Attachment 3

SPEED METHODOLOGY MEMO FROM NYSDOT
SPEED ESTIMATES FOR USE IN

1994 AIR QUALITY STATE IMPLEMENTATION PLAN

October 24, 1994

by GUNNAR HALL, Associate Transportation Analyst

PLANNING DIVISION

NEW YORK STATE DEPARTMENT OF TRANSPORTATION
CONTENTS

 1. Overview 2

 2. Data Collected in 1994 5

 3. Time Periods 5

 4. Speed-Travel Volume

relationships 6

 5. Notes on Speed Calculations 7 

 6. Actual Computations 10

 7. Worksheet Orientation 10

 8. Results 12 (T1..T12)

 Attachments

1. OVERVIEW 

This report documents the procedures, data sources and estimated highway speeds for 

1990 through 2007, needed for this year's update of the Air Quality State Implementation 

Plan. A Lotus worksheet was prepared to carry out the necessary calculations. The 

average highway speeds for 1990, 1996, 1999, 2002, 2005 and 2007 for selected urban areas 

and the rest of the State are presented at the end of the report. 

The NYS Department of Environmental Conservation requested the speeds for six urban 

and six rural functional classes, in four time periods (morning, day, evening and night) for 

each geographic area. 

Speeds have changed from last year's submission for four major reasons: 1) The requested 

time periods - morning, day, evening and night - are different from those used last year -

prime time and off-prime for the New York Metropolitan area; peak, off-peak, midday 

and midnight for upstate areas. 2) 12 functional classes are used, versus 6 functional class 

groups last year. 3) Additional speed and VMT data was obtained from urban areas with a 

functioning urban transportation model, and finally 4) The speed estimation procedure is 
more directly tied to procedures recommended in the current Highway Capacity Manual, 

while consistency with last year's results have been attempted.

Speeds are determined for each time period through a number of successive steps that will 

be described in detail below. A general outline of the procedure is shown in Table 1. It 

may be useful for quick reference when the details have become familiar. 

TABLE 1: SUMMARY REVIEW OF SPEED ESTIMATION PROCEDURE

 1 Speed data for a base and a future year is collected from Metropolitan Planning 

Organizations (MPOs) that maintain urban transportation network analysis 

models. Upstate MPOs provide peak hour and off-peak hour speeds for all 

functional classes; the NYMTC provides 24 hour average speeds for three 

functional class groups for the New York metropolitan area (NYA). 

 2 Speeds for intermediate years are linearly interpolated between the base and 

future years.

 3 The relationship between speed and the volume -capacity ratio (vcr) for different 

functional classes are identified from the 1985 Highway-Capacity Manual (HCM) 

and other sources. While these relationships are given in different forms, and 

converted to equations in the final speed calculation worksheet, they are referred 

to here as the HCM speed-vcr curves.

 4 Speeds are described as initial, preliminary and final speeds. Initial speeds are 

read or computed directly from the HCM speed-vcr curves. Preliminary speeds 

are generally proportional to the initial speeds obtained from the HCM speed 

curves. The final speeds are based on adjustments of the preliminary speeds to 

reflect differences between MPO model and HCM based off-peak speed data. 

Final speeds are the speeds presented in the worksheet.

 5 The peak hour vcr for freeways and expressways in upstate areas is estimated 

from the peak hour speed and HCM curves. The HCM speed-vcr curves were 

designed for individual facilities rather than for systems (functional classes) with a 

variety of different facilities. However, interstates and freeways are designed to 

similar standards everywhere and therefore, the freeway speed-vcr curves should 

closely match actual speeds. 

 6 The peak hour vcr for upstate urban and rural freeways provide reference points 

from which the vcr and corresponding speeds for each time period is determined. 

For urban arterial, collector and local systems, the volume capacity ratio at peak 

periods have been assumed to be the same as the freeway vcr. In rural areas these 

speed-vcr relationships are linear and speeds can be determined directly from the 
peak and off-peak data supplied by the MPOs. 

 7 In the NYA, traffic during the evening period is assumed to equal capacity for all 

functional class systems except for freeways in Suffolk, Westchester, & Rockland 

where the evening peak vcr is assumed equal .9 and in Putnam where .8 is 

assumed. Evening speed is then read from the HCM curves.

 8 The vcr for a requested time period is related to peak hour or peak period vcr 

through the known temporal distribution of VMT. With vcr calculated, the 

speed-vcr curve allows the calculation of initial speeds.

 9 In the NYA and for upstate arterial and local systems, preliminary speeds are 

assumed to be proportional to, but not the same as the initial speeds obtained 

directly from the HCM speed-vcr relationships.

10 In the NYA, preliminary speeds are computed as functions of the 24 hour average 

speeds obtained from the NYMTC model, the initial time period speeds read from 

the HCM speed-vcr curve and the computed 24 hour average speeds based on 

these initial period speeds. 

11 Upstate, the preliminary speeds are calculated as a function of the peak period 

speed obtained from the MPO models, the initial time period speeds and the initial 

peak period speed computed from the HCM speed-vcr curves.

12 In the NYA, the 24 hour average speeds in each county were available for only 

three functional classes. To estimate speeds by the required 6 functional classes, 

the distribution of VMT between functional classes were obtained from HPMS 

data. A speed difference between the two functional classes represented in each 

functional class group was assumed: The average speed in the lower functional 

class was assumed to be 95% of the average speed in the higher functional class. 

13 To calculate the 24 hour average speeds from HCM, a selected vmt is divided by 

the total travel time for that vmt for all time periods, in both functional classes 

included in a functional class group.

14 Adjustments to preliminary upstate speeds are made to insure that estimated offpeak speeds are consistent with off-peak speed data submitted by the MPOs. The 

off-peak vcr was determined from the assumptions made by the MPOs for 

computing these speeds. Initial and preliminary off-peak speeds were then 

estimated based on the HCM speed-vcr curves. 

15 The adjustment factor is applied to the difference between the peak period speed 

and the preliminary spe ed calculated for any given time period. At the peak hour, 

no adjustment is needed, since at this point the HCM initial speed is the reported 

or assumed speed. 
2. DATA COLLECTED IN 1994

Estimates of highway speeds by 6 urban and 6 rural functional classes were requested from 

New York's Metropolitan Planning Organizations (MPOs) on February 17 (Attachment 2). 

These organizations maintain urban transportation network analysis models designed to 

estimate such speeds for the facilities included in their coded network. These networks 

include arterial and freeway facilities and most major collectors but do not include a 

representative sample of minor collectors or local roads. 

Upstate MPOs provide peak hour and off-peak hour speeds for all functional classes 

represented; the NYMTC provides 24 hour average speeds for three groups of two 

functional classes each in the New York metropolitan area (NYA). For functional classes 

not adequately represented in their analysis models, some MPOs provided speed estimates, 

others did not. The speed estimates received was examined and generally accepted. 

Default values estimated based on speed data provided in other areas were used in a few 

cases when speeds were omitted or apparently unreasonable, as follows:

system peak hour 

speed

off-peak speed

CDTC, urb, local

 rur, local 

25

25

NFTS, rur, maj. collectors

 min. collectors

 local

40

35

30

45

40

35

BMTS last year's data last year's data

Speeds for the 1990 base year were provided by all MPOs; future year speeds were 

generally for the year of their "planning horizon" (2010 or 2015). The differences in 

present and future speeds were generally small and the selected linear interpolation of 

given speeds for the necessary forecast years should give reasonable results. 

 
3. TIME PERIODS

The specific hours of the day included in each time period were suggested by DEC, as 

indicated in Attachment 1: Time of Day Factors used to Estimate Hourly VMT. The 

temporal distri-bution of travel by hour of the day shown in this attachment for the New 

York metropolitan area was developed by NYMTC and reflect survey results of the 

Nationwide Personal Transportation Study. The distribution shown for upstate urban and 

upstate rural areas was supplied by DOT Data Services Bureau. These data items are 

described in a memo from Cohen to Cioffi, dated 5/26/92.

Table 1 summarizes this data by the four requested time periods and for the peak hour:

TABLE 2: PERCENT OF VMT PER DAY

Time Period No of

Hours

N.Y. Metro

Area

No of

Hour

s

Upstate 

Urban

Upstate

Rural

Morning 5 23.0% 4 17.0% 21.7%

Day 4 21.0% 6 36.7% 30.2%

Evening 5 40.6% 3 23.4% 25.0%

Night 10 15.3% 11 23.9% 23.1%

Peak hour vmt 1 8.8% 1 8.2% 8.9%

4. SPEED - TRAVEL VOLUME RELATIONSHIPS

The relationship between speed and the volume -capacity ratio (vcr) for the facility types 

typical of each functional class was identified from the 1985 Highway-Capacity Manual 

(HCM) and other sources. These relationships are given in different forms, and converted 

to equations in the final speed calculation worksheet. Seven facility types were used: 

 for freeways and expressways in the New York Metro area;

B. Freeways with 70mph design speed, 4 lanes (HCM, figure 3-4),

for upstate urban and rural freeways, urban expressways and

rural principal arterials;
C. Urban arterials with 10 signals per mile (HCM, table 11-9),

for principal and minor arterials in Manhatten;

D. Urban arterials with 5 signals per mile (HCM, table 11-8),

for arterials in urban areas other than Manhatten, and

for collectors and local streets in the New York Metro area;

E. Rural arterials with 55mph max speed (HCM 1965, figure 10-1),

for rural minor arterials and major collectors;

F. Urban streets (HCM 1965, figure 10-3),

for urban collectors and local streets outside NYA;

G. Local roads with 45mph max speed (HCM 1965, figure 10-1), 

for rural minor collectors and local roads. 

As noted, some of these relationships are given by tables and some are given graphically. 

Each of these were converted into one or two algebraic equations for use in the worksheet 

as follows:

TABLE 3: SPEED-VCR RELATIONSHIPS

A prelim. spd read directly from HCM figure 3-4 (since NYA vcr is 

assumed)

B spd = 30 + (50000*(1-vcr))^.333 for .80 < vcr <= 1 

spd = 60 - 1.46*vcr - 11.46*vcr^2 for 0 < vcr < .80

C prelim. spd read directly from HCM table 11-9 (since NYA ref.vcr=1)

D spd = 12.8 + 21*(1-vcr)^.65 for .74 < vcr <= 1

spd = 12.8 + 12*(1-vcr)^.30 for 0 < vcr < .75

E spd = 55 - 25*vcr

F spd = 15 + 24.4*(1-vcr)^.48 for .65 < vcr <= 1

spd = 17 + 15*(1-vcr)^.14 for 0 < vcr < .65

NYA prelim. spd read directly from HCM(65) fig 10-1 (since ref.vcr=1) 

G spd = 45 - 25*vcr

5. NOTES ON SPEED CALCULATIONS

With speeds the basic input data source, a reference point in the speed-vcr curve is needed 

in order to use them to determine the average speeds in the desired time periods. In 

upstate urban and rural areas, the urban transportation models determined the peak hour 
speed for each functional class (speeds in the "rest of the State" are assumed to equal 

speeds in the Binghamton urban area). With this speed, the corresponding vcr is 

determined, using the assumed relationships. 

In the New York metropolitan area, the NYMTC highway evaluation model (HEM) 

determine the 24 hour average speed, which can not be related to a point on the speed-vcr 

curves. However, in this area we know that most of the highway system operates near 

capacity levels in the evening peak period. For freeways and expressways within the city, a 

peak period volume capacity ratio of 1 is assumed. In Suffolk, Westchester and Rockland 

counties, vcr=.9 was assumed and in Putnam county, vcr=.8. This deviation from a general 

vcr = 1 was needed to assure consistent reasonable speeds in other time periods. For other 

systems in the New York metropolitan area, the volume capacity ratio of 1 is assumed 

since this will only impact differences in speed between time periods but not their average 

value. With the vcr assumed we have a reference point on the speed-vcr curve.

The Volume Capacity Ratio for a requested time period is related to peak vcr through the 

known temporal distribution of VMT. From the data given in Table 1 above, the VMT per 

hour is calculated for any system, with an assumed total VMT of 100,000 per day. Since 

the physical capacity of the system is the same in all time periods, the vcr for a requested 

time period equals the vcr computed or known for the peak period multiplied by the ratio 

of hourly volumes in the given time period and the peak period.

From the vcr for a given time period, an initial or preliminary average speed for that 

period is computed from the formulas shown in Table 2 above. In the NYA and for upstate 

arterial and local systems, where preliminary speeds are assumed to be proportional to, but 

not the same as the speeds obtained from the HCM speed-vcr relationships, preliminary 

speeds are computed from the following relationship:

 upstate: 

SPEED(period) = SPEED(peak) * SPEED(period,HCM) / SPEED(peak,HCM) 

 in the NYA:

SPEED(period) = SPEED(24hr ave) * SPEED(period,HCM) / SPEED(24hr ave, 

HCM)

 where

SPEED(period) = preliminary speed computed for a given time period.

SPEED(period,HCM) = initial speed for the time period from the 

HCM curves.

SPEED(peak) = known peak hour speed obtained from urban models.

SPEED(peak,HCM) = initial peak speed estimated from the HCM curves,
using the peak vcr estimated for freeways.

SPEED(24hr ave) = 24 hour average speed in the NYA, from NYMTC.

SPEED(24hr ave,HCM) = initial 24 hour average speed from HCM 

relationships, estimated by dividing a selected daily level 

of VMT by the corresponding number of hours travelled, at the 

initial speeds in all time periods.

To calculate the 24 hour average speeds from HCM, a selected vmt is divided by the total 

travel time for that vmt for all time periods, in both functional classes included in a 

functional class group.

The numerator and denominator in the formula for the period speed of a given system may 

use different formulas from Table 2 when the vcr for the peak and the desired time period 

straddle the validity range limit. Thus, the formulas used to calculate, say evening speeds 

for upstate urban arterials, may not be the same for all upstate urban areas. 

In the NYA, the 24 hour average speeds in each county were available for only three 

functional classes. To estimate speeds by the required 6 functional classes, the distribution 

of VMT between functional classes were obtained from HPMS data and a speed difference 

between the two functional classes represented in each functional class group was made : 

The average speed in the lower functional class was assumed to be 95% of the average 

speed in the higher functional class. 

Adjustments to preliminary speeds are made to insure that estimated off-peak speeds are 

consistent with off-peak speed data submitted by the MPOs. First, the volume capacity 

ratios corresponding to the off-peak speeds were determined. The MPOs defined off-peak 

speeds in different ways and therefore, the vcr for off-peak speeds varied by geographic 

area. The Capital District and Rochester urban area transportation systems were modeled 

using 38% of peak hour trips to obtain off-peak speeds. Thus off-peak vcr was assumed to 

be 38% of peak hour vcr. Syracuse used 50% of peak hour trips to obtain off-peak speeds. 

Buffalo determined off-peak speeds based on free-flow conditions, so for this area the offpeak vcr was assumed equal to zero. 

Given the off-peak vcr, an off-peak speed based on the HCM speed-vcr curve is easily 

determined. At this vcr, the final adjustment is simply this HCM speed estimate less the 

MPO based off-peak speed. For other time periods the adjustment depend on the 

difference in estimated time period speed and the peak hour speed. 

The preliminary speeds for the four desired time periods are adjusted using a speed 

multiplication factor. This factor is the difference between the off-peak speed as calculated 

from the HCM curves at the off-peak vcr and the assumed correct off-peak speed reported 

by the MPOs, divided by the difference in estimated off-peak and peak hour speeds, 
multiplied by the difference in estimated preliminary time period speed and the peak hour 

speed. At the peak hour, the adjustment is zero; for the off-peak vcr, the adjustment is as 

calculated above.

6. ACTUAL COMPUTATIONS

Attachment 3 illustrates how the computations discussed above are carried out in the 

worksheet. 

Pages 3a through 3d show a section of the worksheet with all formulas used for the 

calculation of night, morning, day and evening speeds for urban functional classes in the 

Capital District. All data elements used in these calculations are shown and referenced to 

their location. 

Pages 3e through 3g similarly show a section from the New York Metropolitan Area. The 

data given above row 141 and to the right of column R is not shown in the final printout of 

results. As noted above, the procedure and formulas used are different from those used in 

upstate urban areas.

7. WORKSHEET ORIENTATION

A. Final Results and Printouts:

a16....r65 Upstate urban areas of Capital District, Syracuse and

Rochester

a66...r112 Upstate urban areas of Buffalo and Binghamton

a153..q207 New York Metropolitan Area; Manhatten, Bronx, Kings, Queens,

Richmond, Nassau, Suffolk 

a208..q232 New York Metropolitan Area; Westchester, Rockland, Putnam.

a233..r248 Rest of State.
B. Data Required for Worksheet Operation

a8.....r15 Upstate VMT and Time Period data

s17...w112 Upstate Peak and Off-Peak Speeds, 1990 and horizon year;

adjustment factors.

x16...y112 Upstate Off-peak adjustments DMAX; estimate years.

a116..l151 Downstate VMT and Initial Speed data

s153..v230 Downstate 24 hour speeds, 1990, 1996, 2005, 2015.

w153.aa230 Downstate hours travelled, by time period and total.

aa97..ae112 Peak and Off-Peak Speeds and VMT data for Binghamton

C. Speed Calculation Factors and Formulas (not printed)

a254..k342 Upstate general data, Freeways and Expressways, Arterials,

Local Roads and Streets

a346..l364 Downstate general data, Freeways and Expressways, Arterials,

Local Roads and Streets

D. Miscellaneous (not printed)

b1......c8 Print Macros \p, \r, \i, \n

e1......r6 Formulas used

z1....aw21 Formula development
8. RESULTS

1990, 1996 Capital District, Syracuse, Rochester T1

Buffalo, Binghamton T2

NYA: New York City; Nassau, Suffolk T3

NYA: Westchester, Rockland, Putnam, 

Rest of State T4

1999, 2002 Capital District, Syracuse, Rochester T5

Buffalo, Binghamton T6

NYA: New York City; Nassau, Suffolk T7

NYA: Westchester, Rockland, Putnam, 

Rest of State T8

2005, 2007 Capital District, Syracuse, Rochester T9

Buffalo, Binghamton T10

NYA: New York City; Nassau, Suffolk T11

NYA: Westchester, Rockland, Putnam, 

Rest of State T12
TO:

FROM:

SUBJECT:

DATE:

J. Ralston, NYSDEC

G. J. Cioffi, Urban Planning Section, 4-206

SPEED ESTIMATES FOR AIR QUALITY

STATE IMPLEMENTATION PLAN

November 4, 1994

Attached for your use are average highway travel speeds for 1990, 1996, 1999, 2002, 

2005 and 2007; they are presented in the attached report "Speed Estimates for use 

in 1994 Air Quality State Implementation Plan". The speed data was developed

using the functional classes, geographic breakdown and time periods requested

(four time periods; 12 functional classes; selected urban areas and rest of State).

A draft of this report, dated June 15, was sent to you on August 26 by Mike Fay. 

The major changes from the draft are described on a separate, attached sheet. The 

new grouping of VMT by morning, day, evening and night in the New York

Metropolitan area resulted in significant changes in the corresponding speeds. 

Other changes had minor impacts, but were included to improve the general quality 

of the report. 

The report documents the procedures and data sources used to calculate these

speeds. A Lotus worksheet named 94SPEEDS.WK3 was prepared to carry out the 

necessary calculations. It shows precisely how the speed data was developed and is 

included to clarify any procedures that may have been inadequately described in the 

attached documentation. We hope that it addresses the relevant issues regarding 

speeds for the SIP analysis. If you have further concerns, please call. 

Attachments

cc: R. Tweedie, Data Services Bureau, 4-115 

J. Zamurs, Envir. Analysis Bureau, 5-303 

N. Erlbaum, Data Services Bur., 4-115 

G. Hall, Urban Planning Section, 4-207 
TO REVIEWERS OF JUNE 15 DRAFT:

The major changes from the previous draft of this report are as follows:

1. The temporal distribution of VMT in the New York Metropolitan Area and the grouping of 

VMT by morning, day, evening and night has changed. This affected all speed estimates 

for all counties in the New York area. The revised temporal distribution is summarized in 

Table 2 on page 6 and included in Attachment 1. 

2. Page 4, first paragraph and Page 8, first paragraph: With the evening peak period now 5 

hours, it has been assumed that freeways and expressways in Suffolk, Westchester and 

Rockland counties have an average vcr = .9 during the evening peak and in Putnam county, 

vcr = .8. This deviation from the previously used assumption of vcr = 1 for all systems in 

the metropolitan area was needed to assure consistent and reasonable speeds in non-peak 

time periods. For other systems, the assumed vcr = 1 is retained since the assumed volume 

capacity ratios will only impact differences in speed between time periods and not their 

average level.

3. The speed - volume relationship for arterials in the New York Metropolitan area counties 

outside Manhattan has been changed to follow Table 11-8 (Table 11-9 was used before) of 

the highway capacity manual. Table 11-8 is also used for urban collectors and streets in 

these counties. This is stated on page 6, section 4 C & D and reflected in the tables of 

section 12. 

These changes result in final speed estimates that more closely conform with earlier

estimates by NYMTC.

4. An attempted clarification of Table 1, section 4 on page 3. A typographic correction of the 

same table, in section 12 last line to read: 95% rather than 90%.

5. Miscellaneous minor wording and cosmetic changes.