc. Again, these impacts will be examined over daily and peak hour periods for both the HOV and GP lanes.

To calculate each of the mobility impacts, a number of assumptions are embedded into the calculations of these impacts. Examples of values the user may wish to update include Hourly Freeway Capacity per Lane (vph), Free Flow Speed (mph), the values for “alpha” and “beta” used in the Bureau of Public Roads equation for computing congested Peak Hour and Daily Travel Speeds, V/C thresholds for Level of Service, etc. All these assumptions are stored in the POET-ML Parameters Page. The user will have explicit access to change these assumptions if desired to better fit the characteristics of specific facilities and areas.

The calculations for mobility impacts are built with flexibility in mind, allowing the user to customize the assumptions to a specific region, if the data supports it, and if there is a desire for greater precision in the results. If not, the user can work with the set of assumptions that emerged out of the model calibration effort, which will be based on nationwide averages.

Table 10 outlines the information to be included for these mobility impacts and the detailed calculation methodology of those mobility impacts. The table also fills in these formulas, under the existing conditions, with values from the example cited earlier.

Environmental Impacts

POET-ML will use the traffic volume estimates and mobility impact estimates to evaluate the environmental effects of the HOV facility under consideration. Two key environmental indicators will be examined, including air quality performance and carbon dioxide.

The quantity of gasoline conserved can directly relate to reduced vehicular emissions. Gasoline savings were based on numbers derived using Texas Transportation Institute assumptions of 0.68 gallons of fuel per hour of delay. The evaluation will consider changes in total vehicle delay as a result of the policy adjustment package selected by the user and estimate the fuel-based emissions based on gas savings and estimated vehicular emission rates per gallon. Due to the difficulty in determining advancement in emissions technology, the values used in POET-ML reflect modern day estimated emission rates, as illustrated in Table 11 .

For example, if the model results predict a reduction in total vehicle travel delay as a result of a conversion form HOV lanes to HOT lanes, POET-ML will model changes in air quality and carbon dioxide emissions based the above average rates. The user will be able to see the impact of any delay reduction in environmental terms.

Table 12 outlines the information to be included for the environmental impacts and the calculation methodology of these two performance measures. The table also fills in these formulas, under the existing conditions, with values from the example cited earlier.

Again, the user will have access to adjust all the estimated emission rates for CO (kg/gallon), NO_x (kg/gallon), VOC (kg/gallon) and Carbon Dioxide (kg/gallon) in the POET-ML Parameter page if desired.

Financial Feasibility

The final measure of effectiveness is financial feasibility. The set of policy adjustments includes pricing of existing HOV lanes, and if pricing is selected, it will trigger additional analysis in the model. Again, the user will have access to assumptions behind these calculations, including value of time estimates, weekend/weekday revenue ratios, and per-transaction tolling operation costs. The model incorporates national averages for these inputs and uses the results from the mobility impact analysis to perform this financial evaluation.

Output for this step includes the number of tolled vehicles, daily and annual revenue, and annual toll operation costs. Also bundled with this output is a set of transportation benefits calculated in monetary terms. These are presented as travel time and fuel savings as well as daily user benefits resulting from policy changes implemented on the HOV facility. Specific measures of financial feasibility and its corresponding calculation methodology are listed in Table 13. The table also presents example calculations assuming that occupancy restrictions were changed from 2+ to 3+ in the example cited previously.

Table 13: Matrix of Financial Feasibility Output

Financial Feasibility	With Selected Policy Changes
Toll Revenue and Toll O&M Cost (Only apply to Scenario with Policy Change of Pricing on Existing HOV Lanes)
Number of vehicles paying a toll in peak hours	Peak Hour Tolling Vehicle Trips (from Travel Demand Impacts) =1,252
Number of vehicles paying a toll in other Daily Periods	Daily Tolling Vehicle Trips (from Travel Demand Impacts) =15,029
Total Daily Revenue	(Total Peak Hour Tolling Vehicle Trips * HOT Peak Hour Travel Time Savings + Total Daily Tolling Vehicle Trips * HOT Daily Travel Time Savings) * Minimum Value of Time / 60 =1,241 * (49-30.4) + 15,029 * (33.6-25.5) * 25/60 = 60,341
Total Daily Revenue per Mile	Total Daily Revenue / Route Mile =60,341 / 23.9 = 2,525
Number of Working Days per Year	250 (from Parameter Page)
Gross Annual Revenue	Total Daily Revenue * Number of Working Days Per Year + Total Daily Revenue * (365 - Number of Working Days Per Year) * Ratio of Weekend Revenue and Weekday Revenue =60,341 * 250 + 60,341 * (365-250) * 0.25 = 16,820,054
Annual Toll Operation Costs	(Peak Hour Tolling Vehicle Trips + Daily Tolling Vehicle Trips) * ((Number of Working Days Per Year + (365 - Number of Working Days Per Year) * Ratio of Weekend Revenue and Weekday Revenue)) * Annual Toll Operation Cost Per Transaction) =(1,252 + 15,029) * (250 + (365-250) * .25) * .15) = 610,557
Travel Benefits (Categorized by Lane Type: HOV Lanes and GP Lanes when compared to Existing HOV Policy Scenario)
Daily User Mobility Benefits (Travel Time Savings * VOT of $/hr)	Difference on Peak Hour Total Vehicle Travel Delay (With Policy Change v.s. Existing Policy) * VOT ($/Hr) + Difference on Daily Total Vehicle Travel Delay (With Policy Change v.s. Existing Policy) * VOT ($/Hr) =(18,200 – 5,750) + (90,350 – 28,275) = 74,525
Fuel Cost Savings (Gallons)	Difference on Peak Hour Total Vehicle Travel Delay (With Policy Change v.s. Existing Policy) * Gallons of Fuel/Hour + Difference on Daily Total Vehicle Travel Delay (With Policy Change v.s. Existing Policy) * Gallons of Fuel/Hour =(728 - 230) + (3,614 – 1,131) = 2,027

Note:
HOT Peak Hour Travel Time Saving = GP Lane Peak Hour Travel Time - HOT Lane Peak Hour Travel Time
HOT Daily Travel Time Saving = GP Lane Daily Travel Time - HOT Lane Daily Travel Time

Step 4: Evaluation of Goals and Objectives

The analysis does not end with step 3. Recognizing that regional goals largely dictate transportation policy decisions, POET-ML includes an evaluation of selected policy adjustments in order to understand their ability to address common goals. The tool will employ a simple matrix that relates policy changes with common goal statements. This matrix will be populated with values that reflect the relative strength of each policy in addressing each goal. Example goals include the following:

• Protect Mobility
• Maximize person throughput
• Provide an option for travel time savings and trip reliability
• Encourage carpooling in peak periods
• Support transit service and reliability
• Manage congestion by improving system efficiency
• Improve air quality
• Provide a Financially Viable System

The user will then be able to refine the selected policy adjustment package based on this evaluation and return to the quantitative steps in the tool to reevaluate this selection. In this way, the user will be able to strike an appropriate balance between quantitative and qualitative policy acceptability.

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[1] Source: Environmental Protection Agency

December 2008
FHWA-HOP-09-031