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Transportation Performance Management


HERS-ST Highway Economic Requirements System - State Version: Technical Report - Chapter 3: Inputs

HERS' inputs are broadly divided into two groups. The first group is section-specific data which define the attributes of individual highway sections. This group can be further divided into the descriptive attributes contained in the HPMS sample section records and the prescriptive attributes contained in the user-specified improvement file. The second group consists of that wide range of parameters which are not specific to individual highway sections. This second group is further divided into control data, which govern the overall analysis, and parameter data, which is used by the internal sub-models' various processes.

This chapter also addresses the processing performed by the HERS PreProcessor. The basic function of this software is to transform the comma-delimited input file into a binary file for subsequent processing by the HERS model. It also performs some reasonableness checks, converts units and codes, calculates additional section-specific values needed by HERS, and pre-processes the user-specified improvement file.

The HERS-ST graphical user interface (GUI) functions as an intermediary between the HERS-ST user and the HERS executables and parameter files. The GUI provides tools to manipulate section data, control data, and program parameters. The GUI invokes both the PreProcessor and the HERS engine and collects the output for generation of reports, graphs, and maps. See the HERS-ST User's Guide for detailed information on using the GUI.

This chapter addresses the inputs as received by the HERS engine and the PreProcessor. It also discusses several basic HERS topics.

3.1 Section Data

Each highway section represents a potential improvement project. Whatever information HERS is provided with about the individual section (pavement condition, length, etc.) is contained in the section data for that section.

3.1.1 HPMS Sample Section Data Items

HERS accepts section data in the HPMS comma-delimited format. Although HERS does not use all the HPMS fields, the unused fields must still be marked by a comma. The individual fields should be coded as described in the HPMS Field Manual of December, 2000.

Table 3-1 presents the HPMS data items used by HERS. Each HPMS item is identified by HPMS item number. Item numbers not listed in Table 3-1 are not used by HERS. The "Editing" column may summarize edits performed by the PreProcessor or refer the reader to paragraphs describing the edit process in greater detail.

Table 3-1. HPMS Data Items Used by HERS
HPMS Item No. Variable Name Description Editing by HERSPP
1 YR Year
2 STATE State FIPS code
3 UNITS Reporting unit (English or metric) from "0=eng, 1=metric" to "1=eng, 2=metric"
4 CNTY County code Alaska conversion, see section
5 SECTIONID Section identification
8 SCF State control field
10 LRSID LRS Identification
11 BEGMP LRS beginning mile point
12 ENDMP LRS end mile point
13 RURURB Rural/urban designation HERSPP validates against FC (see
17 FC Functional class see
18 GFC Generated functional class code
20 UNBLT Unbuilt facility code section skipped if unbuilt
27 FT Facility type (one- or two-way) section skipped if structure
30 SLEN Section length metric/English conversion, see
33 AADT Annual average daily traffic
34 TLANES Number of through lanes
35 IRICOD International roughness index metric/English conversion, see; conversion to PSR, see
36 PSR Pavement condition unpaved default value, see; paved default value, see
37 HOV HOV operation code
47 SECNUM HPMS sample identifier or other section identifier
49 EXPFAC Expansion factor for standard HPMS sample
50 SURF Surface type converted to HERS codes: see
51 SNORD Structural number or Depth unpaved default, see; metric/English conversion, see; calculated, see
52 CLIMATE Climate zone
53 IMPYR Year of surface improvement
54 LANEW Lane width metric/English conversion, see
55 ACCESS Access control code
56 MEDT Median type code
57 MEDW Median width metric/English conversion, see
58 SHLDT Shoulder type code converted to HERS codes: see
59 RSHLDW Right shoulder width metric/English conversion, see
60 LSHLDW Left shoulder width metric/English conversion, see; nondivided highways, see
61 PKPARK Peak parking code
62 WDFEAS Widening feasibility code
63 - 68 LCURVE(I) Curves by class total curve length, see; metric/English conversion, see
69 HORALN Horizontal alignment adequacy code optional recalculation, see
70 TERRN Type of terrain urban code default, see
71 VERALN Vertical alignment adequacy code optional recalculation, see
72-77 LGRADE(I) Grades by class total grade length, see; metric/English conversion, see
78 PSD Percent passing-sight distance
79 WDS Weighted design speed re-calculated, see
80 SPDLIM Posted speed limit enforces maximum speed, see; metric/English conversion, see
81 PCPKSU Percent peak single-unit commercial vehicles percentage conversion, see
82 PCAVSU Percent average daily single-unit commercial vehicles percentage conversion, see
83 PCPKCM Percent peak combination commercial vehicles percentage conversion, see
84 PCAVCM Percent average daily combination commercial vehicles percentage conversion, see
85 KFAC K-Factor percentage conversion, see; validation, see
86 DFAC Directional factor percentage conversion, see; validation, see
87 PLANES Number of peak lanes
88 LTURN Turning lanes - left urban validation, see
89 RTURN Turning lanes - right urban validation, see
90 SIGTYP Prevailing signalization type code signalization validation and override, see
91 PCTGRN Percent green time percentage conversion, see; validation, see
92 NSIG Number of intersections with traffic signals enforces maximum number of traffic control devices per mile, see
93 NSTOP Number of intersections with stop signs on sample section enforces maximum number of traffic control devices per mile, see
94 NOINTS Number of other intersections
95 CAPAC Peak capacity (peak direction) optionally re-calculated, see
97 FAADT AADT in future year (FADTYR) default if zero and maximum rate, see
98 FADTYR Future year for AADT forecast default if zero, see
3.1.2 User-Specified Improvements Data File

The HERS-ST user may specify improvements to be implemented on individual sections at pre-determined times. (This capability is not available with the national version of the HERS model.) The improvements are contained in a comma-delimited text file which the PreProcessor converts to a binary file for subsequent implementation by the HERS executable. The HERS-ST GUI includes tools for generating, modifying, and maintaining the text file, or users may elect to construct it manually.

The input file consists of a variable-length record for each section being improved. Table 3-2 shows the nine fields which comprise the file. The first field declares the number of improvements defined for the section (and thus the length of the record). The second and third fields identify the section, and correspond to HPMS input fields 4 (County) and 47 (Sample ID). The fourth through ninth fields pertain to an individual improvement, and are repeated for each improvement defined for the section. (Thus, a record which specified two separate improvements would consist of fields 1 through 3, then 4 through 9 to define the first improvement, and 4 through 9 again defining the second improvement.)

Table 3-2. User-Specified Improvement Input Fields
Field GUI Column Name Format
1. Number of Improvements Improvements integer
2. County Code County integer
3. Sample Identifier SampleID alphanumeric
4. Year of Improvement SFn_Year integer
5. Type of Improvement SFn_ImpTyp integer
6. Override Flag SFn_Ovrd integer
7. Cost of Improvement SFn_ImpCst floating point
8. Lanes To Add SFn_LaneAdd integer
9. Increase in Capacity SFn_IncCap integer

3.2 HERS Control and Parameter Variables

In addition to the section-specific data files, HERS and the HERS PreProcessor accept three additional files of processing parameters plus two files containing control variables. Broadly speaking, the two control files (one each for HERS and the PreProcessor) contain processing directives which are likely to be specific to an individual analysis run, while the parameter files contain data which are more likely to be unchanged between runs. The HERS-ST GUI does not require the user to be aware of these separate control files when operating the GUI under standard mode, and presents the various control parameters to the user without indicating that they belong to individual files controlling distinct programs.

Two of the parameter files are focused on specific themes. The improvement cost file (IMPRCOST.DAT) contains data items which define the costs of improving highway sections: its contents are discussed below and their use is explicated in Chapter 6. The deficiency level tables file (DLTBLS.DAT) defines the various condition levels which will prompt HERS to analyze a section for possible improvement. Chapter 4 discusses the use of these criteria, which are listed, with their default values, in Appendix A, "Default Deficiency Criteria Tables." The third parameter file (PARAMS.DAT) contains parameters covering the breadth of the HERS modeling process: the pavement model, operating cost components, the speed model, and the safety model, to name but a few. This report addresses these specific parameters when discussing the various internal models and processes.

3.2.1 The Preprocessor Control Inputs

Table 3-3 presents the inputs to the PreProcessor. These are passed in the file PPSPEC.DAT. The columns in the table are:

  • Control Input - the acronymic name of the data item;
  • Available via GUI - whether or not the data item is presented to users of the HERS-ST GUI using standard mode (all data items are available using advanced mode); and
  • Description - a brief description of the input and a reference to further reading.
Table 3-3. PreProcessor Control Inputs
Control Input Available via GUI? Description
a. Although the user does not specify the name of the file, selects the file from those available within the current project.
FILIN Noa Name of section data file (see section 3.1.1)
FILOUT No Binary section file name
DSTOUT No Distribution file name
HPMSF No HPMS format flag
BASEYR Yes Base year of analysis
PSRUPS Yes PSR for unpaved sections (see; passed to HERS as lower limit of pavement deterioration.
CALCCAP No Coded capacity override switch (see
MAXGRW Yes Maximum AADT growth rate (see
GRSWITCH No Governs treatment of excessive growth rate (see
DEFGRW No Default AADT growth rate (see
PGTMAX No Maximum percent green time (see
PGTMIN No Minimum percent green time (see
PGTRUR No Table of default percent green time (see
MAXR Yes Maximum AADT/Capacity ratio (see
MRERR Yes Report excessive AADT growth rate switch
MAXTCD No Maximum number of traffic control devices per mile (see
NTDERR No Governs generation of traffic control device error messages
MAXSPL Yes Maximum speed limit
RUERR No Governs generation of FC and RURURB error messages
AASWITCH No Alignment adequacy calculation switch (see
PLERR No Peak lanes error reporting switch
PSRIRI Yes PSR/IRI selection switch
OVERIDEMODE Yes Implement user-specified improvements switch
STATEIN Noa Name of user-specified improvement file
STATEOUT No Name of binary user-specified improvement file
3.2.2 The HERS Control Inputs

Table 3-4 presents the inputs to the HERS executable. These are passed in the file PPSPEC.DAT. The columns in the table are the same as for the PreProcessor inputs of Table 3-3.

Table 3-4. HERS Control Inputs
Control Input Available via GUI? Description
a. The HERS-ST GUI provides control over a subset of the text output pages.
RUNNUM Yes Sixteen character run identifier
RUNDES Yes Run description
FILOVR No Input file overwrite switch
FILDEL No End-state file deletion switch
FILIN No Binary section file name
STATEIMPS No Binary user improvement file name
DISTIN No Distribution file name
FILOUT Yes Output text file name
LFP Yes Length of funding period
NFP Yes Number of funding periods
AADTTY Yes Type of AADT growth
INPUTLRS Yes Long run share of elasticity
INPUTSRE Yes Short run elasticity
DRATE Yes Discount rate
BACKLG Yes Backlog switch
IMPRST Yes Governs printing of user improvement information
WARNMSI No Governs user improvement warning message generation
WARNMSG No Directs user improvement warning messages
MAXNTD No Maximum number of traffic control devices per mile
MNDIMP Yes Mandatory improvement switch
NEEDS Yes Full engineering needs switch
BCRMIN Yes Minimum BCR
OBJCTV Yes Analytical objective
MCC Yes Maintain current conditions switch
CSPEC Yes Constraint specification selector
SCVALU Yes Table of fund/performance constraints
NMFNDS Yes Table of funds reserved for non-mandatory improvements
AIUNIT Yes Units of funds for aggressive improvements
CWT Yes Constraint weights
MCUNIT Yes Maintenance cost units
BCRWT No Benefit-cost ratio weights
OUTPUT Yesa Table selects output text pages
SCFACT Yes Output scale factors
PPDUNITS No Peak period delay units
NPSEC No Sections processed interval
NSIMP No Improvements selected interval
3.2.3 Parameter Inputs

HERS uses three input parameter files, one each for improvement costs, deficiency levels, and general parameters. The PreProcessor uses the deficiency levels file and the general parameter files. The GUI ensures that the same files used for the PreProcessor are used for the main HERS program. IMPRCOST.DAT - the Improvement Cost File

HERS uses the costs in this file to calculate the cost of section improvements. All the fields of this file are available through the GUI.

The file consists of one column for each of the nine elemental improvement costs, and twenty-one rows corresponding to highway group. Table 3-5 presents the elemental cost columns.

Table 3-5. Elemental Improvement Cost Columns
Column Column Label Improvement Cost
A RECON W-LAN Cost to reconstruct and widen existing lanes
B RECON PAVE Cost to reconstruct existing lanes
C RESURF W-LAN Cost to resurface and widen existing lanes
D RESURF PAVE Cost to resurface existing lanes
E IMPRV SHLD Incremental cost to improve shoulder (one side)
F ALANE NORM Incremental cost to add lane at normal cost
G ALANE HIGH Incremental cost to add lane at high cost
H ALGN NORM Cost to realign all lanes at normal cost
I ALGN HIGH Cost to realign all lanes at high cost

For calculation of improvement costs, HERS uses seven highway classifications, each of which is subdivided into three groups. The four rural classifications correspond to the four rural functional classes:

  • Interstate;
  • Other Principal Arterial;
  • Minor Arterial; and
  • Major Collector.

Within each rural classification sections are further divided by terrain type:

  • Flat;
  • Rolling; or
  • Mountainous.

Urban sections are divided into three classifications:

  • Interstate and Principal Arterials - Other Freeways and Expressways;
  • Other Principal Arterials; and
  • Minor Arterials and Collectors.

Within each of these urban classifications, sections are divided by urbanized area:

  • Small Urban;
  • Small Urbanized; or
  • Large Urbanized.

See Chapter 6 for details of how HERS calculates the costs of improvements. DLTBLS.DAT - the Deficiency Levels File

The DLTBLS.DAT file contains deficiency and design standard parameters. It also contains user-specified thresholds used in generating output statistics. Table 3-6 presents the deficiency level entries from the beginning of the DLTBLS.DAT file.

As indicated in Table 3-6, the deficiency level and user-specified threshold entries (DL and UST1) are available via the GUI (on the Deficiency Thresholds page of the Parameter Data interface). The remaining items can be accessed through the Advanced Mode.

For the categories shown in Table 3-6, the rural sections are differentiated by functional class, terrain type, and (except for Interstates) by volume groups. Urban sections are differentiated by functional class except for the two alignment categories: for horizontal alignment, HERS requires entries for Interstates, Other Freeways, and OPAs; there are no entries for urban vertical alignment. Also, there are no design standard (DS) entries for urban sections for these three categories: surface type, lane width, and right shoulder width - they are included in the second part of DLTBLS.DAT where the sections are grouped differently.

Table 3-6. Deficiency Level Tables in DLTBLS.DAT
Attribute and (Units) Deficiency Level Column Headings Available through GUI? Description
Pavement Condition (IRI) UST1 N User Specified Thresholds used for output statistics only
Pavement Condition (PSR) UL N Unacceptability Level
RL N Reconstruction Level
UST1 Y User Specified Threshold used for output statistics only
UST2 N User Specified Threshold used for output statistics only
DL Y Deficiency Level
Surface Type (HERS Surface Type codes; see UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level
DS N Design Standard
V/C Ratio (V/C Ratio) UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level
WS N Widening Standard
Lane Width (feet) UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level
DS N Design Standard
Right Shoulder Width (feet) UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level
DS N Design Standard
Shoulder Type (HERS Shoulder Type codes, see UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics and minimum shoulder type after reconstruction
DL Y Deficiency Level
Horizontal Alignment (HPMS Horiz. Alignment Adequacy Code) UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level
Vertical Alignment (HPMS Vert. Alignment Adequacy Code) UL N Unacceptability Level
SDL N Serious Deficiency Level
UST1 Y User Specified Threshold used for output statistics only
DL Y Deficiency Level

The second part of the DLTBLS.DAT file contains additional design standard entries. These entries are available through the GUI using the Advanced Mode. The entries in this second part of the file are presented in Table 3-7.

Table 3-7. Additional Design Standards in DLTBLS.DAT
Design Standard Units Rural Section Groups Urban Section Groups
Curve Categories HPMS Curve Classes By functional class by terrain By Interstate, Other Freeway, and OPA
Grade Categories HPMS Grade Classes By functional class by terrain (None)
Lane Width Feet (None) By Freeway/Expressway by Design; Other Divided; Undivided Arterials; and Undivided Collectors
Shoulder Width Feet (None) By Freeway/Expressway by Design; Other Divided; Undivided Arterials; and Undivided Collectors
Surface Type HERS Surface Type code (None) By Freeway/Expressway by Design; Other Divided; Undivided Arterials; and Undivided Collectors

For the discussion of HERS' use of deficiency criteria, see paragraphs 4.2.1 and 4.2.2. The application of design standards to improved sections is addressed in paragraph 4.2.4. PARAMS.DAT - the Parameter File

The PARAMS.DAT file contains the balance of HERS input parameters. The first two lines are used to identify the specific file. The bulk of the entries are grouped into ten topics, each of which is addressed below. These in turn are followed by several groups of arcane parameters (beginning with TRISF, the travel rate index scale factor) which apply only to the national version of the model, have no effect on the operation of HERS-ST, and so are not described here.

Only a few of the parameters in PARAMS.DAT are available through the GUI. Unless specifically noted in the text, these parameters can only be modified using Advanced Mode. Pavement Improvement Parameters

This is a loosely focused set of parameters which appear in two locations in the file: at the very beginning (right after the file identification) and further down under the heading "For PAVIMP subroutine." Most of the parameters available through the GUI are part of this group. These parameters are:

  • DP - Design period, in years, available through the GUI;
  • WDFOVR - Widening feasibility override, specified for each functional class using the widening feasibility codes (see Table 4-8), available through the GUI;
  • MAXLNS - Maximum number of lanes, by functional class, available through the GUI;
  • PAVMTH - Thickness of new pavement, in inches, by ESAL range limits (from RNGLIM entries) for a) all reconstruction or resurfacing of flexible pavement, and b) resurfacing of rigid pavement;
  • PSRREC - PSR after reconstruction, for each of four pavement types (high flexible, high rigid, medium, and low) for rural and urban, available through the GUI;
  • PSRINC - Increase in PSR after resurfacing, for each of four pavement types (high flexible, high rigid, medium, and low) for rural and urban, available through the GUI;
  • PSRRMX - Maximum value of PSR after resurfacing, for each of four pavement types (high flexible, high rigid, medium, and low) for rural and urban, available through the GUI;
  • RNGLIM - Range limits for design number of ESALs, in thousands of ESALs, five entries defining six ranges; and
  • NEWSNC - Coefficients for calculating new structural number (SN) after improvement using Equation 4.1. Truck Growth Factors

This three line entry specifies the annual growth rate of trucks as a portion of total traffic on all sections in each functional class. The factor is applied to the average percent of single unit trucks and the average percent of combination trucks (HPMS data items 82 and 84) when forecasting future traffic volumes. This factor does not directly affect the traffic volume, but only the average percentages of the two truck groups.1 Operating Cost Parameters

This section of PARAMS.DAT establishes values for the five components of operating costs:

  • fuel consumption
  • oil consumption
  • tire wear
  • maintenance and repair
  • depreciable value.

The section contains two sets of entries. The first set specifies the Efficiency Adjustment Factors for each of the components. These entries represent changes in the consumption of resources by the vehicle fleet since 1980. See paragraph, "Adjustment Factors for Consumption Rates," for a detailed discussion.

The second set of entries is for the unit prices of the five components. These are discussed in paragraph, "Component Prices."

For both sets of entries, HERS requires separate values for each of the seven vehicle types. Fuel Excise Tax Parameters

This short section begins with entries of the fuel tax for each of the seven vehicle types. Entered in dollars per gallon, this is the fuel tax at the beginning of the analysis period. The next four lines are for factors altering the fuel tax during the course of the analysis beginning with the first funding period. Speed and Congestion Parameters

These parameters are found in two places in the PARAMS.DAT file. The first group is designated as "For APLVM subroutine," the second group is near the end of the file and is labeled "For CONGFWAY and CONGSigArt subroutines."

The APLVM group consists of variables HERS uses to calculate the effect of pavement roughness on speed, as presented in paragraph The four input values are:

  • VR1 - Speed limited by roughness at PSR of zero;
  • VR2 - Speed limited by roughness when PSR is equal to PSRB;
  • PSRB - PSR value above which the speed limited by roughness is determined by VRSLOP; and
  • VRSLOP - Slope of speed limited by roughness above PSRB.

1. Note that the change in traffic composition may have a small effect on volume due to the application of demand elasticity.

The congestion group consists of three entries:

  • BPM - Bottlenecks per mile, one value each for freeways and signalized arterials;
  • INCFAC - incident rate factor to reflect the effects of policy to reduce incident rates, one value each for freeways and signalized arterials; and
  • SIGADJF - Signal timing adjustment factor, four values corresponding to the four SIGTYP codes. Price Indices

The price indices are the mechanism used to align various input values, expressed in dollars of a specific year, with the single dollar-year HERS uses to perform its cost, benefit, and price calculations. This is typically the base year of the analysis period corresponding to the description of the highway system contained in the section data file. Although HERS discounts future benefits and costs using the user-supplied discount rate (DRATE), HERS does not support fluctuations in the value of the dollar but conducts all evaluations using constant dollars.

There is a wide variety of dollar-valued inputs to HERS (improvement costs, vehicle maintenance costs, costs of crashes, etc.) which are specified in a wide range of dollar-years. This is sometimes a reflection of the data used in the original research that became the basis for the model incorporated into HERS, and sometimes of the most recent publication of the statistics used to generate the HERS inputs.

Table 3-8, "Price Indices Used by HERS," presents a list of sources used in indexing HERS prices and costs on a national basis. Pavement Deterioration Parameters

These parameters, labeled in the file as belonging to the FORCST routine, affect the model's calculation of pavement deterioration. This first group of parameters affects the limits of the PSR deterioration procedure.

  • PDRAF - The pavement deterioration rate adjustment factor, entered separately for rigid and flexible pavements, is a gross adjustment applied to the deterioration due to accumulated ESALS.
  • MAXPD - The maximum pavement deterioration rate, entered in PSR per year, places an upper limit on the rate of pavement deterioration.
  • MAXLFE - The maximum pavement life, entered by pavement section and rigid/flexible pavement, is used in enforcing a lower limit on pavement deterioration (that is, in ensuring that pavement deteriorates enough each year that it will not outlive its maximum projected life).

HERS uses the second group of parameters in calculating the effect of accumulated ESALS on pavement deterioration.

  • SO - Prediction error, for flexible and rigid pavements;
  • REL - Reliability factor, for interstate, other arterials, and collectors;
  • MR - Modulus of resistance;
  • PT - Design terminal serviceability index;
  • SCP - Modulus of rupture;
  • CD - Load transfer coefficient;
  • J - Drainage coefficient;
  • EC - Modulus of elasticity; and
  • K - Modulus of sub-grade reaction.
Table 3-8. Price Indices Used by HERS
Parameter Nominal Base Year PARAMS.DAT Applicable Index
Price Index Line
Cost of Fuel 2002 Cost of Fuel 45
Cost of Oil 1995 Cost of Oil 46
Cost of Tires 1995 Cost of Tires 47
Cost of Maintenance 1995 Cost of Maintenance and Repair 48
Depreciable Value 1995 Cost of Vehicle 49
Fuel Excise Tax 2002 Fuel Excise Tax 50
Rural Improvement Costs 2002 Improvement Costs, Rural 51
Urban Improvement Costs 2002 Improvement Costs, Urban 52
Highway Maintenance Costs - internal (see Table 5-31, "Maintenance Costs for Flexible Pavements") 1988 Highway Maintenance Costs, Rural and Highway Maintenance Costs, Urban 53 and 54 Office of Program Administration, Price Trends for Federal-Aid Highway Construction, U.S. Department of Transportation, Federal Highway Administration, Washington, D.C., quarterly
2000 Value of Time 55
1995 Vehicle Costs 56
2000 Inventory Costs 57
2001 Value of Life 58
2000 Injury Costs 59
2000 Property Damage Costs 60
2000 Crash Delay Costs 61

See paragraph 5.1.2, "Pavement Condition," for details and usage of these parameters. Safety Parameters

The input parameters used by the safety model consist of three groups: dollar-valued damage parameters; fatality and injury to crash ratios; and parameters defining the physical properties of sections.

It's a good idea, when changing these dollar-valued parameters, to note the year of the dollar used in the comment portion of the file:

  • VLIFE - Value of life, used in conjunction with fatalities;
  • INJCST - Injury cost, for each functional class;
  • PROPDM - Property damage, for each functional class.

The crash ratios correspond to a specific year, and can be set to decline:

  • FATR - Fatality/crash ratio by functional class, govern the number of fatalities per crash;
  • INJR - Injury/crash ratio by functional class, specifies the number of injuries per crash;
  • FICRYR - Specifies the base year for the ratios;
  • APDFPC - Annual percentage decline in fatalities in per crash beginning in FICRYR;
  • APDIPC - Annual percentage decline in injuries per crash beginning in FICRYR; and
  • APDCR - Annual percentage decline in crash rates beginning in 1995.2

The following safety parameters relate to the physical characteristics of sections:

  • DDRML - Driveway density for rural multilane sections;
  • RHRRML - Roadside hazard rating for rural multilane sections;
  • MAXIML - Maximum number of intersections per mile on rural multilane sections;
  • MINSPM and MAXSPM - Minimum and maximum number of signals per mile on urban multilane sections; and
  • PDEVEL - Probability that rural road is in area of dense development, entered for three road types: two lane, multilane undivided, and multilane divided.

All of the following parameters relate to the physical characteristics of rural two lane sections, and follow the "For R2LANE subroutine" heading in the file:

  • DD - Driveway density;
  • MAXIR2 - Maximum number of intersections per mile;
  • CCGR - Crest curve grade rate, entered for each of the three terrain types: level, rolling, and mountainous (as per HPMS item number 70);
  • RHR - Roadside hazard rating;
  • RHR3LI - Roadside hazard rating for three-legged intersections;
  • PRTL - Probability that a three-legged intersection has a right turn lane; and
  • ADJIA - Adjusted intersection angle.

2. The crash rates are hardcoded and reflect 1995. Travel Time Cost Parameters

Under the heading "For TTCOST subroutine" are five entries HERS uses to determine the cost of travel time per hour:

  • TTCPPH - Travel time cost in dollars per person hour, entered for each of the seven vehicle types (see paragraph 2.11, "The Fleet Composition Model");
  • VDEPPH - Hourly vehicle depreciation costs, entered for each vehicle type;
  • INVCPH - Inventory cost per hour, with entries for each vehicle type3;
  • AVO - Average vehicle occupancy, entered for each vehicle type; and
  • DINCCR - The ratio of the value of incident delay to the value of travel time, this entry (when greater than one) exacts an additional travel time penalty when traffic is slowed due to crashes.

For more detail, see paragraph 5.5, "Travel Time Costs." State Cost Factors

The section of state cost factors in PARAMS.DAT breaks with the usual format of the file in which the parameter values are at the left of the line and the descriptive comments are on the right of the line. This section presents four columns, of which only the second (SCF for state cost factor) is a parameter value, and the other three (FIPS code, Region, and State) are not read by the model. The SCF is used to accommodate differences between the national average improvement costs and the prevailing cost of improvements in each state or jurisdiction.

3.3 The HERS Preprocessor

The HERS PreProcessor is a separate program which prepares the HPMS section record data for processing by the HERS program proper. The PreProcessor's primary functions are

  • Perform validation checks on specific fields of the HPMS input data;
  • Provide default values when the input data is missing or inappropriate;
  • Alert user to sections with values beyond specified bounds;
  • Convert certain HPMS codes to HERS codes;
  • Convert, as indicated, metric units to English units of measure, and IRI to PSR;
  • Calculate section-specific values needed by HERS but not present in the HPMS data;
  • Process user-specified improvements for implementation by the HERS model;
  • Produce two binary output files (one of section data, the other of user-specified improvements) for use by the HERS model.

3. The supplied values for inventory costs are set to zero for all vehicle types except for combination trucks.

HERS-ST users do not interface directly with the PreProcessor: the HERS-ST GUI invokes the PreProcessor automatically prior to executing the main HERS program. The HERS-ST GUI prepares the inputs for the PreProcessor from the control, parameter, highway, and improvement models specified by the user.

3.3.1 Validations

The HERS PreProcess corrects input data that shows invalid or inconsistent codes. Sections Skipped by HERSPP

HERSPP "skips" certain sections by not writing a section record to the binary file for use by HERS. HERSPP skips the following sections:

  • Local sections (with generated functional class code set to 6)4;
  • Rural minor collectors (functional class code equal to 8)4;
  • Unbuilt sections (when the Unbuilt field is greater than 1);
  • Structures (when the facility code is greater than 2);
  • Sections with the rural/urban designation input as zero;
  • Sections with the functional class input as zero;
  • Sections with the section length input as zero;
  • Sections with the initial AADT input as zero; and
  • Sections with the expansion factor input as zero.

HERSPP reports the number of sections skipped. RURURB Validation

HERSPP checks the Rural/Urban designation against the functional class. If a section's functional class code is greater than 10 and the rural/urban designation is set to 1 (rural area), it is reset to 4 (large urbanized area). If a section's functional class code is less than 10 and the rural/urban designation is greater than 1, it is reset to 1. Functional Class Validation

If a section's functional class (FC) is input as 13 or 15, HERSPP resets the FC to 12 or 14, respectively.

4. The HERS-ST GUI resets the functional class codes for these sections to either rural major collectors or urban collectors, as appropriate, before passing the section data to the PreProcessor.

If a section's FC remains invalid, and the generated functional class code (GFC) and rural/urban designation are valid, then HERSPP sets the FC as shown in Table 3-9.5

Table 3-9. Imputing Functional Class
If Generated Functional Class is: And Rural/Urban Designation is: Then the Functional Class Code Assigned is:
1 - Interstate 1 (rural) 1 - Principal Art. - Interstate
2 - Other Principal Arterial 2 - Principal Art. - Other
3 - Minor Arterial 6 - Minor Arterial
4 - Major Collector 7 - Major Collector
5 - Minor Collector 8 - Minor Collector
1 - Interstate 2, 3, or 4 (urban) 11 - Principal Art. - Interstate
2 - Other Principal Arterial 12 - Principal Art. - Other Freeways and Expressways
3 - Minor Arterial 14 - Principal Art. - Other
4 - Major Collector 16 - Minor Arterial
5 - Minor Collector 17 - Collector Maximum Traffic Growth Rate

The PreProcessor calculates the traffic growth rate for the section based upon the initial and future AADT values (for details, see paragraph

If the growth rate is greater than the maximum growth rate specified by the user in MAXGRW, HERSPP performs the corrective action (one of two) specified by the user in GRSWITCH. The user may specify that HERSPP use the growth rate entered in DEFGRW. (This is the option in effect when running the HERS-ST GUI, which sets DEFGRW to MAXGRW before invoking the PreProcessor.)6 Or the user may instruct HERSPP to display an error message identifying the section and prompt the user to manually enter a growth rate for the section. In either case, HERSPP continues by adjusting the section volume parameters to reflect the new growth rate. Curves and Grades

HERSPP examines the curve and grade classes in each input record to ensure that the total length of reported grades/curves equals the length of the section. HERSPP uses the same validation process for both curves and grades. First, HERSPP totals the lengths of the reported curves/grades. If the reported lengths total less than the section length, HERSPP checks the length reported for the lowest curve/grade class. The lowest class includes those portions of the roadway which have neither curves nor inclines. If the reported length of the lowest class is zero, HERSPP assigns the unreported length to the lowest class. If the reported length of the lowest class is not zero, HERSPP scales the lengths of all the curve/grade classes to total the section length.

If the total reported curve/grade lengths are longer than the section length, HERSPP checks whether the length of any single curve/grade class is greater than the section length. If so, and the sum of the lengths of the remaining classes is less than the section length, then HERSPP sets the length of the longest class to the difference between the total length of the other classes and the length of the section. Otherwise, HERSPP scales the lengths of all classes to total the section length.

5. The astute reader will note that one of the possible functional classes assigned by HERSPP is Rural Minor Collectors, which is not normally processed by HERS. That this logic was unchanged when Rural Minor Collectors were removed from the HPMS database was an oversight.

6. YO! Should call Tevin/Tom and confirm that this is what it does! Speed Limit

HERSPP enforces the maximum speed limit specified by the user in the PPSPEC file. It also enforces a minimum speed limit of 15 miles per hour, and sets the limit to the nearest multiple of 5 mile per hour. K and D Factors

If the K-factor is set to zero, HERSPP sets it to 0.1.

HERSPP converts the directional factor entry into a fraction by dividing the integer entry by 100. If the subsequent value is between 0.05 and 0.1 (indicating five and ten percent, respectively) HERSPP assumes an entry error and multiplies the value by ten (setting it between fifty and one hundred percent). Then, if the directional factor is less than fifty percent (0.5), HERSPP sets it to fifty percent and examines the facility type (Item 27). If the section is one-way, it sets the directional factor to 100 percent.7 Percent Green Time

On sections with traffic signals, HERSPP checks to ensure that a value is entered for percent green time (Item 91). If the entered value is zero, HERSPP issues an informative error message and sets the variable to one of the values specified by the user in PGTRUR, as shown in Table 3-10.

Table 3-10. Percent Green Time Default Value Selection
Functional Class PPSPEC Entry Used
Rural Interstate First entry on line 26
Rural Principal Arterial - Other
Urban Interstate
Urban Principal Arterial - Other Freeways or Expressways
Urban Principal Arterial - Other
Rural Minor Arterial Second entry on line 26
Urban Minor Arterial
Rural Major Collector Last entry on line 26
Urban Collector

HERSPP also enforces the user-specified maximum and minimum percent green time limits entered by the user in the PPSPEC.DAT file. Traffic Control Devices per Mile

The PreProcessor limits the number of traffic control devices (stop signs and traffic signals) per mile to the maximum specified by the user in PPSPEC.DAT (MAXTCDS). Turning Lanes

HERSPP examines urban sections with intersections. If the code for either the left or right turn lanes (Items 88 and 89) are zero (rural section or section without intersections), it resets the code to four (turns permitted; no exclusive turning lanes exist). Signalization Validation and Override

HERSPP passes a single value for type of signalization to the HERS-ST analytical engine. HERSPP examines the signalization type override field (SIGTYPOVERIDE) and if it is a valid signalization code (that is, from one to four), it copies that value to the output record. If the SIGTYPOVERIDE value is not from one to four, HERSPP then validates the SIGTYP field: if SIGTYP is less than one or greater than three HERSPP sets the field to one.

Note that HERSPP only examines the SIGTYP field when the SIGTYPOVERIDE field does not specify an override value. Set SIGTYPOVERIDE to zero to ensure that the SIGTYP field is enabled. Note also that while the validation sequence imposes a default value of one (uncoordinated fixed time) for sections with enabled SIGTYP entries of zero (rural sections not reporting signalization) and four (no signal systems exist) as well as for sections with invalid SIGTYP entries, the signalization field will not be referenced by the HERS-ST analytical engine for sections without traffic signals.

7. YO - only checks FT if DFAC < 50%, so HERSPP does not correct for a one0way facility with a DFAC between 50 and 99%. Check w/ Herb for specific reason, or oops.

3.3.2 Default Values

For selected data items, the HERSPP will substitute a default value for missing data. Default Values for Unpaved Sections

HERSPP assigns the following values to all unpaved sections:

  • PSR is set to the user-specified value from PPSPEC.DAT;
  • SNorD is set to zero;
  • Pavement section is set to zero; and
  • Accumulated ESALs is set to zero. Other Default Values

For sections with input PSR and IRI of zero, or a PSR value greater than 5.0, HERSPP assigns the default PSR value of 3.2.

HERSPP sets the left shoulder width for all non-divided highways to zero.

HERS requires a positive terrain code (1, 2, or 3) for all sections. The HPMS Field Manual specifies that urban sections be assigned a terrain code of zero. HERSPP changes all terrain code entries of zero to one.

3.3.3 Calculated Values

The PreProcessor calculates a number of values from the input section data. In some cases these values may supply data not included for a particular section. In other cases, the PreProcessor replaces the input data. In most cases the PreProcessor is calculating data needed by HERS but not included in the input data. SN or D

For paved sections without an input value for SN or D (SNORD, that is, Structural Number or Depth), HERSPP calculates an initial value based upon annual ESALS. HERSPP first calculates the annual ESALS based upon the reported traffic volume:

Eq. 3.1



AESALS = annual ESALS;
AADT = daily traffic (from HPMS input);
LANFAC = lane adjustment factor;
PCAVSU = percent average single unit trucks (from HPMS input);
PCAVCM = percent average combination trucks (from HPMS input); and
EALFAC = ESAL adjustment factor, for single unit and combination trucks.

The lane factor adjusts for the number of lanes (in one direction) on the section. The ESAL factor adjusts for the functional class, type of overlay, and truck class. (For a more detailed discussion, see paragraph section 5.1 "The Pavement Deterioration Model" on page 5-1 which presents the ESAL and lane adjustment factors in Table 5-1 and Table 5-2, respectively.)

Next, HERSPP imputes SNORD based upon the number of annual ESALS and the type of surface. For high type rigid pavements, HERSPP calculates:

Eq. 3.2

SNORD = 5.51 × AESALS0.0383

For other pavements, HERSPP calculates:

Eq. 3.3

SNORD = 0.979 × AESALS0.1159 Pavement Section

HERSPP assigns a pavement section (PAVSEC) value for each section for use by HERS. The value of PAVSEC is based upon the value of SNORD, as shown in Table 3-11.

Table 3-11. Assigning PAVSEC Values
Rigid Pavement Flexible Pavement Pavement Section (PAVSEC)
SNORD <= 7 SNORD <= 3 5 (Light)
7 < SNORD <= 9 3 < SNORD <= 4.5 4 (Medium)
9 < SNORD 4.5 < SNORD 3 (Heavy) ESALs Prior to the Base Year

HERSPP calculates the cumulative number of ESALs on each section at the beginning of the analysis period; that is, the number of ESALs needed to bring about the section's initial PSR. Sections with PSR of 5.0 or greater are considered new with zero accumulated ESALs. HERSPP begins the calculation by computing the intermediate variables XA and XB. For flexible pavements, HERSPP uses:

Eq. 3.4

SNA = SN + (6/SN)

Eq. 3.5

XA = 9.36 × log(SNA) 0.2

Eq. 3.6

XB = 0.4 + 1094/SNA5.19

where SN is the structural number.

For rigid pavements, HERSPP uses:

Eq. 3.7

XA = 7.35 × log(D + 1) 0.06

Eq. 3.8

XB = 1 + 16.24 × 106/(D + 1)8.46

where D is pavement thickness.

HERSPP next calculates the variable XG:

Eq. 3.9

XG = log((5 PSRI)/3.5)

where PSRI is the PSR at the beginning of the base year.

Finally, HERSPP calculates ESALs accumulated on the section prior to the base year:

Eq. 3.10

ESAL = 10(XA + XG/XB) Time and PSR of Last Pavement Improvement

For unpaved sections, HERSPP designates the original (input) PSR as the PSR after last improvement (PSR0), and sets the year of the last pavement improvement (IMPYR) negative to indicate that there was no such improvement.

For paved sections, HERSPP uses the year of last surface improvement (Item 53) if supplied, or else the midpoint of the year preceding the base year. PSR after the last improvement is set to the lesser of the initial PSR or the user-specified maximum value of PSR after resurfacing (PSRRMX).8 Weighted Design Speed

HERSPP discards the input weighted design speed (WDS, Item 79) and recalculates it for all sections. The weighted design speed will be used by HERS to determine maximum service flow during capacity calculations on rural and urban multilane sections.

HERSPP follows the procedures outlined in Appendix M of the HPMS Field Manual (December 2000) for estimating weighted design speed on sections with and without reported curve data.9 Capacity

The PreProcessor calculates the section's base capacity plus peak, off-peak, and counterpeak capacities for the section (see section 4.4.1 "Capacity" on page 4-30 for details). The Preprocessor also sets the section's capacity ratio (CRATIO) variable depending upon the value of the input CALCCAP.

If CALCCAP is set to zero (the default case), the three capacity estimates are calculated from the section's input value for base capacity. (If no capacity was coded for the section, the Preprocessor calculates the base capacity.) The Preprocessor then sets CRATIO to the coded capacity divided by the calculated base capacity. This identifies sections whose conditions result in capacity different from that calculated by the HCM procedures. HERS assumes that the factors which determine the capacity difference are not reflected in the section's geometric data items, and captures the ratio of the difference in CRATIO. When recalculating the section's capacity after improvement, HERS further assumes that the unknown factors affecting capacity are still in effect, and uses CRATIO to maintain the ratio between the effective and calculated section capacities.

8. Nonetheless, HERS v. 3.5.4 subsequently references neither of these parameters.

9. The sole variation is on non-multilane sections without curve data. For these, HERSPP calculates weighted design speed as if the section were multilane. This is acceptable because HERS will only use weighted design speed if it considers adding lanes to the section, in which case it will become a multilane section.

If CALCCAP is set to one, HERS uses the calculated base capacity as the basis for estimating the trio of peak capacities. It then replaces the coded base capacity with the calculated capacity and sets CRATIO to one.

HERSPP also checks to ensure that the ratio of daily volume to capacity (AADT/Capacity) is less than the maximum ratio specified in MAXR. If it is greater than the specified maximum, HERSPP increases the section's capacity until it meets the MAXR limit. HERSPP then sets CRATIO using the increased capacity. Traffic Growth Rates

HERSPP uses the initial and forecast traffic volumes from the input record to compute growth rates for the section.

HERS provides the user with the flexibility to project baseline traffic using one of several options, each reflecting different travel growth characteristics. Parameters for each option are initialized by the PreProcessor, and are determined so that, were no elasticity applied, traffic volume on the section would reach the specified Future AADT value at the Future AADT Year. Option One is for concave geometric growth, Option Two is for linear growth, and Option Three provides for convex geometric growth, as shown in Figure 3-1.

Figure 3-1. Travel Growth Options
Figure 3-1. Travel Growth Options

The example in Figure 3-1 is of a section with an initial AADT of 5000 in data year 1990. The future AADT year is 2010, at which time the AADT will have grown to 10,000. The growth rate is calculated for each section based upon the data in its HPMS record. The trend lines show baseline traffic volume without the application of demand elasticity. The linear growth method (option Two) was used for the 1997, 1999, and 2002 editions of the C&P Report. Option One - Concave Geometric Growth

The geometric option projects baseline traffic by applying a constant rate of growth throughout the analysis period. Because the volume of additional traffic each year is based upon the previous year's volume, more vehicles are added each year. The Pre-Processor calculates the growth factor, AADTGR:

AADTGC equals FAADT divided by AADT all raised to 1 divided by quantity FAADTYR minus AADTYR


AADTGR = constant growth rate;
FAADT = Future AADT from HPMS section record;
AADT = current AADT from HPMS section record;
FAADTYR = year of Future AADT from HPMS section record; and
AADTYR = year of current AADT from HPMS section record.

AADT for any time t1 may be projected along a concave curve:

Eq. 3.12

AADTt1 = AADTt0 × AADTGR(t1 t0)

AADTt0 = known AADT at time t0. Option Two - Linear Growth

The second option applies a linear, or constant, growth function throughout the period, so that the same number of vehicles are added each year. The growth factor (AAGRSL) is calculated by the PreProcessor:

Eq. 3.13


AAGRSL = straight line growth rate.

Using the linear growth function, AADT is projected:

Eq. 3.14

AADTt1 = AADTt0 + AAGRSL × (t1 t0)

This is the growth option used for the 1997, 1999, and 2002 versions of the C&P Report. Option Three - Convex Geometric Growth

In the third option, the geometric and linear models are combined to project growth along a convex curve. This curve is the mirror image of the concave geometric curve relative to the linear growth function, and provides for rapid initial growth followed by less aggressive growth. Future AADT at time of interest t1 is calculated:

Eq. 3.15

AADTt1 = 2 × AADTt0 + AAGRSL × (t1 t0)) AADTt0 × AADTGR (t1 t0) Additional Growth Rate Considerations

If the input future volume FAADT is zero, HERSPP sets FAADT to the initial volume (AADT) and assumes a zero growth rate. If the future year FADTYR is input as zero, HERSPP sets it to the data year (AADTYR) plus 20.

If the concave geometric growth rate AADTGR is greater than the maximum growth rate MAXGRW, HERSPP sets AADTGR to MAXGRW. It then sets FADTYR to AADTYR plus 20 and calculates a new value for FAADT using MAXGRW. HERSPP then re-calculates AAGRSL using the revised FAADT. (See paragraph for further details.) Geometric Values

HERSPP calculates four values for each section for later use by the HERS rural two-lane crash procedure: average curvature, average grade, and curve and grade factors.

HERSPP uses the following algorithm to compute both the average degree of curvature and the average grade of each section:

AVG equals sum from c equals 1 (LEN sub c times TYP sub c)  divided SLEN


AVG = Average degrees of curvature or average grade;
LENc = Length of section within each curve/grade class "c"
TYPc = "Typical" curvature or grade for each curve/grade class "c" (see Tables 3-12 and 3-13);
SLEN = Section length;

and the summation includes all six curve/grade classes.

To compute the curve factor, HERSPP employs the following algorithm:

CFAC equals the sum from c equals 1 to ? of LEN sub c divided by quantity SLAN time exp (0.045 time TYP sub c)

where CFAC is the curve factor, and the other terms are as in Equation 3.16.

Similarly, HERSPP computes the grade factor:

GFAC equals the sum from c equals 1 to ? of LEN sub c divided by quantity SLEN time exp (0.11 times TYP sub c)

where GFAC is the grade factor, and the other terms are as in Equation 3.16.

Table 3-12. Curve Class Associated Values
Curve Class Minimum Degree of Curvature Maximum Degree of Curvature "Typical" Values Used in Equation 3.16 Design Speed
A 0.0 3.4 0.4 70
B 3.5 5.4 4.6 60
C 5.5 8.4 6.3 50
E 14.0 27.9 18.9 30
F 28.0 -- 33.0 25
Table 3-13. Grade Classes
Grade Class Minimum Gradient (Percent) Maximum Gradient (Percent) "Typical" Values Used in Equation 3.16
A 0.0 0.4 0.2
B 0.5 2.4 1.45
C 2.5 4.4 3.45
D 4.5 6.4 5.45
E 6.5 8.4 7.45
F 8.5 -- 10.0 Horizontal and Vertical Alignment Adequacy

HERSPP can calculate the vertical and horizontal adequacy for certain sections. These sections are:

  • Rural sections with curves or grades reported, and
  • Urban principal arterials with curve data reported.

The user indicates, via AASWITCH in control file PPSPEC.DAT, whether the values for alignment adequacy coded in the section input record should be used whenever they are supplied, or if HERSPP should recalculate the adequacy values when the curve/grade information is reported.

HERS uses the procedure from the HPMS submittal software.10 Peak Percent Trucks

HERSPP sums the peak percent single unit trucks (PCPKSU, Item 81) and peak percent combination trucks (PCPKCM, Item 83) to derive the percentage of total truck travel during the peak period. Urban Freeways

HERSPP determines whether each urban section is an "urban freeway by design" and/or a "substandard urban freeway." (An urban section could be either, both, or neither.) The designations are for later use by HERS in evaluating the section. To be considered an urban freeway by design, a section must meet the following criteria:

10. YO And I'd prefer to refer the reader there, rather than include an exhaustive review of the 300+ line procedure here.

  • the section must be urban;
  • it must have at least four through lanes;
  • it must have either full or partial access control; and
  • the median must be either a positive barrier or have a width of at least four feet.

To be designated a substandard urban freeway, a section must be in functional class 11 (urban interstate) or 12 (urban other freeways and expressways) and at least one of the following conditions must apply:

  • the shoulders are not surfaced;
  • access is not fully controlled;
  • median type is not positive barrier; or
  • median width is less than the design standard. Geometrics Following Alignment Improvement

For certain sections, HERSPP calculates new values for parameters which would be affected by an alignment improvement on the section. Eligible sections are rural sections and urban principal arterials, where either or both curves or grades are reported. On sections where curve data is coded, the affected parameters are:

  • length of corrected curves after re-alignment (LAFTH);
  • average degrees of curvature; and
  • curve factor for safety calculations (see Equation 3.17).

On sections where grade data is included, the affected parameters are:

  • length of corrected grades after re-alignment (LAFTV);
  • average gradient; and
  • grade factor for safety calculations (see Equation 3.18).

The PreProcessor also recalculates the section's weighted design speed after alignment improvement. Wet

The PreProcessor examines the General Climate Zone input (item number 52) and sets the WET variable accordingly. The variable is set to one for the three wet climate codes (zones one through three), or to zero for the intermediate or dry codes. Parameters for Delay Calculations

HERSPP sets up several parameters for later use in the calculation of delay due to congestion and traffic control devices. These parameters include:

  • the section's classification into one of six delay categories (see Table 5-15);
  • a flag indicating whether the section contains both stop signs and traffic signals;

and for sections with either or both traffic signals and stop signs:

  • the average number of traffic control devices per mile;
  • the average distance between traffic control devices;
  • the ratio of stop signs to all traffic control devices; and
  • the ratio of traffic signals to all traffic control devices.
3.3.4 Conversions

HERS accepts some data items in a form or format that is different from what the model uses internally, and these items are converted by the HERSPP. Percentage Conversions

Several of the section input fields are entered as integers representing percent, that is, "70" is entered meaning 70 percent. HERSPP divides these fields by 100, expressing the percent as a fraction of one. This transforms the 70 percent example to an internal representation of 0.70. HERSPP performs this conversion for the following fields:

  • Peak percent single unit trucks - PKPCTTRKSU (Item 81)
  • Average daily percent single unit trucks - PCAVSU (Item 82)
  • Peak percent combination trucks - PKPCTTRKCM (Item 83)
  • Average daily percent combination trucks - PCAVCM (Item 84)
  • K-factor - KFAC (Item 85)
  • Directional factor - DFAC (Item 86)
  • Typical peak percent green time - PCTGRN (Item 91) County Code Conversion

When the section's state code indicates that the section is in Alaska, the section's county code is multiplied by 10. Shoulder Type Code Conversion.

HERS and the HPMS use differing codes to describe shoulder types: the HPMS recognizes six shoulder types, while HERS only processes four. HERSPP converts the HPMS codes into internal HERS codes as shown in Table 3-14.

Table 3-14. HERS Shoulder Condition Codes
HPMS Code HERS Code Description
1 3 None: no shoulders or curbs exist.
2 1 Surfaced shoulder (bituminous concrete or Portland cement concrete surface).
3 1 Stabilized shoulder (stabilized gravel or other granular material with or without admixture).
4 2 Combination shoulder (shoulder width has two or more surface types; for instance, part is surfaced and part is earth).
5 3 Earthen shoulder.
6 4 Barrier curb exists; no shoulders in front of curb. Surface Type Code Conversion

HERS and the HPMS also use differing codes to describe a section's surface. While the HERS codes identify five of the six surfaces coded in the HPMS record, HERS sets the logical variable COMPOS to true to indicate when a section with a high flexible surface type consists of a flexible overlay on a previously existing rigid surface. HERSPP converts the Surface/Pavement Type codes as shown in Table 3-15.

Table 3-15. HERS Surface Type Codes
HPMS Code HERS Code Description
1 5 Unpaved.
2 4 Low type.
3 3 Intermediate type.
4 1 High type flexible.
5 2 High type rigid.
6 1 (COMPOS flag set to true) High type composite. Metric to English Conversion

Internally, the HERS model utilizes English units of measure. Conversion from metric to English units is performed by the PreProcessor and is conditioned upon each section's UNITS field. Table 3-16 lists the conversions performed by HERSPP.

Table 3-16. Metric Conversions
Metric Unit English Unit Conversion Fields
Item Description
kilometer mile mile = km/1.609344 30 Section length
63 - 68 Curve class lengths
72 - 77 Grade class lengths
79 Weighted design speed
80 Speed limit
Meter (xx.x) Foot feet = meter/0.3048 57 Median width
59 Right Shoulder Width
60 Left Shoulder Width
Millimeters Inches inches = millimeters/25.4 51 SN or D
Meters per Kilometer Inches per Mile inches = meters × 63.36 35 IRI

There are three special cases in which HERSPP uses a "hard" conversion. The first case applies to speed limit and weighted design speed. When the input speed (in kilometers-per-hour) is a multiple of 5 between 10 and 120, HERSPP looks up the corresponding miles-per-hour speed as shown in Table 3-17. If the input speed is less than 10 or more than 120 kph, or is not a multiple of 5, HERSPP performs the conversion shown in Table 3-16.

In the second special case, HERSPP uses the hard conversion of meters to feet shown in Table 3-18 for shoulder widths through 3.8 meters; for wider widths, it uses the conversion in Table 3-16.

Finally, HERSPP uses the hard conversion values shown in Table 3-19 to convert lane widths from meters to feet. The minimum lane width is six feet, and the maximum allowed lane width is eighteen feet.

Table 3-17. Hard Conversion for Speed: Kph to Mph
Kilometers per hour Miles per hour
10 5
15 10
20 10
25 15
30 20
35 20
40 25
45 30
50 30
55 35
60 35
65 40
70 45
75 45
80 50
85 55
90 55
95 60
100 60
105 65
110 70
115 70
120 75
Table 3-18. Hard Conversion for Shoulder Width: Meters to Feet
Meters Feet
0.1 1
0.2 1
0.3 1
0.4 1
0.5 2
0.6 2
0.7 2
0.8 3
0.9 3
1.0 3
1.1 4
1.2 4
1.3 4
1.4 5
1.5 5
1.6 5
1.7 6
1.8 6
1.9 6
2.0 7
2.1 7
2.2 7
2.3 8
2.4 8
2.5 8
2.6 9
2.7 9
2.8 9
2.9 10
3.0 10
3.1 10
3.2 10
3.3 11
3.4 11
3.5 11
3.6 12
3.7 12
3.8 12
Table 3-19. Hard Conversion for Lane Width: Meters to Feet
Meters Feet
less than 1.7 6
2.0 7
2.3 8
2.4 8
2.5 8
2.6 9
2.7 9
2.8 9
2.9 10
3.0 10
3.1 10
3.2 10
3.3 11
3.4 11
3.5 11
3.6 12
3.7 12
3.8 12
3.9 13
4.0 13
4.1 13
4.2 14
4.3 14
4.4 14
4.5 15
4.6 15
4.6 15
4.8 16
4.9 16
5.0 16
5.1 17
5.2 17
5.3 17
5.4 18
5.5 18
5.6 18
5.7 or greater 18 IRI to PSR Conversion

HERS' internal calculations use PSR to represent pavement condition when evaluating deficiencies, determining speed, calculating vehicle operating costs, estimating agency maintenance costs, and forecasting pavement deterioration.

Table 3-20 presents descriptions of pavement characteristics corresponding to the various PSR levels. The exhibit also displays the IRI values (for rigid pavement) for the integer PSR values from one through five. The lowest value shown for PSR (0.068) was chosen to correspond to an IRI of 999.

Section input records might contain either, both, or neither PSR or IRI values. The HERSPP control file, PPSPEC.DAT, contains a flag to give the user control over selecting PSR or IRI for sections which contain both entries. Table 3-21 displays the logic used by HERSPP in determining the source of the PSR value which is passed to the HERS program. HERSPP selects one of three equations for the IRI to PSR conversion based upon the section's surface type. Table 3-22 displays the three equations.

3.3.5 Processing the User-Specified Improvements File

HERSPP reads the PPSPEC.DAT text file for the following three items which control the processing of user-specified improvements:

  • the Override Flag;
  • the name of the text file containing the user-specified improvement information; and
  • the name of the binary file to contain the processed user-specified improvement information.
Table 3-20. Pavement Condition Ratingsa
PSR and Verbal Rating IRI Value (Rigid)b Description
a. Source: U.S. Department of Transportation, Federal Highway Administration, Highway Performance Monitoring System Field Manual, Washington, D.C., December 1987, p.IV-28. The version in the April 1994 edition excludes the verbal ratings.

b. Rounded to whole inches per mile.
5.0 0
Very Good Only new (or nearly new) pavements are likely to be smooth enough and sufficiently free of cracks and patches to qualify for this category. All pavements constructed or resurfaced during the data year would normally be rated very good.
4.0 52
Good Pavements in this category; although not quite as smooth as those described above, give a first class ride and exhibit few, if any visible signs of surface deterioration. Flexible pavements may be beginning to show evidence of rutting and fine random cracks. Rigid pavements may be beginning to show evidence of slight surface deterioration, such as minor cracks and spalling.
3.0 119
Fair The riding qualities of pavements in this category are noticeably inferior to those of new pavements and may be barely tolerable for high speed traffic. Surface defects of flexible pavements may include rutting, map cracking, and extensive patching. Rigid pavements in this group may have a few joint failures, faulting and cracking, and some pumping.
2.0 213
Poor Pavements that have deteriorated to such an extent that they affect the speed of free-flow traffic. Flexible pavement may have large potholes and deep cracks. Distress includes raveling, cracking, rutting, and occurs over 50 percent or more of the surface. Rigid pavement distress includes joint spalling, faulting, patching, cracking, scaling, and may include pumping and faulting.
1.0 374
Very Poor Pavements that are in an extremely deteriorated condition. The facility is passable only at reduced speeds and with considerable ride discomfort. Large potholes and deep cracks exist. Distress occurs over 75 percent or more of the surface.
0.068 999

If the Override Flag is set to zero, HERSPP deletes any existing copy of the specified binary file. Otherwise, HERSPP processes the text file and creates a new copy of the binary file.

Table 3-21. Derivation of Initial PSR Value
Input record Contains User Flag Specifies Source of Initial PSR
Both PSR and IRI PSR Input PSR
Both PSR and IRI IRI HERSPP converts input IRI to PSR
PSR only n/a Input PSR
IRI only n/a HERSPP converts input IRI to PSR
Paved section, neither PSR nor IRI reported n/a Default PSR value of 3.2
Unpaved section n/a User-specified default PSR for unpaved sections
Table 3-22. IRI to PSR Conversion Equations
Surface Type Equation
Flexible PSR = 5.0 × exp(0.0038 × IRI)
Composite PSR = 5.0 × exp(0.0046 × IRI)
Rigid PSR = 5.0 × exp(0.0043 × IRI)

HERSPP first validates that the number of improvements specified (EI_COUNT) is within range. If not, it sets the flag VALID to false.

HERSPP then checks for invalid conditions when setting the override code to zero or the improvement year to zero, as shown in Table 3-23.

Table 3-23. Error Conditions for User-Specified Improvement Input
Year Improvement Type OverRide
non-zero 0 0 err msg: bad prevent, discard imp
0 discard improvement
0 0 discard improvement

HERSPP examines the user-specified improvement code. If the code indicates adding lanes, it checks the EI_LANES code. If it is equal to zero, it sets EI_LANES to 1 and issues a warning message.

If the sum of existing lanes and added lanes is odd, and the section is two-way, and the user has not specified the new capacity, HERSPP makes the final number of lanes even. (This is because the capacity routines do not have the capability to figure capacity for odd-laned two-way facilities.) If the number of lanes being added is odd, the number is increased by one; if even, it is decreased by one. HERSPP issues a warning message.

If the improvement does not add lanes, then HERSPP sets the number of lanes being added to zero and issues a warning msg. (The improvement type overrides the number of lanes entry.)

If the user has specified a combination improvement (HERS type + non-HERS type), HERSPP checks the override flag. If it is not set to one, HERSPP forces it to one and issues a warning message.

The model next has code to handle the case of an override code equal to zero and an improvement type set to zero, in which it would set the override code to one. This code assumes that the user wanted to specify that the section would be unimproved during the funding period. However, previous code would have discarded this improvement. This code is therefore never exercised. <<YO-- need to ask David/Herb/Nate.

If the specified improvement is a pure non-HERS type (that is, not in combination w/ a HERS type imp) and the user has not specified a cost for the imp, HERSPP assigns a cost of $1.00.

If the improvement is a combination of HERS-type and non-HERS-type, and no cost has been specified, HERSPP sets the cost to $2.00. The code is annotated: HERS will later recognize the $2 as a special value indicating it should use the cost of the HERStype improvement as the total cost of the improvement.

HERSPP next sets EI_YEAR(J) to the year, relative to the baseyear (which is now read per record, rather than from the distribution file), in which the improvement is to be implemented. The algorithm, although noting a possible 2070 problem, actually doesn't work for base years before 1970.

HERSPP finally writes the binary output record for the section. Table 3-24 displays the output record format. As with the input record, the first three fields identify the section, and the remaining fields define improvements. Unlike the input format, where the minimum number of fields are used to define the desired improvements, the binary record contains a set of arrays. The arrays provide sufficient elements for the maximum number of definable improvements. HERSPP does not indicate the meaning of the Used flag, and the final scalar flag is not named.

Table 3-24. User-Specified Improvement Output File Fields
Field Item Format
1. Number of Improvements scalar integer
2. County Code scalar integer
3. Sample Identifier scalar alphanumeric
4. Year of Improvement array integer
5. Relative Year of Improvement array integer
6. Type of Improvement array integer
7. Type of HERS improvement array 1-19 integer
8. Type of Non-HERS Improvement array 0,20,40,60, or 80 integer
9. Override Flag array integer
10. Cost of Improvement array floating point
11. Lanes To Add array integer
12. Increase in Capacity array integer
13. "Used" Flag array .false logical
14. Another Flag scalar .false logical
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Updated: 06/27/2017
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