METHODOLOGY

FOR

SELECTING URBAN MEDIAN A USER'S MANUAL

Parker,

Martin

R. Research

(The

report

(A

TREATMENTS"

Jr.

Scientist

opinions, are

findings, and conclusions expressed in this those of the author and not necessarily those o the sponsoring agencies.)

Virginia Highway & Transportation Research Council Cooperative Organization Sponsored Jointly by the Virginia Department of Highways & Transportation and the University of Virginia) Charlottesville, Virginia July VHTRC

Revised

1981 82-R3

March

1982

f

TRAFFIC

Chairman,

II,

L.

C.

TAYLOR,

J.

B.

DIAMOND,

J.

E.

GALLOWAY,

C.

0.

LEIGH,

R.

F.

MCCARTY,

W.

C.

NELSON,

H.

E.

PATTERSON,

R.

L.

PERRY,

F.

D.

RESEARCH

District

JR.,

ADVISORY

Assist.

Maintenance

Engineer,

State

Engineer,

Safety Coordinator, JR.,

Assist.

Traffic

District

Traffic

COMMITTEE

Traffic

Engineer,

Transp.

ii

VDH&T

VDH&T FHWA &

Safety Engineer, Norfolk

VDH&T

Department

Planning Engineer, VDH&T SHEPARD, Highway Research Scientist, VH&TRC Assist.

VDH&T

VDH&T

Materials

Traffic Engineer, Public of Works

Senior

Engineer,

FOREWORD

This

Lser's

manual is a result and Transnortation

of a study conducted by the Research Council at the request of the Virginia Department of Highways and Transportation. The study was initiated and conducted by Martin R. Parker, Jr. Because Mr. Parker left the Research Council before the end of the project, a draft of the manual was completed by William Galbraith and Mr. Parker made the final revisions and editing necessary for publication.

Virginia Highway

The companion report, "Development of Design Guidelines for and Traversable Medians in UrbanAreas, contains a comnlete record of the research conducted.

Raised

advice

This of

project the

performed

was

Research

Task

Force

of R. R. F. D. F.

E. L. F. M. L.

Atherton, Perry Small

Wa•ner

Lovegrove

iii

under on

the Urban

Chairman

general Median

guidance and Design consisting

TABLE

FOREWORD

0F

CONTENTS

....................................................

INTRODUCTION ALTERNATIVE

iii

-

MEDIAN

TREATMENTS

Raised Medians Traversable Medians GUIDELINES FOR SELECTING Data Collection Accident Analysis

MEDIAN

TREATMENT

•6

Delay Analysis Economic Analysis Considerations Selection of Median Type

Other

EXAMPLE

APPLICATIONS Example i Example 2 Example 3

OF

THE

GUIDELINES

REFERENCE APPENDIX

i0 II Ii Ii .14 16 21

PROGRAM

MEDEQU-

METHODOLOGY

FOR

SELECTING URBAN MEDIAN A USER' S MANUAL

TREATMENTS"

by Parker,

Martin

R. Research

Jr.

Scientist

INTRODUCTION Urban for

arterial

through traffic

resenting a variety traffic service and flicting functions

streets well as

as

high level of service abutting properties repextent, the provision of

provide

must

a

to

access

of land uses. To an the accommodation of access needs are conthat require different median treatments and different access controls. The regulation of left-turn traffic through the utilization of alternate median co.ntrols is a primary method, of providing a compromise.

Although several investigators have examined the merits of raised medians and traversable or continuous two-way, left-turn median lanes, guidelines for selecting the treatment best suited for medians under particular urban conditions have not been fully developed. The absence of guidelines has led to considerable differences in opinion among planners, designers, and traffic engineers, and often the design chosen has .generated criticism from the motoring public, property owners, and businessmen. The purpose of the study renorted here was to develop guidelines that can be used to formulate a rational basis for selecting alternative median designs for nonlimited access urban highway

projects. I. 2.

The

specific objectives

examine the process median treatments;

of

the

currently

study

used

to

were

select

determine traffic operational, land use, and characteristics that are best served by median and the characteristics that raised a favor a continuous two-way, left-turn median

other lane

3.

investigate median

4.

to

the

accident

treatments;

histories

of

various

and

provide guidelines that the appropriate median

can

be

used

treatment.

to

select

The

of

art in urban median treatments was deteravailable literature and analyzing the results questionnaire sent to design engineers in major U. $.

state

of

by reviewing

mined

the

survey and state departments of transportation. sented here are based on field and accident data Virginia for a three-year period. The remainder consists ofa

cities

I.

2.

a

discussion

guidelines ments

3.

for

of

this

sites

pre-

in

manual

treatments;

selecting alternative median

example applications

median

warrants

50

treat-

and

ALTERNATIVE The

median

alternative

of

The at

treatments

of

the

MEDIAN

guidelines.

TREATMENTS

included

in the

study fall into

two

categories. The raised median prohibits crossings of the median except at openings selected •by the designer. The traversable median provides a continuous, left-turn median lane but does not physically restrict the movement of traffic across the median. The advantages and disadvantages of each of these median treatments are discussed

below.

Raised

Medians

Shown in Figures I and 2 are of the designs has a concrete combination of grass and concrete

Each

Raised

medians

by preventing turn storage streets and

pedestrians.

usually render

typical raised median treatments. curb and, for most projects, a cover. a

high degree

of

traffic

service

turns except at crossovers and providing leftleading to major intersecting at crossovers driveways. Raised medians also provide a refuge for

left lanes

minimum desirable width of a raised median is 14 feet; if there is a need to accommodate U-turning traffic or to shadow vehicles turning left from adjacent streets, a minimum width of 25 feet is necessary. Wide medians are seldom cost-effective in urban areas because of the cost.of.right-of-way. The

however,

Figure

i.

Raised

median

Figure

2.

Raised (Taken

median

A

from

with

concrete

with grass i97i edition

(i) cover.

(I) cover.

of MUTCD. )

disadvantage of raised medians where there is a large demand left turns and crossovers not provided is that required to use an indirect,are circuitous route and Uadjacent, crossovers to reach their destinations. Also,

mid-block motorists are for

turn

at

the curb road

reduces

the

recovery

area

Traversable

for

motorists

who

run

off

the

Medians

basic types of traversable medians are (I) the conleft-turn lane, (2) the alternating left-turn lane, and (3) continuous left-turn lanes. These median configurations in Figures shown 3, and 5. medians orovide a 4, Traversable are high degree of traffic service and allow direct access to adjacent property .from both directio•ns of travel. The

tinuous,

three

two-way

The continuous, two-way, left-turn median lane, shown in Figure 3, is perhaps the most widely used type of traversable

median.

The

purpose

of

the

median

lane

is

to

store

left-turn

Figure

3.

Figure

Continuous,

4.

two-way,

Ai•e•nating,

left-turn

left-turn

median

median

lane.

lane.

(I)

Yellow crosshatching in islands permissible

Figure

5.

Continuous, (Taken

from

left-turn median .lanes. 1971 edition of MUTCD.)

(I)

(I)

throhgh

vehicles without impeding traffic. The desirable width of the median lane is 12 feet and the typical maximum width is 14 feet. In cases where ll-foot lanes are being unitized for the through travel lanes, it is satisfactory to use an ll-foot median lane. A continuous, two-way, left-turn median lane can often be provided on existing right-of-way at a lower cost than a raised median. The median lane is also a flexible design that can be altered to meet changing access needs, and it can be used as an additional through lane, with appropriate markings and signalization, during peak hours. Concerns that two-way operation will promote head-on collisions do not appear to be supported by accident statistics and observations of traffic movement. use are

One major advantage of the traversable median of the median lane as a temporary through lane closed for maintenance work. A

reported disadvantage

of

the

two-way,

is the potential when travel lanes

left-turn

lane

is

that

provide appropriate channelization at major intersections. Also, it has been suggested that some drivers do not appear to understand the meaning of the pavement markings. The alternating left-turn lane shown in Figure 4 is another type of traversable median that provides storage for left-turning vehicles. In this case, left turns are permitted for only one direction at a time; thus direct access to some properties may not be permitted. Alternating left-turn lanes are best suited to areas that have well-defined and heav-ily-used access points with few driveThe desirable width of the ways between the major intersections. median lane is 12 feet. Similar to other traversable medians, the alternating left-turn lane is a flexible design that can be altered Accidents and delay to to accommodate changing access needs. through traffic caused by left-turning vehicles have been reported to be significantly decreased by this median treatment as compared to undivided highways. The continuous, left-turn median lanes, shown in Figure 5, are similar in concept to the two-way, left-turn lane shown in Figure 3, excep.tthat separate left-turn lanes are provided for each direction of travel. Painted islands are utilized at major intersections to prohibit left turns and through movements at the far side of the intersection. This treatment provides a high degree of traffic service and access needs; however, a major disadvantage is that a 24-foot median width is required. Due to the additional right-ofway required for this design and the additional construction costs, it does

this

not

treatment

usually is

not

cost-effective.

GUIDELINES

FOR

SELECTING

MEDIAN

TREATMENT

general methodology depicted in Figure

6 assists in the either a raised or traversable median treatment for four-lane, nonlimited access highways in urban areas. The six: elements shown in the figure are discussed below. In addition, the Appendix gives instructions for using a computer program to estimate accident and delay characteristics for the median treat-

The

selection

of

ments.

DAirY% COLL•.CTIo• ACCIDENT

ECONOMIC

0THE•

Figure

selection•process. Collection

Data

be

For each section collected for each

of of

ANALYSIS

CONSIDERATIONS

Median

6.

ANALYSIS

ANALYSIS

DELAY

roadway under consideration, items

the

data

must

in Table I. Where considered for separate be assembled for each

shown

different median treatments are being sections of a project, the data must section separately. These data are used to calculate the in shown 2, which are necessary for the accident Table measures and

delay analysis

economic

analysis

and when the designer of the alternatives.

Table Data

Section Number

length of

Required

for

(miles)

.traffic

signals

Average daily traffic

(ADT)

wants

i

Median

Analysis

to

conduct

an

Design hourly are

(assume

volumes

10%

of

ADT

if

no

available)

Number

of

intersecting public

section would be intersection has

counted

only

(a streets two streets,

as

other

four-way interwhereas

street)

one

data

a

T

of driveways (includes all intersections excent public streets) City or area populati.on Number of median openings (applies only to raised median) The following items are needed only when an economic Noteanalysis is conducted. Number

Cost

of

each

alternative

Average daily left-turn Table

Independent Variables Var iab i

Signals

per

median volume

treatment

(total

for

Regression Analysis Symbo

e

Design hourly volume Driveways per mile Area population

DHV

Median

i

Sig

mile

ADT

per

section)

2

Average daily traffic

Streets

for

Pop.

mile

openings Accident

per. mile

Open

Analysis

The accident analysis is used to estimate the annual number of accidents per mile-for the study site for both raised and traversable median treatments. The equations used, as shown in Table 3, are based on field studies and accident data for 50 locations

Virginia.

in

current

It is well

year

suggested

also desirable to year, to dete-rmine if the the 20-year period. over

the estimates be made for the In some cases, it is year. year, say I0 years from the current

that

design

the as other use one

as

future

design

median

remains

constant

other things being equal,• the median treatment with the predicted accidents per mile is the preferable alternative.

All lowest

Table

3

Regression Equations

for Predicting Annual of Accidents Per Mile

Annual

AI =

8.040 12.718.

AI

Annual

t =

5.432

28.797.

accidents

Sig

+

(R 2

0.00155

+

(R 2

mile ADT-

for

raised

0.0228

Dr-

median 0.00000926

Pop.

0.73.)*

accidents

Sig

per

Number

per

0.00173

mile ADT

for +

2.157

traversable

St

+

median

0.0000058

Pop.

0.71o)• De lay• An!lys •is

shown that the median type, whether raised influences the overall travel time for through or traffic. The median type does, however, influence the time motorists are stopped while waiting to turn left from the median. Therefore, the delay analysis considers only mid-block, left-turn delays. Based on the data collected during the field studies, the regression equations, shown in Table 4, for predicting midblock, left-turn delay (seconds per vehicle turning left) for It

has

not

been

traversable,

each

the

median

treatment

All other things lowest predicted

were

developed.

being equal, the median treatment with mid-block, left-turn delay is preferable.

•"•R 2 is the explained variance,

i.e., 73% of the variance in the accidents per mile is explained by the independent variables, e.g., number of signalized intersections, ADT, etc.

Table

4

Regression Equations for Predictine Mid-Block, Left-Turn Delay Mid-block, left-turn de lay (seconds

LTD

raised 1.362

median

Sig

2.937.

+

R

0.0184

+

2

0.205

DHV-

left-turn delav traversable median

0.525

Sig

0.920.

+

R

Omen-

vehicle) Pon.

0.0000332

0.73.

Mid-block, for

per

0.0198

+

2

DHV-

(seconds 0°0676

her

Dr-

vehicle) 0.0000214

Pop.

0.75.

Economic

Analysis

For many highway projects an economic analysis is conducted aid the decision makers in selecting among project alternatives. Alternative median treatments may be, among other desizn alternatives, selected for economic analysis. to

For

project,

every

construction

the

be

Raised

Median

specific cost typical costs are

of

of

costs

right-of-way, utilities,

and

estimated for each alternative. In lieu items for an individual project, the following suggested for use in the economic evaluation.

should

Traversable

:

Median

Accident and delay savings, sidered in the analysis.

should

$600,000/Mile $500,000/Mi!e be

among

the

benefits

CON--

method for conducting an economic analysis is In fact, the decision suggested as a result of this research. analysis of whether an economic should be conducted is an option left to the designers or traffic engineer. The ma•or emphasis of this guide is to provide an estimate of the accident and delay characteristics of several median alternatives, thus enabling the designers to select the treatment offering the best If the designer .wishes to conduct an economic safety estimates. analysis to further determine which treatment is justified, should be followed. current Departmental practices No

specific

Considerations

Other

If, after calculations

of

accident

statistics and determination or

operational

choice of been made no is advantages neither assumed have to treatment type, then Neverthe other, and either type may be selected for design. over .considered before theless, there are several factors that should be guidelines suggested. The following the final decision is made. are

delay

is

there

have

clear

median

I.

stopping sight distance is less than the safe computed by AASHTO standards anywhere on as the project• a traversable median should never be used section, unless the sight distance can be on the increased above acceptable limits. If-the

distance

2. 3.

medians

Raised

the

where

should

not

operating speed

Generally, raised medians following conditions"

points

(a) Access sections

where

be used exceeds are

on

45

roadway

desirable

can

streets

mile

greater

(b)

The 12.

(c)

Large volumes of pedestrians frequently the roadway throughout the section and be

number

confined

of

to

per

the

under

major interbe provided.

limited are crossovers

to

sections

mph.

is

than cross

cannot

crosswalks.

(d) A grid pattern of intersecting streets permits circuitous flow of traffic without disrupting traffic in residential communities. 4.

Generally,

following

traversable conditions-

(a)

The

number

of

streets

(b)

The number than 50.

of

driveways

(c)

A reversable

lane

traffic, is needed 5.

medians

Generally, Figure 4, one

side

per

are

desirable

mile

per

mile

is

less

under than

the

12.

is greater

for carrying peak-period in the near future.

the alternating left-turn should be used when access of the road.

lane.s, is not

in as shown needed on

median lanes, as shown in Figure 5, operational advantages over other no or median treatments and should not be selected for implementation due to their right-of-way and construction

Genemally, offer

continuous

safety

costs.

o_f. M_.e..dian•ype The accident and delay evaluations, along with the other considerations outlined in the previous sections, are intended to aid the designer or traffic engineer in the selection of a median treatment. Examples of the selection process are given

Selectio

in the

n

section.

next

EXAMPLE

APPLICATIONS

OF

THE

GUIDELINES

purpose of illustraZing the methodology, three exampmovided The input data as well as the results of below. are analysis are provided for each example. An interpretation of analysis data and the conclusions are also pmesented. Fore the

ples the

the

Example 1 A 1.402 mile, two-lane, urban arterial street carrying 12,040 vehicles per day (1,204 during the .peak period) is scheduled for widening. There are 3 signalized intersections, 4 streets, and 86 driveways on the highway. It has been estimated that 13 openings will be required if a raised median is utilized. The population of the area is 127,109 persons; however, in the design year the population is expected to be 138,000 persons. Traffic volumes are expected to be 21,100 vehicles per day (2,110 in the peak period) by the design year. Also, it is anticipated that 2 new signals will be installed on existing public streets along with ii new driveways. No new streets are anticipated. Program MEDEQU, shown in the Appendix, was utilized to provide estimates of the safety and operational character{stics for raised and traversable median design alternatives. The results of the accident and delay analyses are given in Table 5. Based on the-accident results, a traversable median should be selected; however, the mid-block, left-turn delay statistics slightly favor a raised median. The pedestrian volume in the area is very low and circuitous routing of traffic on existing streets is not possible.

ii

Tab le

Estimated

Delay Impacts

Accident •nd

Annual

Number

Condition

of

Accidents

Raised

Existing Design (20 Years)

Mid-B.!ock

5

Left-Turn

Condit ion

Per

Mile

20.57

9.07

45.83

32.45

Delay

i

Traversable

Seconds

Raised

Existing Design

Example

for

Tray

Per er s

Vehicle able

16.06

16.77

(20 Years)

30.42

33.19

safety impact

providing a important factor

traversable median on this in this case. For example, roadway section is an if the traversable median were constructed today, the annual number of accidents on the 1.402-mile section is estimated to be 13 By compari(1.402 mile x 9.07 accidents per mile = 12.72 • 13). of number annual the constructed, raised median if were son, a accidents expected is 2.9, which is more than twice the number of Moreover, in the accidents anticipated with a traversable median. design year it is estimated that the traversable median will have 30% fewer accidents than the raised section (45 accidents on the traversable section compared to 64 accidents on the raised section, Over the 20-year design peried of 19 accidents annually). a savings traversable section. accidents the expected fewer 360 on are The

of

of all facters clearly suggests that a two-way, traversable median design should be selected for the A summary of the analysis is shown in Table 6.

Consideration left-turn

project.

12

Table

Summary

Existing roadwayProject length Estimated

of

Results

Two-lane, two-way

I

arterial

street

for"

Raised

Median

Traversable

( 20

Year Year years )

29

13

64

45

940

58O

Section

accidents

Total over

the

design period mid-block,

left-turn

Raised Median Current Year

Design Other

Example

annual

Design

(20

for

1.402 miles number of accidents

Current

Estimated

6

delay,

16.06

per vehicleTraversable Section 16.77 seconds

Year

years)

30.42

33.19

considerationsi.

Stopping sight

distance

Greater be

will

Suggested posted speed

45

limit

points

Access

Circuitous Estimated

crossing

limit intersections

due

flow Less per

access

than

day.

Access

points

I00

major

to

access

to

driveways Existing streets do provide circuitous

pedestrian

points

ft.

mph

Cannot

routing

volume Distribution of

than 1,000 provided.

numerous

not

traffic

crossings

is

required

on

both

sides

at

numerous

of

the

road

Right-of-way availability

R/W width should not exceed 70-ft. to avoid acquisition of business units.

0the•

None

factors

13

Table

6

(continued)

RecommendationThe estimates of the accidents expected on the project cl-early indicate that a traversable median section offers significant benefits over a raised median section. Consideration of the physical features of the site and vehicle and pedestrian volumes provides supporting evidence that a continuous two-way, left-turn median lane with four ll-foot lanes (total of 5 lanes) be selected for this project•.

Examp le_ 2 0.786-mile section of a three-lane The existing considered for improvement. A

Table

roadway is being

suburban

conditions

are

given

in

7. Tab le

7

Existing Roadway Conditions Item

Number

Signalized intersections Public streets Driveways Proposed median openings Avemage daily traffic Amea population Design hourly volume (peak-hour volume)

I 3 84 8

for

Example

Number

Per

2

Mile

1.27 3.82 I06.87 i0.18

9,860 118,000 986

designers

informed that considerable commercial in the area during the next 20 years. Because of growth potential the designer obtained estimates of roadway conditions for both a 10-year and a 20-year (design year) period. Input from the transportation planner, district traffic engineer, central office traffic safety engineer, and the assistant resident engineer were used to obtain the estimated conditions projected in Table 8. The

development

has the

have been been planned

The data shown

to

provide

block delay The results

in Tables 7 and 8 were used in program MEDEQU of the annual number of accidents and midfor existing conditions and the I0- and 20-year periods. of the analysis are shown in Table 9.

estimates

14

Table

Estimated

8

Roadway Conditions

Signalized intersections streets Driveways Proposed median openings Average daily traffic Area population Design hourly volume Public

17,230 128,000 1,723 Table

Accident

Annual

Condition

Existing ! 0 year

Design ( 20

and

Existing .I 0 year

Design (20

*it

year)

Per

not

the

Mile

4!.92

•6.05

Delay

Seconds

Raised 13.35 26.64 Unable

to

15

2

Traversable 2.71 20.90

Traversable 10.03 23.50 Est

:'•

possible to estimate values estimated result is out of Program MEDEQU provides this

is

cause

values.

Accidents

Raised 9.25 20.28

Left-Turn

24,600 134,000 2,460

9

Delay Impacts for Example of

Number

year)

Condition

2

Number Per Mile I0 Years 20 Years 1.27 2.55 6.36 8.91 120.87 120.87 10.18 i0.18

Number i 0 Years 20 Years I 2 5 7 95 95 8 8

Item

Estimated

Example

for

Unable

for

to

this

Est

•

condition

the range of known check without user

b•-

input.

accident

The

results

of

!.

For

current

the

the

significantly the

than

2.

The

area

raised

analysis indicate that"

year, a traversable section has fewer accidents per mile per year

section

(2.71

compared

development anticipated

and

to

the

9.25).

projected

traffic volumes suggest that ten years from now there will be little difference in accidents per mile between a raised and a traversable section (20.28 compared to 20.90 accidents per mile). years from now (the design year) a raised section will have significantly fewer accidents per mile than the traversable section (41.92 compared to 46.05 accidents).

Twenty

3.

analysis clearly indicates that as site and volume condichange, the choice of a median treatment changes. This example provides an interesting but practical problem that must be faced when interpreting the results and selecting a specific median treatment. Before a median type is selected, the remaining analysis, as outlined in Example I, Table 6, must be completed. It should be evident that factors such as stopping sight distance access point distribution,.circuitous routing, etc., also important factors for consideration in the choice of a are The

tions

median

treatment.

In this case, the minimum stopping sight distance for a 45 mph anticipated operating speed could not be provided at a feasible Because of the accident benefits anticipated in the design cost. and the sight distance problem, a raised median section was year chosen for the project.

•xamp,!• 3 A 2.477-mile section of a four-lane undivided roadway located in an urban fringe area has been selected for reconstruction. A review of the existing physical and operational characteristics of the site indicates that the project should be divided into three

*It

is

guide

support

suggested in

that

a

determining if

the

selection

10%

of

the

difference in accidents be used difference is important enough

one

treatment

16

over

the

other.

as

to

a.

sections. The first section is 0.544 mile in length and ties into an existing four-lane highway with a raised median. Section in length and has considerable commercial detwo is 0.681 mile velopment on the west side of the roadway and residential developPedestrian volumes in excess of 500 per ment on the east side. at three major sections; not cross at crosswalks.

however, a large The third section is 1.252 miles long and encompasses an area of predominantly residential streets. The existing roadway conditions are shown in Table I0. An example of using these input data for MEDEQUare A-5 through A-7 and the results shown program on pages hour have number of

are

been

given

on

is

It

observed

pedestrians

page

the

do

A-9.

of the design team that moderate to low the project corridor. Thus only the projected The made. roadway condiwere in Table ii. year are shown

consensus

growth can be expected in 20-year design estimates tions

for

design

the

Table

Existing Roadway

i0

Conditions

for

Example

Section

Item

Number

i

Length, miles

Signalized Public

0.681

2

3

12 •I

I0 67

6

7

streets

Driveways Proposed

median

openings

Average daily traffic Area population Design hourly volume (Peak-hour

volume)

2

0.54•*

intersections

22,716

16,87 0 22,716

1,522

1,687

15

220

lengths of 0.35 mile or less should not roadway conditions are greatly affected by which produce erroneous results.

*Section the

17

3

3

1.252 5 15 121

13

17

900

22,716 1,790 be used because short sections

Table

ii

Projected Roadway Conditions

Length, miles Signalized intersections streets

Driveways Proposed median openings Average daily traffic

population Design hourly volume

Area

Ii, the

3

Number

1

2

3

0.544

0.681

1.252

3

5

5

12 58

i0 68

6

7

15 121 13

22,700 53,100 2,270

program }•EDEQU and the input estimates of the safety and delay results are shown in Table 12.

Utilizing and and

Example

Section

Item

Public

for

23,800

23,100 53,100 2,310 values

impacts

53,100 2,380 from were

Tables

computed

i0

annual number of accidents per mile, a raised The median treatment should be selected for sections i and 3. sections benefits these raised median treatment has safety on A raised median is under existing as well as design conditions. section 2; however, also desirable for existing conditions on different, the design year estimates are not significantly 79.33 • 82.39.

Based

on

the

consideration of the safety, delay, and specific data, a raised median treatment was selected three sections. Based

on

18

other sitefor the

Table

Estimated

Accident

Annual

and

Number

12

Delay Impacts for Example of

Accidents

E,xis t_i_n•g Section

Per

Design

Conditions Raised TPaversable

3

Mile

Conditions

Raised

Traversable

Number I 2 3

38.11

64.97

46

=S

43

44.69

88

49.55

LeftrT,urn D,ela•. _Second..s. Section Number I 2 3

Raised 22.91 25.11 27.56

87.73 82.39 59.58

63.93 79.33 53.56

•e f t_- Tu r n• De _lgy

•

Traversable

Raised

Traversable

22.30 24.87 27.25

3S.16 31.57 Unable

19

to

s

e c

o_ _ _ n d__s

34.62 34.92 Est

Unable

to

Est

REFERENCE I

S. Department of Transportation, tration, Manual on Uniform Traffic and Highways, Washington, D. C.

U.

21

Federal Highway AdminisControl Devices for Streets

APPENDIX PROGRAM URBAN

MEDIAN

Keypunching.

MEDEQU DESIGN

Guide

This program contains a set of equatio• w•±cn compute accidents per mile and left-turn delays for several sections of a median design project A listing of the program is presented in Table A-I. first

The

county, to

be

format,

tains

ADT, and

data

district, processed. and

card

card

contains

project number,

Table column

A-2 shows numbers.

the and the

project information" route, the total number of sections input variables, their type,

Each remaining card. corresponds to a project section and consection numbers, signals per mile, these equation variables" mile, driveways streets per per mile, area population, DHV, median openings per mile. Data

are

to

be

punched from

the

formatting sheet, Figure

A-I.

The only variables on the formatting sheet which are to be punched enclosed in boxes. Column numbers are below the first box of are each variable and decimals appear where they should be punched. Please note that section humber, ADT, population, and DHV do not have an input decimal point. Also, other sections would be continued on the following sheets. A-2. are

when

Figure A-3-gives the output for the sample cards of Figure Notice that the project•labels (route, county, and district) left-justified. All other variables should be right-justified punched. In this example, three roadway sections are being

considered.

Table

Listin• C C C C C C C C C C C C C C C C C C C C C C C C C C C

PROGRAM

FOR

USE

Program MEDEQU

TYPE

IN MEDIAN

SELECTION

I.NPUT

ROUTE COUNTY DISTRICT PROJECT NUMBER NUMBER OF SECTIONS

CARO i

(