lional Bureau of Standards

Library, H.W. Bldg ^

JAN 1 61961

PB 161620 NBS

^ecknicctl ^Txote 119

COMPUTER SIMULATION OF

STREET TRAFFIC

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

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NATIONAL BUREAU OF STANDARDS

technical cylote

119 NOVEMBER 1961

COMPUTER SIMULATION OF STREET TRAFFIC

M. C. Stark

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Depart- ment of Commerce, Washington 25, D. C.

DISTRIBUTED BY UNITED STATES DEPARTMENT OF COMMERCE

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Price $2.25

TABLE OF CONTENTS

Page

ABSTRACT ..... 1

1. PURPOSE OF THE STUDY 2

2. HISTORY OF THE PROJECT 3 Concept of More Sophisticated Model . 3 Selection of 13th Street Site 3 Phase Completed 4

3. DESCRIPTION OF THE METHOD

Use and Numbering of Unit* Blocks . 4 Quarter Second Review Cycle 5 Printout Tables 5

4. ANALYSIS OF RESULTS 5

5. CONCLUSIONS 7

6. AREAS FOR FURTHER RESEARCH 8 A. Immediate Results 9 B. Intermediate Results 9 C. Longer-Range Tasks 10

7. THE COMPUTER PROGRAM 10

8. DETAILS OF THE PROGRAM 11 Search Routine 1 "A" Layout and "B" Layout 1 Generation . 1 SEAC Display 1 Permissible Speed 1 Sight Distance 12 Irregular Unit Blocks 12 Turns . . . . 12 Lane Preference . 13 Simple Turn . 13 Turn Bias and Last Chance 13 Traffic Signals . 13 Stop Signs 14 Move Routine 14 Additional Details 14
TABLE OF CONTENTS (Continued)

Page

9. IMPROVEMENTS IN NBS SIMULATION II OVER

SIMULATION I 15

10. ASSUMPTIONS AND PARAMETERS ......... 16

11. ACKNOWLEDGMENTS 18 LIST OF TABLES

Table Title 1-1 Summary of Cars Generated by Street and

by Hourly Rate 19 1-2 Summary of Cars Generated by Generation

Point and.by Cycle 20

2 Summary of Station B Counts 21

3 Summary of Vehicle Retirement Data 22
LIST OF FIGURES

Figure No. 1 Title Page

1. 13th Street Layout '. 23

2. Generation Points and Unit Block Numbering . . 24

3. Exit Numbers and Station B Check Point .... 25

4. 13th Street as Shown on Oscilloscope 26

5. The Two-Word Format 27

6. Turns From 13th Street into Girard Street • • 28

7. Turns From Girard Street into 13th Street • • 28

8. Left Turn Exercise at 13th and Girard Streets- 29

9. Design Volumes 30 Summary of Design Volumes for Entrance Into Model 31

10. The Basic Forward Move 32

11. 13th Street Signal Timing Diagram 33 Signal Timing Data for 13th Street 34-35

12. Pattern of Last Chance Unit Blocks 36 Table of Successive Car Positions in Left-Turn

13. Exercise 37

14. Unit Block Turn Sequences at 13th and Girard Sts. 38

15. Jump-Stopping Distance -Goal Points Table ... 39

16. Characteristics by Type of Vehicle 40

17. Conditions for Conflicting Turn 41

18. Numbering and Location of Diagonal Unit Blocks 42

v
LIST OF APPENDICES

Appendix Title Page

A Generation Table 43-49

B Station B Count • 51-54

C Vehicle Retirement Table 55-57

D Marked Car Chronological Printout 59-66

E The Basic Forward Move 67 F List of Routines 68-70

G The Two-Word Format 71-73

H Illustration of a Simple Turn 74-75

I Left Turn Exercise at 13th & Girard Streets 76-77

J Traffic Signal Package 78 K Conditions for Turn Under Conflict 79 L Detailed Movement of Marked Cars ..... 80-81

M Flow Chart of Stop Sign Routine 82-83

N Flow Chart of Move Routine 84 O Terms # .... 85-87

P List of Simulation Runs ... 88
COMPUTER SIMULATION OF STREET TRAFFIC

Martin C. Stark

ABSTRACT

This Technical Note describes a digital computer simulation of vehicular traffic on a section of city street. The study was made for

the Bureau of Public Roads by the Data Processing Systems Division,

National Bureau of Standards, over a period of three years, from July 1958 to June 1961. The narrative of the report is presented first, followed in order by the three summary Tables, the Figures, and the Appendices. The latter contain text which goes into greater detail and

which, in many instances, also refers to the Figures.

An element-by-element computer simulation of the volume and

movement of traffic on a nine -block section of 13th Street N. W. , in Washington, D. C. is described. A stochastic process is used, in which

the input parameters defining the operating and physical characteristics

of the cars are controllable within narrow ranges. The computer

reviews each simulated car every quarter second and moves it according

to rules for movement which are applied by 37 main routines and subroutines of the computer program. . The simulation run on the computer produces two outputs: The

quarter -second car positions are plotted on an oscilloscope and photographed, which result in a moving picture like an animated cartoon,

so they can be seen in real time. The effect is comparable to viewing

the traffic flow from a helicopter. The other output is a series of tables issued by the computer. These tables catalog all vehicles as they enter the model, clock and count them as they pass a key inter- mediate point, and finally, check them out at the end of the course,

counting them again and noting their individual running times. Other

information is also furnished, such as type of vehicle, speed, and lane

use. The tables thus furnish an abundance of quantitative data for measuring and evaluating the performance of the model.

Arbitrarily changing the input parameters in the simulation model

will permit predictions of the resultant running times and capacities if the proposed changes were really made on the street. With the completion of this initial, specialized, working model a solid groundwork has been laid for further research effort through

refinements, extensions and generalizations of the ideas and methods

presented.
1. PURPOSE OF THE STUDY

The purpose of the work reported here was to simulate the volume and movement of cars with a digital computer, using as the

test site a real location where abundant field data were available for control and checking purposes. The test course selected was a nineblock section of 13th Street, N. W. , Washington, D. C. , from Euclid

Street to Monroe Street. A standard computer -simulation technique involving the use of random numbers "generates" cars at each entering lane in such a manner that the total number entering at each point over a period of time has an assigned expected value. Each car is moved every

quarter second according to detailed "rules of the road" built into the computer program.

Successive car positions have been plotted on an oscilloscope

and photographs taken so that the simulated operation can be viewed

from moving pictures. The effect is comparable to the observation of

traffic over a stretch of several blocks as if by helicopter. Printout

tables furnish detailed quantitative data about the volumes, running

times and characteristics of the cars involved.

To the extent that the simulation model can be made to resemble

the known real conditions, we may infer that if the volumes and

characteristics of traffic and the operating rules were changed in the model, the results of a run would represent a prediction of what would

happen on the street if the indicated changes were really made. The

quantitative operational values to be sought relate to delays, running

times, and capacities which can be handled within prescribed levels

of delay.

It should be borne in mind that a single run represents only a sample of results derived from the situation being simulated. If the run is for four minutes, the reliability of the results would have the same limitations as taking only a 4-minute count on the street. The

strength of the results can be improved by lengthening the run or by

having multiple runs and consolidating the output data. The immediate area of application of this simulation device

relates to the use and timing of traffic signals. Simulation runs can

be made to study the sensitivity of the traffic flow to altered signal

settings, to measure the effect of changed offsets, cycle length and

splits with a view to arriving at optimal timing and to explore the capacity of the signal system to handle different patterns or increased

volumes of traffic. The use of a generalized model can be extended to many other

traffic engineering situations such as use of one-way streets, banning

of left turns, location of bus stops, and restriction of parking.
2. HISTORY OF THE PROJECT

The late Professor H. H. Goode of the University of Michigan was one of the first persons to stress the possibilities of digital

computer simulation as an aid to engineers in solving traffic engineering problems! *). A simple model constructed under his direction was

based on the crossing of a pair of north- south streets by a pair of east- west streets. Each street carried a single lane of traffic in each

direction. When cars moved they all moved at the same speed. When

moving, a constant minimum space was required between them. When

stopped, the cars could be close together. The four intersections were

signalized. In the moving picture display, a symbol adjacent to each

intersection indicated the signal message (a bar in a straight position

for Gc, in a cross position for Stop, at a 45° angle for Amber).

Cars would turn right, left or go straight by reference to a random number comparison at the moment the car entered the intersection. A left turner would wait in the intersection if necessary,

blocking its followers, until opposing traffic offered a certain gap.

In the computer model each of these cars was represented by a

single bit. Thus all cars were regarded as alike and were processed

uniformly.

Concept of More Sophisticated Model

It was Goode's idea that instead of describing each car by only one bit it would be possible to represent each car by a whole computer

word. In this way the car could be assigned individual characteristics

as to speed, type and destination. The Bureau of Public Roads entered into an initial agreement

with the National Bureau of Standards in July 1958 under which NBS

would develop a considerably more advanced simulation model,

utilizing several of Goode's concepts. For control and checking

purposes it was desired that a real location be selected for which

abundant field data were already available. Selection of 13th Street Site The test site selected was a section of 13th Street, N. W. , Washington, D.C. , from Euclid Street to Monroe Street. The length

of the course is 3, 240 feet, including nine blocks. Seven of the intersections are controlled by traffic lights, three by stop signs.

nr Goode, H.H. , and Pollmar, C.H. , and Wright, J.B., "The Use

of a Digital Computer to Model a Signalized Intersection, " Proceedings of Highway Research Board, vol. 35, 1956, pp 548-557. ~
(See Fig. 1. ) The operation relates to the peak hour of the afternoon,

rush, when the four lanes of 13th Street are operated one-way

northbound.

By early I960, the NBS effort had produced a first model,

complete with a movie but lacking printout tables for quantitative

evaluation. This model, which we refer to as NBS Simulation I, carried out most of the original objectives. It was, however, in- complete in various respects. Principally, it generated no cross

traffic. (Traffic turning onto cross streets however was carried away. ) A flaw in the program permitted cars at one location to be

swallowed up by other cars. Some cars trapped behind slow moving

leaders fluttered wildly from one lane to another attempting vainly to overtake. Other correctible defects were observed.

The second work program by NBS was begun in July I960 and was

completed a year later. The effort resulted in the present, greatly

improved Simulation II, which is the principal subject matter of this report.

Phase Completed

The phase of the work now terminated has considered all the items that were formally presented and has successfully carried out nearly all of them. It is believed that for practical purposes we now

have a specialized model that is, or can be readily made to be, a

solid basis for further research effort.

3. DESCRIPTION OF THE METHOD

Use and Numbering of Unit Blocks

Each lane of each street is divided into 12 -foot sections called

unit blocks. Computer storage reserves a place for information about

each unit block (abbreviated UB). If there is a car in a UB, full information about its exact location and its physical characteristics

is stored. Another portion of the storage word furnishes any

necessary information about the road at that point. This dual role of the UB is extensively described in Appendix G. The UBs are numbered consecutively wherever possible. This

facilitates a systematic search of successive UBs for cars to be processed as well as an orderly movement of each car from one UB

to the next higher numbered UB. Fig. 2 shows the basic numbering

plan for UBs. Turns use diagonal UBs superimposed on the basic

grid. The turn UB layout is shown in several other figures,

especially Figs. 6 & 7 relating to 13th and Girard Streets. (See also

Fig. 18.)
Quarter Second Review Cycle

The time cycle for searching all UBs for cars, moving the cars, generating new cars and preparing any outputs is one quarter second

of simulated real time.

Traffic inputs are generated (using random numbers) to represent assumed input volumes. Every quarter second, the IBM-704

program moves the cars according to "rules of the road" built into the computer program. The coordinates of the car positions and the

traffic signal settings are written onto a magnetic tape output. This

tape is later fed into SEAC (a specialized NBS computer), which is equipped with attachments and facilities for projecting the coordinates

onto an oscilloscope and actuating the trigger of a camera in order to produce a series of photographs capable of being processed into a

real-time moving picture film. Printout Tables

The 704 program which moves the cars also prints out detailed

data which describe the generated cars, count and clock the cars as

they pass an intermediate check point along the course and finally

check out the cars as they finish the test course. These three tables (Appendices A, B and C) furnish a full "case history" of the cars

involved. Cars can be traced through the course; their physical

characteristics are noted; their individual running times and

performances are recorded.

The moving picture provides an overall view of the general

performance of the fleet of cars. The tables provide specific,

detailed, quantitative data by which to measure and judge the performance.

4. ANALYSIS OF RESULTS

Several simulation, runs have been made. (See Appendix P for a list of the runs. ) Run No. 3, of four-minute real-time duration

(three complete 80- second signal cycles), has been selected as

typical and will be described in considerable detail in later sections

of this report. A moving picture was made of the oscilloscope display.

The computer produced printout sheets furnishing detailed numerical

data to permit analysis of the behavior of the simulated cars. From

this information three summary tables have been made which are described below.

Table 1 summarizes the count of cars generated during each

cycle for each of the generation points. The figures are shown by

each cycle, summed for the four minutes and expanded to an hourly

volume. It will be noted that the volume of simulated cars entering

the model at the Euclid Street entrance to the 13th Street test section

is 2, 910 cars per hour. This compares with a field volume of 3, 050.
(See Fig. 9.) The principal cross streets, Harvard Street, Columbia

Road and Park Road, carried 330, 600 and 780 simulated cars per hour compared to the field values of 708, 668 and 670, respectively.

The poor correspondence for Harvard Street presumably is due to the smallness of the sample. In the long run the number of simulated

cars, by design, should tend to equal the field values. Because of concern about the Harvard Street generated volume, Run No. 4 was

scrutinized as an essentially parallel run in the Monte Carlo method.

While not otherwise summarized in detail, Run No. 4 showed

generated traffic, expanded to an hourly rate, of 780, 720 and 585

cars, respectively, on the three principal cross streets, Harvard

Street, Columbia Road, and Park Road.

The field data are traffic counts made over a period of time in 1954-55 by the District of Columbia Department of Highways and the Bureau of Public Roads, and documented in an article entitled "Capacities of One -Way and Two -Way Streets with Signals and with

Stop Signs", by Alexander French, February 1956, Vol. 28, No. 12, PUBLIC ROADS.

It is assumed that care was exercised in sampling the traffic at that time and that the results set forth are reasonably representative

of the then-existing conditions. Nevertheless, a general note of warning should be sounded to the effect that any deficiency in the representation of a prototype situation being simulated will be carried over into the simulated model and will introduce error into the results of any analytic or predictive simulation runs. Simulation can never be a substitute for sound basic data. In the present study the problem of validation may be even more difficult because of the passage of time. Validation of the model for 1955 traffic conditions

may be indicative, but is no guarantee, of validation under presentday traffic conditions.

The significance of Table 1 is that it provides a rough check on

the "car generating" procedure. Table 1 represents the traffic "inputs". Tables 2 and 3 (to be described) represent "outputs" and

are the means for measuring the performance of the simulation.

These tables provide a verification that traffic moves through the model in reasonable correspondence to the known situation in the field. Table 2 shows the results of a count at Station B which is on

13th Street just north of Lamont Street. (See Fig. 3.) This is the heaviest point of the test course. In the model, the expansion of the four -minute count at Station B produced an hourly volume of 3, 330

simulated cars. This is comparable to the field volume of 3, 168 cars per hour.

Table 3 relates to cars leaving the end of the 13th Street test course north of Monroe Street. Again, the simulated cars are

counted by cycles and by lanes, and are expanded to an hourly rate of

2, 400. The field figure at this point is 2, 691 cars per hour. Table 3 also records the running times of those cars which have traversed the

6
full length of the test course from Euclid Street. In the first cycle

when the model contained somewhat fewer cars, the average running

time was 364 quarter seconds. In cycle 2 it was 444 and in cycle

3,464. The average time over the three cycles was 437 quarter

seconds.

Incidentally, the traffic signals on 13th Street, during the P. M.

rush hour, are set for a speed of 26. 8 miles per hour. The average

running time of the simulated cars of 437 quarter seconds reflects an

average speed of 20. 2 mph. A running time of 330 quarter seconds is required to stay in pace with the signal progression.

Tables 1,2 and 3 are summaries of full computer printouts

which are photographically reduced as Appendices A, B and C,

respectively. The basic printout sheets identify individual vehicles,

thus making it possible to trace through the movement of any particular

vehicle.

5. CONCLUSIONS

A working simulation model of a particular, fairly complex

traffic location has been constructed. A computer program causes the cars to behave in what seems to be a realistic manner. The cars stop

at red lights; they yield the right of way at stop signs; they maneuver

into correct positions for turns; they move at different speeds; they

accelerate and decelerate; faster cars shift lanes to overtake slower

cars; they form queues; and they do most of the definable things that cars can be expected to do in city traffic. The results in no sense indicate a rigorous validation of the model. Up to the present point, reasonableness is the only criterion

for judging the performance. Approximately the correct number of cars are accounted for at key points; their characteristics as to speed

category, type of vehicle and intended turns correspond with known

input data; their average running times are expectedly somewhat

slower than that required to keep up with the progressively timed

traffic lights.

It may be significant that the speeds and running times become

slower as the simulation progresses from cycle 1 to cycle 2 to cycle 3. Although the model was "filled" with cars before the beginning

of the run, it had been filled just prior. The lengthening of the running

times may be caused by the fact that the full effect of congestion takes

a little while to set in. To get more information bearing on the validity of the model,

two steps may still be taken. One is to study the movie display carefully to see whether a "helicopter" view of the cars verifies that they are performing correctly. The other is to compare the simulation

running times with actual running times from the field, perhaps by a

field check of license numbers of cars traversing the course or by a

series of runs through the course using the "floating car" method.

7
(In the latter method, a test car is driven through the course a number

of times with the driver trying to drive neither faster nor slower than

the average car in the traffic stream.

)

A point worth bearing in mind is that even though the simulated

running times may not be entirely valid in total, a difference in running time to reflect a changed parameter may be highly significant.

The reverse is also true. A particular detail of the simulation may

not check completely with reality and yet the total result can still furnish a useful measure. Ideally the simulation would correspond

with reality both in detail and in total, but it has value even if one of these objectives is not immediately accomplished.

6. AREAS FOR FURTHER RESEARCH

The question remains: What constitutes validation of the model?

So far the test of reasonableness is the only criterion that has been

applied. When the performance of the model is accepted as corresponding reasonably closely with actual field conditions, it will be

possible to change the parameters and study the new results. From

a practical point of view it is the ability to test untried conditions and

to make predictions of likely results that will be the real payoff of simulation as a tool for traffic engineers.

Beyond the immediate objective of getting practical answers for

13th Street are several broader objectives. Study should be made of how to generalize the model in various ways. A model should be

made where the main street is two-way rather than one-way.

Additional features should be added such as random delay factors,

standing vehicles, bus stops, wider range of speeds and acceleration

rates, pedestrians and additional count stations. Study should be made of what is required to make the model

applicable to other locations by plugging in different basic data at key

points in the program.

An output editing routine is an important future requirement. A

computer is capable of putting out a vast amount of paper. The

present program is no exception. In order to facilitate an expeditious use of the model to develop useful results, a routine should be

written that will summarize the output data at several levels of detail.

In the present study the important answers center around running

times, delays, and street capacities.

Another area of study is the question of how fine the model needs

to be in order to furnish good answers. The present model is very

fine. The basic time unit is one quarter second and the basic distance

unit is one -hundredth part of 12 feet (1. 44 inches). These small

units lead to an enormous number of computations even for a highspeed digital computer. To what extent, if at all, would the useful- ness of the results be jeopardized if the model used larger time and

8
distance units? In order to answer this important research question,

it is necessary to use a model which is capable of a fine breakdown.

To seek an answer to this question using a coarse model would be

impossible. The usual technique in solving this kind of problem is first to try a gross unit, then try a unit half as large, and then halve

it again. This method will fairly quickly locate the general area where

the optimal value lies. In looking ahead to further applications, proposed tasks may be

considered in three categories: Those that can be done practically

immediately, those that will require some changes and rewriting of the computer program and those of longer-range nature that may

require fairly extensive changes in the program.

Representative tasks for future research effort are listed below

arranged in the three categories of required time and effort: A. Immediate Results

1. Change volumes, turn ratios, lane distributions, traffic signal settings, desired speeds, percent of trucks,

acceleration rates, for the specific 13th Street course.

2. Modify certain rules of behavior (such as those involving

clearances, lane preferences, acceptable gaps, response

to amber signal, overtaking).

3* Plant cars to depict a study condition such as the following:

a. Plant a stalled car and see what happens.

b. Set up a solid line of cars to study the wave action.

c. Set up a conflicting turn situation. Intermediate Results

1* Prepare an editing routine that will summarize the computer

output data at several levels of detail.

2. Substitute signalized control for stop sign control (or vice

versa) at any intersection, and study the results.

3. Change any cross street from one-way to two-way (or vice

versa).

4. Substitute a yield sign for a stop sign.

5. Put in additional count stations to measure volumes and

delays at more points.
6. Provide for buses which would stop at prescribed bus stops.

7. Interject random delay factors into the performance of the cars.

C. Longer-Range Tasks

1. Make 13th Street two-way (as it is in non-rush hours).

2. Study problem of generalizing the computer model so that, by merely "plugging in" proper data regarding physical

layout, it can be made applicable to another set of streets.

3. Study the effect of making the model less fine (by using

larger space and time units). In addition to the representative specific tasks listed above,

further effort should be accompanied by a broadening of the scope of

the work with the purpose of promoting an interchange of information,

acquainting traffic engineers and administrators with what has been

done to date, learning what additional problem areas lend themselves

to treatment by simulation techniques, and creating a wider interest

and challenge for further research.

7. THE COMPUTER PROGRAM

The basic working program for the IBM- 704, including the working constants and the input parameters, contains about 6000 words.

In addition, the "A" layout (two words for each of about 1800 UBs) uses

about 3600 words and the "B" layout another 3600. (The "A" and "B"

layouts are defined in Chapter 8. ) A table look-up of the coordinates of each UB and traffic signal for presentation by SEAC on the oscilloscope uses about 3700 words. The total requirement thus is about 16, 900

words. The 704 installation at NBS has 32, 768 words of primary core

storage so that no effort to conserve space was necessary. The

computer program was assembled using the SAP assembly program.

The final production run representing four minutes of real time

required 60 minutes of 704 time. Thus the ratio of computer time to real time was 15 to 1. In order to display all of the 13th Street test course

simultaneously in as much detail as possible on the oscilloscope it was found desirable to break 13th Street into two pieces. The first piece, from Euclid Street to Irving Street, appears in the left half of

the display and the second piece, from Irving Street to Monroe Street,

in the right half. (See Fig. 4.

)

10
8. DETAILS OF THE PROGRAM

Search Routine

The program searches methodically for cars to be processed.

Starting at UBO, the first UB in lane 1, the search continues through

lanes 1, 2, 3 and 4 of 13th Street, then the lanes of all the cross

streets and finally the diagonal UBs (for turns). "A" Layout and "B" Layout

The cars are found on what has been called the "A" layout. To

keep matters straight, because it is impossible to process all the cars

simultaneously, each car as it is processed is moved to its new

position on the "B" layout. For the remainder of the review cycle the car continues to appear on the "A" layout in its old position.

When all the cars found in the "A" layout have been moved to new positions in the "B" layout, the scanning is completed. Then the "A" layout is erased and the "B" layout becomes the starting point

for the next scan. Generation At the end of each cycle the car generation iroutine is performed.

If a car is generated, its characteristics are also determined including

its destination or "exit". (See Fig. 3 for key to exit numbers. ) A

newly generated car will be launched if this can be done safely. Otherwise it will be retained on a backlog list for the particular generation

point in question until it can be safely launched. (See Fig. 2 for map

of generation points.)

SEAC Display

The edit routine notes the positions of the cars and the settings

of the traffic signals, looks up the coordinates and writes the information on the output tape to be used later for the SEAC display.

Finally the clocks are advanced one quarter second and the program

is ready to repeat the cycle.

Permissible Speed

When a car is found for processing, virtually the first task of

the program is to consider the car's desired speed in relation to its present speed (last quarter second jump) and its allowable acceleration rate. Each car carries with-it an information package describing

various physical characteristics and details. The word format is pictured in Fig. 5 and described in detail in Appendix G.

11
Sight Distance

When the permissible speed has been determined (in terms of unit point jump per quarter second), the equivalent of required sight

distance is determined by a table look-up, Fig. 15. The program

then probes ahead attempting to achieve the "goal points" necessary

to satisfy the sight distance requirement.

Two prime considerations are whether there is a car ahead and

whether there is any irregularity about the roadway (such as a traffic signal or a turn). In every case the key to the information appears in the UB word format (Fig. 5) and can be found by systematic checking

of every UB involved (ahead, behind, right or left as required).

The considerations to this point are described in more detail in a later section, Appendix E, entitled the Basic Forward Move which

utilizes Fig. 10.

If the goal points can finally be verified, the stated jump can be

made (onto the "B" layout). If the goal points are not adequate, then

a table (Fig. 15) is consulted to determine what reduced jump can be

made safely.

Irregular Unit Blocks

During the processing, the program is constantly on the alert to comply with the requirements of any of the roadway "irregularities".

If a UB is responsive to a traffic signal, the program must check the signal indication. If there is a turn ahead, the program must test whether our car is intending to turn. If our car passes a count station,

it must be properly tallied and clocked. If our car reaches the end of a lane, it must be checked out. A number of other special situations may occur, singly or together. In general, each situation has one or more sub-routines which can be called upon to determine the proper move. Some of the routines are specific to traffic on the main street, some relate to cross traffic only, some handle cars in the diagonal

unit blocks (on turns), some are generalized. The scope of the routines can be realized by reference to Appendix F which lists and

defines briefly 37 main routines, sub-routines and table look-up

routines. The use of many of these routines is illustrated by later references.

Turns

An intersection is basically the crossing (usually at right angles)

of two sets of consecutively numbered UBs. The various possible

turns are represented conceptually by the superposition of appropriate

diagonal unit blocks to connect the lanes involved in each turn. In the model, turns from 13th Street are always made from the nearest lane. Thus turns from northbound to eastbound are made from lane 1 of 13th Street and turns from northbound to westbound are made from lane 4. 12
Turns from cross streets into 13th Street, however, may be

made into either lane 1 or lane 4. The rules, built into the program,

are as follows: If a turning car is destined to make a later right turn

(odd exit), it will turn into lane 1 without exception. Similarly, if it is destined t6 turn left later (even non-zero* ex£t), it will always turn

into lane 4. This rule applies to both right and left initial turns into 13th Street. Lane Preference

For those cars turning into 13th Street which will stay on 13th Street (zero exit), each car carries with it a lane preference (bit No. 34, see word format, Fig. 5) which was randomly determined

at the time the car was generated. The car will turn into the lane

of its preference except for one situation. If it is trying to turn left into lane 4 and must yield to opposing traffic (assuming the cross

street is two-way), it will relinquish its preference and proceed to the position for turning into lane 1. It will of course wait, there, until it can turn safely. These points are illustrated in Appendix I entitled "Left Turn Exercise", and in Fig. 8.

It is seen that at an intersection where the cross street is twoway, six turns are possible, two from 13th Street and four into 13th

Street. The diagonal unit blocks are conceptually superimposed. For

clarity, they are shown separately in Figs. 6 and 7. See also Fig. 14. Simple Turn

Appendix H illustrates a simple turn at 13th & Harvard Streets. The numbering of the UBs at the turn is shown. The information

package for the specific turn is reproduced. The general approach to the task is outlined. Turn Bias and Last Chance

Cars are coaxed to get into the correct lane for an approaching

turn by the "turn bias" routine (XL) which causes a car to keep trying

to shift when within 1200 feet of the turn. If, because of continued

congestion, the car cannot shift, it finally reaches a last chance block

beyond which it cannot proceed without shifting lanes. The pattern of last chance blocks is illustrated in Fig. 12. Traffic Signals

Appendix J describes the traffic signal information package and

outlines how the program reads the signal indication and makes a

decision. The traffic signal subroutine (LL2) is generalized. Main

street traffic reads the signal directly; cross street traffic, in effect, reads the same data but draws the opposite conclusion. The signal

timing diagram for the real situation and for the model is shown in Fig. 11. Page 1 of Fig. 11 is the diagram itself, page 2 gives the

13
timing data on which the diagram is based, page 3 explains the diagram

and defines special terms.

Stop Signs

The minor cross streets, Fairmont, Girard and Lamont, are

controlled by stop signs. A car approaching 13th Street from one of these streets will be subject to control by the stop sign routine. A

flow chart for this routine is shown in Appendix M, page 1. First, our

car will be required to come to a complete stop. (When stop is completed, a "1" will be inserted in bit 18. ) Before our car can proceed across the intersection, a check is made of the 20 approaching

UBs on 13th Street for each of the four lanes. If an opposing car is present or moving at all in the nearest UBs our car cannot proceed. If the opposing car is found in UBs farther away, the critical speed is higher. Page 2 of Appendix M shows a table of progressively higher

critical speeds corresponding to the 20 UBs located correspondingly

farther from the intersection. If the speed is exceeded, our car cannot proceed. The critical speeds have been computed on the basis of an

"acceptable gap" of four seconds.

Move Routine

In general the penciled flow charts for the 37 routines have not been reproduced because they are voluminous and would require vast

detailed explanation to be of even dubious value. Reference has already

been made to the stop sign routine (SG2) which, for illustrative purposes, has been reproduced and is explained in Appendix M.

One further example of a flow chart is the move routine (Ml).

(See Appendix N. ) This routine makes the actual move after many

other routines have determined the effective clear distance ahead. If the full clear distance sought has been achieved, the move routine is entered at M2 which accepts and performs the previously determined,

tentative quarter second jump. (Refer again to paragraphs on

Permissible Speed and Sight Distance on pages 11 and 12. ) If the clear

distance has been compromised, the move routine is entered at Ml

which uses the limited clear distance to determine a reduced jump.

In the extreme case, the jump may be zero. The move routine moves the car onto the "B" layout and makes

any appropriate entry in either the Station B or Vehicle Retirement

printout tables (Appendices B and C). If the car is a "marked car", the routine also prints out its quarter second position on a chronological

list. (Refer to Appendix L. ) Additional Details

Appendix K outlines the conditions that must be met when a car makes a turn in the face of opposing traffic. Considerable additional

14
details are available in the appendices, particularly Appendix G on the "Two-Word Format", Appendix F listing the routines, and Appendix O

defining terms.

9. IMPROVEMENTS IN NBS SIMULATION II OVER SIMULATION I Work on NBS Simulation I was stopped in February I960. Some

features were not completed, others were omitted or found defective. The current Simulation II has been completed, improved and expanded

in a number of respects. Below are listed noteworthy items of improvement:

1. Simulation I generated no cross traffic (although cars

turning onto cross streets from 13th Street were carried

away). Simulation II is complete with full handling of both 13th Street and cross street traffic.

2. On the film display of Simulation I, the Irving Street intersection was duplicated in the hope of facilitating observation.

It proved to have the opposite effect. Simulation II eliminates this confusing overlap.

3. In Simulation I cars reaching Monroe Street disappeared

immediately after reaching the center line of Monroe

Street. The new model carries these cars a short distance

beyond the intersection.

4. When the project was started, Irving and Kenyon Streets were two-way streets. Now they are one-way streets. The

revised model incorporates this change.

5. Observation of the Simulation I film indicated a couple of undesirable performance characteristics. At one location,

when cars were stopped at a traffic light succeeding cars disappeared into them. This flaw in the program has been

corrected.

Some cars trapped behind slower leaders bobbed around

excessively trying in vain first one lane and then another in an attempt to overtake. In the revised model, an attempt

has been made to promote greater stability in this situation by not allowing a lane shift unless significant gain in net clear distance ahead can be achieved. This differential was

set at 18 feet whereas formerly a car would shift if it could

gain any advantage at all.

6. The earlier program would search ahead no farther when

finding a leader. The movement of our car would then be

governed solely by the performance of the leader. This

approach was subject to the criticism that a car could "ride on the coat tails" of its leader and thereby go through an

15
amber light or approach an intended turn without slowing

down. The new program makes an independent check

ahead of a leader to assure proper consideration of road

factors that may not be applicable to the leader. This

improvement should improve the realism of the model.

7. In Model I, a car desiring to overtake would always try

the left side first. In Model II, a "coin is tossed" to determine which side is tried first. The second procedure

is thought to be more realistic since 13th Street is operated

one-way with each lane tending to move independently.

8. In Model I, the moving picture was thought to be virtually

the sole end product. It is realized now that means of analyzing the results quantitatively are required. In Model II, the movie is still a valuable, visual guide for judging the performance. but the real output is the series of tables that record volumes and running times. These are discussed elsewhere.

9. In Simulation I, a single word was used to identify a UB. In Simulation II two words are used. The principal addition is the launch time which requires 11 bits. In the first model,

putting all the information into one word was a tight squeeze.

In the revised model there is room for expansion if desired

(additional categories and additional characteristics).

10. Simulation I starts with an empty layout. After three minutes*

the formal run stops, at just about the time the layout is filled with cars. Simulation II is prefaced by an earlier "unofficial" run which has filled the model. The entire 4-minute run of Simulation II displayed in the moving pictures and analyzed in the output tables is based on a full-of-cars model.

11. Simulation I permitted a constant clearance distance between

successive cars. Simulation II provides for an increasing

clearance as speed increases. (See Fig. 15.)

10. ASSUMPTIONS AND PARAMETERS

In many instances, in the absence of specific answers from field data, it was necessary to make certain assumptions or to assign

arbitrary values or distributions to parameters. In most cases these can be readily changed if desired. These assumptions in general relate

to one of two areas: the characteristics of the car or the rules governing the movements. Figure 16 relating to characteristics of vehicles

shows a number of these judgment values. Other arbitrary values and

rules have been used as listed below:

1. Cars generated on 13th Street have been originally distributed

20, 30, 30, 20 per cent across lanes 1, 2, 3 and 4 respectively.

16
2. Cars are launched on 13th Street only if they can be launched

safely at their full desired speed. Generated cars which

cannot be launched immediately are saved until they can be

launched.

3. Cars are launched on cross streets if they can be launched

safely at speeds greater than 15 miles per hour.

4. When a car is considering shifting lanes because of a slow

leader, the car will not abandon its own lane unless it can

gain an advantage of at least 18 feet in net effective sight

distance.

5. Figure 9 shows the volumes assumed at each generation

point.- For the principal streets authentic volumes had

been furnished from field data. For the remainder

arbitrary figures were used. Certain minor movements

were given a token value of 10 cars per hour.

6. Car speeds are reduced to 15 miles per hour for turns. A

moderate deceleration rate of 5 unit points per 1/4 second

per 1/4 second is used, beginning as soon as the car driver "sees" the turn in looking ahead for adequate sight distance.

7. The correct probability distribution that should govern

generation of cars is not known. The available field data

give (in effect) only the mean or "expected value" of this distribution, which is not enough to determine other

important parameters of the distribution (e. g. , its variance).

Although the (binomial) distribution used in the simulation was chosen to have the correct mean value, it may nevertheless distort some aspects of the real situation. If field data to describe completely the distribution were available or were to be gathered, the significant parameters could be

incorporated into the generating mechanism.

17
11. ACKNOWLEDGMENTS

While the final results were due principally to the sustained

effort of the project leader, Martin C. Stark, supporting credit should go to L. Garrett, who wrote the auxiliary program for the oscilloscope

display; L. Cahn, who engineered and operated the special camera

attachment for making the moving pictures; and L. Riches, who

assisted in an important phase of writing the main program. Credit

should also go to John Warme for drawing the figures, Helen Grantham

for typing the manuscript for the final report and Anna K. Smilow for her careful processing of the final copy for publication.

18
SUMMARY OF CARS GENERATED

By Street and by Hourly Rate

Table 1

1 of 2

Cycle Cycle Cycle Total

1 2 3 Period

13th Street 3060 3105 2565 2910

Fairmont Street 90 90 45 75 Girard Street 45 90 90 75

Harvard Street 270 630 90 330

Columbia Road 540 630 630 600

Irving Street 360 360 180 300

Kenyon Street 450 180 90 240

Lamont Street 90 30 Park Road 1035 630 675 780

Monroe Street 135 315 45 165

Note: The signal cycle length is 80 seconds. Cycle 1 represents 320 quarter seconds from simulation- run time 1036 to 1355; cycle 2, from time 1356

to 1675; and cycle 3, from time 1676 to 1995.

1'9
Table 1 2 of 2 SUMMARY OF CARS GENERATED

By Generation Point and by Cycle

Lane 1 Green

Red

Generation

Point

Cycle

1 Cycle

2 Cycle3 Total

13th Street 12

17

2 15 9 412 Lane 2 Green

Red

34

19

1 23 15

2 57

3 Lane 3 Green

Red

56

19 18 16 53 Lane 4 Green

Red

78

10 13 15 38 Fairmont Lane 1 Lane 2 9

10

1

1 2 1 41 Girard Lane 1 Lane 2 11

12 1 2

1

1

14 Harvard Lane 1 Lane 2 1314

3

3 86

11 12

10 Columbia Lane 1 Lane 2 1516 4

8

7

7 8

6

19 21

Irving Lane 1 Lane 2 17

18

355

3

13 911 Kenyon Lane 1 Lane 2

1920

64

13 2 9

7 Lament Lane 2 21 2 2 Park Lane 1 Lane 2 2223

13

10 86 114

3220 Monroe Lane 1 Lane 2 24

25

1234 1 4

7

20
Table 2 SUMMARY OF STATION B COUNTS

Car 8 Passing Station B

Cycle 1 Cycle 2 Cycle 3 Total

Lane 1 Lane 2 Lane 3 Lane 4

20

13

11

18

22

1815

17

23

24

21

20

65

5547

55

62 72 88 222

Hourly- rate 2790 3240 3960 3330

Notes: Station B is located on 13th Street just north of Lament Street. Cycle 1 is from simulation- run time 1036

to 1355; cycle 2, from time 1356 to 1675; and cycle 3, from time 1676 to 1995.

21
Table 3 SUMMARY OF VEHICLE RETIREMENT DATA

(Volumes and Running Times)

Cars Retiring at End of 13th Street Cycle 1 Cycle 2 Cycle 3 Total

Lane 1 Lane 2 Lane 3 Lane 4

4

6

11

11

20

16

17

17

1113

17

17

3535

45

45

32 70 58 160 Hourly rate 1440 3150 2610 2400

Distribution of Running Times

(Of Cars Traversing Entire 13th Street Course)

Running Times

(in 1/4 sec.

)

Cycle 1 Cycle 2 Cycle 3 Total

200-249

250-299 4 4 300-349 3 3 2 8 350-399 12 12 15 39 400-449 2 23 9 34

450-499 3 9 7 19 500-549 7 5 12 550-599 4 11 15 600-649 2 2 4 650-699

Total cars 24 60 51 135 Average running

time 365 444 464 437

22
TL SIGNALS

M STOP SIGNS —»» ONE WAY

LA MO NT ST.

IRVING ST.

i=— COLUMBIA RD.

HARVARD ST.

GIRARO ST.

FAIRMONT ST.

TL EUCLID ST.

FIGURE I. I3TH STREET LAYOUT

23
#Wg) •«** $k© **

COLUMBIA

CIRCLED FIGURES ARE

GENERATION POINTS. ATTACHED ARROW SHOWS

UNIT BLOCK FED BY GENERATION POINT.

FOR SIMPLICITY, DIAGRAM SHOWS THE NUMBERING OF ONLY THE FIRST AND LAST THREE UNIT BLOCKS OF EACH LANE.

FIGURE 2. GENERATION POINTS AND UNIT BLOCK NUMBERING

24
STATION B CHECKPOINT

©

©

©

©

©

©

®/ ©

;#-

>*

©

© LAMONT

KENYON

(?) IRVING

COLUMBIA © HARVARD @ 6IRARD

FAIRMONT

EUCLID FIGURE 3. EXIT NUMBERS AND STATION B CHECK POINT

25
JL

JLro

«*- COLUMBIA

HARVARD

6IRARD

FAIRMONT

EUCLID

START

HERE

END HEREl< 4#

<*V*

-y\\

LAMONT

KENYON

IRVING

RESUME

HERE

FIGURE 4. I3TH STREET AS SHOWN ON OSCILLOSCOPE

26
HVO Q1WH

fr 3NV1 H3J3Hd *

PS

AM091LV0 033dS

Q3HIS3Q

Q33dS J ivniov

11X3 i

NOlllSOd 31GQVH1S

3H3HM m

mwm\

S3lllMVin93MMI SnOIHVA

a Noiivis

roesicjco

}

Q3dd01S SVH

3dAl

CO UJZqS_ LU CDUJHCO

3HI1 HONnVl

8-1 31V9

27
1916 1316 716 116 GiRARD ST.

10

CNJ

CO

i

CNJ o1

LO

CNJ CO

lo ^s^ CNJ \^ LO lo

CNJ loCsJ ro

c»

cn

ro \^v

c=> 7* ro

*cn

3314 —

1910 1310 710 \fo ^— 3312 fero

1908 1308 708 108 LANE 4 3 2 1

FIGURE 6. TURNS FROM I3TH STREET INTO GIRARD STREET

IBI6 J^ie"

3320

716 •u" y— 3316

6IRARD ST. w V

oCO

LO

cnj

**- r— N^><=>

CNJ oo

CO

lO

CNJ CNJ ro

cnoo ro/ ro

cnro

-4> A

INcr

IN. ro

cnCM /" \

3322-7\_-

Aco 1910 1310 710 110 ^—3318

1908 1308 708 108 LANE 4 3 2 1

FIGURE 7. TURNS FROM GIRARD STREET INTO I3TH STREET

28
0552 2548

—ro

ro J

2SQ2

2546

fr5S2 2544

9992

2542

2540 9&2

2538 2992 2536

t?992 2534 9952

2532

9952

2530 0iS2 ~ ~ s s

CO = ^ <x

/ oo a S

«3- £ a s X x> s ft s

\ Si s

s = a § !524 o 1 1

<f

Si

22 a

2 s H I'' £V 1 1 I

^*r

OJ

ro

ro -\

2520 - IS Hl£l i

0852

2518 2852

2516

fr8S2 2514 3C 1 9852 2512

8852

0652 i 2652 2506

t>652 2504

9652

8652 m

29
ENTRANCE VOLUMES

ARE SHOWN ON CROSS STREETS

*W

*K*

$&

20 LAMONT

269 KENYON

IRVING

668 COLUMBIA

HARVARD

50 GIRARD

50 FAIRMONT

EUCLID FIGURE 9. DESIGN VOLUMES

50
2 of 2

Entrance

Street and Lane

Hourly

Rate

13th Lane 12

34

610

915

915

610

Fairmont e/b

w/b

5050 Girard e/b

w/b

50

50 Harvard E/B (So.)

E/B (No.)

354

354

Columbia W/B (So.)

W/B (No.)

334

334

Irving E/B (So.)

E/B (No.)

184 184 Kenyon W/B (So.)

W/B (No. ) 135 134 Lament w/b 20 Park e/b

w/b

366

304

Monroe e/b

w/b

75

75

Probability

Value (A)

4.24

6.36

6.36

4.24

.35

.35

.35

.35

2.46

2.46

2.32

2.32

1.28

1.28

.94

.93

. 14 2.54

2. 11 .52

.52 Note A Percent of time car should be generated per quarter

second. Every quarter second, each probability value

is compared with a newly generated random number in the range 0. to 99. 99. If random number is less than probability value, a car is generated at the entrance

indicated.

Fig. 9. Summary of Design Volumes for Entrance Into Model

31
m

f Hi

p) v

H

V

P WOULD REQUIRE CLEAR

SI6HT DISTANCE TO HERE

WOULD LIKE TO HAKE

1/4 SEC. JUMP TO HERE

; NOSE OF OUR CAR

LL L A R RR

A

RRR

LLL

LANE DESIGNATIONS: OUR LANE

RI6HT LANE

DOUBLE RIGHT LANE

LEFT LANE

DOUBLE LEFT LANE

FIGURE 10. THE BASIC FORWARD MOVE

32
S s

33
2 of 3

Seconds Begin

Absc

13th Green

13th 13th lute Scale

Offset Green

50

A Red A

30

(1/4 sec.)

B

Euclid

Harvard 28 55 25 112 Columbia 36 50 3X) 144

Irving 45 50 30 180 Kenyon 55 50 30 220

Park 70 50 30 280

Monroe 75 55 25 300

Notes:A - Splits shown include 4- second amber

B - Simulation clock goes from to 319 quarter seconds and repeats,

Basic data taken from records of District of Columbia Department

of Highways and Traffic April 9, 1959.

Fig. 11. Signal Timing Data for 1 3th Street

34
3 of 3 Fig. 11. SIGNAL TIMING DATA FOR 13TH STREET

Explanation of diagram on. page 1: Green on the main street is indicated by the absence of any marking. Red is indicated by the cross-hatched areas. Amber (at the end of 13th Street green) is indicated by an open outline. The cycle length is 80 seconds (or 320 quarter seconds). The diagram shows several (repeating)

cycles.

The broad open bands progressing diagonally up the page

represent the bands of traffic which can progress up the street in unison with the (green) timing of the traffic signals. The signals on this section of 13th Street are set for a smooth flow of 26. 8 mph

in the P. M. rush period.

Definitions:

Split: The apportionment of the total cycle to different signal

indications.

Offset: The means of defining the linkage of signal indications at interconnected signalized intersections. The beginning of green on the main street is taken as the point of reference.

In the table on page 2, Euclid Street, with a offset, is used as the datum location. The 28-second offset shown for Harvard Street, for example, means that 13th Street green

begins at Harvard Street 28 seconds later than it begins at Euclid Street.

35
LEFT TURN

LANE 3 LAST CHANCE TO SHIFT LEFT

IS AT UB 1640

LANE 2 LAST CHANCE TO SHIFT LEFT

IS AT UB 1014 *

LANE I LAST CHANCE TO SHIFT LEFT

IS AT UB 400

LANE

2226

2214

2200

\

1626 /

1614

1600

/

1026

1014 \

1000

426

414

400 \

IS AT UB 458

LANE 2 LAST CHANCE TO SHIFT RIGHT

IS AT UB 1040

LANE 3 LAST CHANCE TO SHIFT RIGHT

IS AT UB 1626 *

LANE 4 LAST CHANCE TO SHIFT RI6HT

IS AT UB 2200

•3jfr NECESSARILY OFFSET FROM ITS COUNTERPART TO AVOID THE

POSSIBILITY OF A STALEMATE .

FIGURE 12. PATTERN OF LAST CHANCE UNIT BLOCKS

36
Time Car 1 Car 2 Car 3 Time Car 1 Car 2 Car 3

1 2502 2510 2560 26 2520 1916 2576

2 2504 2512 2562 27 2520 1918 2578

3 2506 2514 2564 28 2522 1918 2578

4 2508 2516 2566 29 2522 1920 2580

5 2508 2516 2566 30 2522 1920 2580

6 2510 2518 2568 31 2522 1922 2582

7 2512 2518 2568 32 2524 1924 2582

8 2514 2518 2568 33 2524 1924 2S84

9 2514 2518 2568 34 3318 1926 2586

10 2514 2518 2568 35 3318 1928 2586

11 2516 2518 2568 36 112 1928 2588

12 2516 2520 2570 37 112 1930 2590

13 2516 2520 2570 38 114 1932 2590

14 2518 2520 2570 39 114 1934 2592

15 2518 2520 2570 40 116 1936 2594

16 2518 3322 2570 41 116 1938 2596

17 2518 3322 2570 42 118 1940 2598

18 2518 3322 2572 43 120 1942

19 2518 3322 2572 44 120 1944

20 2518 1912 2572 45 122 1946

21 2520 1912 2572 46 124 1948

22 2520 1912 2574 47 126 1950

23 2520 1914 2574 48 128 1952 24 2520 1914 2574 49 130 1954

25 2520 1916 2576 50 130 1956

Fig. 13. Table of Successive Car Positions in Left-Turn Exercise

(Quarter Seconds and Unit Blocks Occupied)

37
Fig. /«4 Unit Block Turn Sequences at 13th & Girard Streets

Uight from Lane 1 Left from Lane 4 Right into Lane 1 Right into Lane 4

Left into Lane 1

Left into Lane 4

108-110-3312-2528-2530

1908-1910-1912-3314-2578-2580

2568-2570-3316-114-116

2568-2570-2572-2574-2576-3320-

1914-1916

2518-2520-2522-2524-2526-3318-

' 112-114-116

2518-2520-3322-1912-1914-1916

Fig. 14. Unit Block Turn Sequences at 13th and Girard Streets
QuarterM. P. Ho Second

Jump

Stopping

Distance Clearance

Goal

Points

40 390

2 1/2 8 8 60 418

5 15 15 80 445

7 1/2 23 26 100 476

10 31 48 120 518

12 1/2 38 72 140 562

15 46 106 160 616

17 1/2 53 140 180 670

20 61 186 200 736

22 1/2 69 238 220 808

25 76 289 240 879

27 1/2 84 353 260 963

30 92 423 280 1053

32 1/2 99 490 300 1140

35 107 573 320 1243

Distances are in unit points (100 unit points = 12 feet)

Goal points = stopping distance + clearance + 350 (maximum

possible length of leader)

Fig. 15. Jump-Stopping Distance -Goal Points Table

39
Fig. |6 Characteristics by Type of Vehicle

Desired

Speed Passenger

Car

Truck

A

Truck

Category V[. P.H.

35 B

15%

1 30 35 20% 15%

2 25 35 60 35

3 20 15 20 35

4 15 15

Length (feet) 18 30 42 Acceleration ( anit points 3 2 2 per 1/4 sec. per l/4 sec.)

Deceleration (unit points 10 per 1/4 sec. per 1/4 sec.)

10 10

Type of Vehicle by Street

Passenger car Truck A

Truck B

13th Street 99.0%

0.5

0.5

Irving

Kenyon

92.0%

4.0

4.0

Park

97.0%

1.5

1.5

All Other

99. 0%

0.5

0.5

Fig. 16. Characteristics by Type of Vehicle

Ja
When

InU

Cannot

Enter

W

X

W + 1

Condition

If any car in X

If any car in Y + 2

If any car in Y + 1 If any car in Y

If any car in Y - 1 moving >

If any car in Y - 2 moving > 10

If any car in Y - 3 moving > 20

If any car in Y - 4 moving > 30

If any car in X

If any car in V moving >

If any car in W

No restriction Note: Stated speeds are in unit points per quarter second.

Fig. 17 Conditions for Conflicting Turn

41
J O O ro -* 00 H (M CO | lf> | CO CO CO i CO g CO CO CO CO

«tf NO o o

CO -^

CO CO

oi

00 o ^ 00 o fsl «* o eg 1 *• 1 o 00 o^ o

CO CO 1 ^ CO CO CO ^

CO CO CO ' CO CO CO CO

J o

•sD 00 o «* O rg O H CO 1 *ft 1 1 O O

CO CO CO ^ CO Tf

CO CO CO CO CO CO

aD

co

3

^ >£> o «* vO 00 o

o r-H

1 <* 1 >a r^ 00 o CO CO CO CO CO co ^

CO CO co CO CO CO CO

0)a

4-> cd

o

u

CvJ •* oo fM sO 00 o —

i <*> 1 ^> 1 oo o co CO CO CO CO CO

en CO ' CO CO ' CO CO

3 J o (M ^ 00 pg -* •vO o i—

<\J 1 "* i r- oo o CO CO CO « 1 CO CO CO

CO CO CO CO CO CO CO

1 1

T3

ffi 3 fi S

42
VEHICLf GENFRATI

SP CAT , GEN MARKED LANE PREF APPENDIX A

I OF 7

VEHICLE GENERATION TABLF

MARKED LANE PREF

1094 1097

1098 o 1100 1 1101 13 1103 10 1104

1107 1U7 13 1117 13 1119 1119 10 1126 .»* 1127

1132 6 1135 12 1138 1142 o 1144 10 1145 11 1148

1149 13 _ _ 1151

1153 o

. 1154 13 1156

1160

1162 5
VFHICLF GFNFRAT10N TABLF

VEH1CLF GENERATI

APPENDIX A

2 OF 7
VFHICLF GENERATI APPENDIX

3 OF 7

VEHICLE GENERATION TABLE
APPENDIX A

4 OF 7

1476 5 1477

1*86 7 1494 7 1503 13 1506 6 1519 13 1520 10 1522 6 1524 7 1526 6 1549

1552 14 1561 6 1562 1 1566 14

1585 12 1587 12 1589 4 1590

1594 6 1600 1600

1600

1603

13
VEHICLE GENERATION TABLE

1606 1607

1620 5 1620 1 _!*?*_ ; 5 1625 6 1627

1628 5 1629 5 1630

1630 10 1632

1633 5 1633 1635

1637 5 1638

163' 6 1639 6 16*0

1644

1645

1648 1650

1662

1666

1666

1666

1667 1669

1670

1683

MARKED LANE PREF

VEHICLE GENERATION TABLE

LANE PREF

1697

1704
VEHICLF GENERATION TABLE

GEN PT TY

1730

173*.

moo

i«oa

VEHICLE GENERATION TABLE

LANE PREF

1826 1R32

I
VEHICLE GENERATION TABLE

SP CAT GEN TYPE MARKED LANE PREF APPENDIX A

7 OF 7

VEHICLE GENERATION TABLE_

TYPE MARKED

STATION Fl CHECK

1 LANF APPENDIX B

I OF 4

1047

1052

1225

1230

1235

1236

1239

1241 1253

1258

125fl J2 59 1263

1268 1268

1269

1271

STATION B CHECK

TIME

1276
APPENDIX B

2 OF 4

STATION B CHECK

1156

1321
STATION B CHECK APPENDIX B

3 OF 4

1632

1637 1637

1652 128 2 1658 1659 1302

1659

1665 1666 16701324

1671

1679 1684

1685 1333

1685

1692 1339

1706

1708

1711

_1_7_14 1716 1719

STATION B CHECK

1747 1753
STATION R CHECK

B93 15)9

917 1600

922 1650

ANE 2 LANE 3 LANE

93* 1692

APPENDIX B 4 OF 4

STATION R CHFCK

LANE 1 LANE 2
1CLF RFTIRFMFNT APPENDIX C

I OF 3

1059 1076

1 3 13 1,13

VEHICLE RETIREMENT TABLE

LAUNCH TIME

1 3 75

1 3 78 I386

1392

1398 U02
VEHICLE RET

?EtIRE TIME APPENDIX C

2 OF 3

H54

1455 U56 463 H58 398 1460 333

1465 379 H75 401 UBO 473

1480 410

VEHICLE RETIREMENT

RETIRE TIME

1639

1642

1661 1661
VEHICLF RFTIRFMFNT

LANE EXIT APPENDIX C

RETIRE TIME RUN TIME 3 OF 3

1714 335 1720

1731

393 394

1736 395 439

1770 413

1776 420

1776 491 . ... . ......__ 1782 43 2 1787 494

1793 467

1794 461 1798 402

1799 431

1801 462

1805 404

1806 399 1806 418

1811 413

1811 380 1815 48 3 1828

1835 1925 478

1925

1929

'

. 1941 500

VEHICLE RETIREMENT TABLE

RETIRE TIME RUN TIME

1948 587

1958 539

570 1959 643

1963 603

1965 574

1968 540

.1971 567

1973 591 1976 566 1977 571 1980 583

1981 553 524

1985 576

1985 377

1987 547 1987 rro 1990 360 1992

203 456 520 928 940

204 456 520 930 942

456 520 932

'.56 520 940 958

o APPENDIX D

n I OF 8

946 968 2

221 456 520 950 222 456 952 974

456 520 958

226 456 520 960 986 2 229 456 520 960 988 2 962 990 2 520 962 992

456 520

520 968 998 520 968

243 456

244 456

262 520

2200 2202
OAPPENOIX D

o 2 OF 8
1082 i i 1084 88 1084 19 SO 1086 12

1088 h

1090 !9 >6 1090 >8 1092 2C 00 1094 2C 02

1096 20 04 1096 2(

2(

06

06 1100 2.C 08 1100 2( 10

110? 2( 12 1102 2(

21

12

1106 2( 16 1106 2( 16 1108 2( 16 1110 2( 16 1110 2( 16 1112 2< 16 1112 2( 16 1114 2C 16 1116 20 16 1116 20 16 1118 20 16 1118 20 6

1122 1122 2( 16

1124

2< 16 1126 21 16 1128 21 16 1128

2|

16

1132 20 6 1132 20 6 1134 1134 20 6 1136 20 6 1138 20 .6 1138 20 16 1140 20 16 1140 2J>U

2248 2250

225 2 2252

2256 2794

2256 2796

2256 2796

2258 2798

3386 28 20

2822

282 2

2 2968

2 2968

2 2968

2 2968

Z 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968 2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2968

2 2969

2 2968

2912 2968 31

16 2912 2968 31

16 2912 2970 31

.6 2912 2970 3 1 16 2912 2970 31 2912 2970 31

.6 2912 2970 31

16 2=12 2970 31

16 2912 2970 31

16 291? 2=72 31

6 29,2 2972 31

16 2912 2972 31

16 2912 2072 31

.6 2912 2974 31

16 2912 2974 31

2968

3168

2818 2912

2912 2968 31

?912 2968

3131 2912 2912

2968

2968 2968 3168

31

31

^APPENDIX d

. 3 OF 8

2968 3 2968 3 2968 3

3
2918 2982

1*29 20* 20L6

i APPENDIX D

, 4 OF 8

ooo

224 2T22

226 21-2* 31

230 2026 3172

32 2028 3172

0_ __0

.0

1*66 8*2
858 20.8 3

67 862

68 864

474 876

475 878

476 880

486 898

492 908

502 326

503 326

oAPPENDIX

„ 5 OF 8
1535 1536

1545 358

1559 378

"APPENDIX D

o 6 OF 8

1565 388
1586 4 2 a APPENDIX D

. 7 0F8

456 22 70 458 22 '0 460 22 2.

22 '8 22 78

472 22 14 472 2294 474 22B6 476 22 478 2;9 480

484 2; 94

492 231 494 23(4 496 230 5

506 23 18 508 23C0

508 23B2
16*9 510 22 24 1650 510 23 24 1651 512 2: 26 __.°-_

1652 514 2: 28 o 1653 514 2 30 1654 516 2 30 1655 516 2: 32 • 1656 518 2: 34 1657 5-20 2: 36

1658 520 23 36 o 1659 522 23 38 1660 524 23 40 1661 1662

1663

1664

1665 1666^

1667

'APPENDIX D

, 8 OF 8

o o o o o o o o o o o o oo_o ooo

1670

1671

1 672

1673

1674

1675 1676

1677

1678

1679 1680

16B4

1685 1686 1687

1690

1691 1692

1693

1695

1696

1697 1698 •

1706

1707
Appendix E

THE BASIC FORWARD MOVE

(Refer to Fig. 10) Ours is vehicle B. After considering our present speed (last jump) and acceleration rate, it is determined we may hope to jump as

far as N. We must, however, have an adequate clear (sight) distance

ahead. For a first try, if we can probe ahead unit block by unit block

and find no car as far as P, a distance taken from a table, we may

proceed to jump to N as desired, without further ado. Suppose however, we find an obstacle in car C. We now do a "second approximation" which takes into consideration the length of leader C, the leader's speed and the required clearance at that speed.

A new comparison is made. If C is going fast enough, the "credit" for C's momentum will still give us an effective clear distance to P and we can move to N as desired. Let us assume that the revised sight distance is still less than P. Now we "toss a coin" to determine on which side we will try first to overtake (on this 1-way street). Suppose we will try left first. We

will probe behind us a sufficient distance in the L lane to determine

whether we can pull out safely. Then we will probe forward in the L

lane in the same manner as we did in the A lane. We will also check

the LL lane to make sure someone in that lane is not also attempting

to shift into the L lane. When our check of the L lane is completed, we will proceed to

shift into the L, lane if our effective clear distance achieves P. Otherwise we will try the R lane. Ultimately we may have to compare

the effective clear distances in the L, A and R lane tries. We will select the best. To the extent that our best effective clear distance is

still less than the desired P, we will scale down our actual jump to a

point short of N. The general case involves five lanes. Actually, 13th Street has

only four lanes. Before testing a side lane, a test is made to ensure

that such a lane exists. Superimposed on the basic maneuver described in the preceding

paragraphs is a constant check to see whether any unit block is irregular. The "irregular routine" will take over to do the necessary

in case a significant irregularity is encountered. The irregularities

have been described elsewhere and include such items as the following:

traffic lights, turns, check points, cross flow.

67
Appendix F

1 of 3 LIST OF ROUTINES

SQ4

L2

B7

XL

Sequence Control. Handles the order of the principal

routines.

Generation. Generates cars, including their characteristics

at 25 gates and launches them.

13th Street Master Routine. Searches for a car on 13th Street and supervises the processing of it. Turn Bias. Checks each 13th Street car to see if "turn

bias" is in effect. (If car is within 100 UBs of an intended

turn, it must try continually to shift into correct lane for

turn.

)

C2 Lane Control. Supervises the trying and selection of the "A", "R" and "L" lanes. TA1 Try "A" Lane. Subroutine for trying to achieve goal points

in "A" lane of 13th Street. TL1 Try "L" Lane. Subroutine for trying to achieve goal points

to overtake on left. TR1 Try "R" Lane. Subroutine for trying to achieve goal points

to overtake on right.

ST2 Straddle. If car is in "straddle" position, this subroutine

continues the lane switch already started. D2 13th Street Diagonal Routine. Main routine for processing

cars found half way around turns off 13th Street. XT1 Cross Street Master Routine. Main routine for processing

traffic on nine cross streets. TY2 Cross Traffic Turn. Supervises right turns and un- opposed left turns from cross streets. LTU2 Left Turn. Starts the left turn from cross street when

subject to opposing traffic. XD2 Cross Street Diagonal Routine. Main routine for processing

cars found halfway around turns off cross streets. LTV2 Left Turn Diagonal Routine. Diagonal routine for completing left turn in face of opposing traffic. 68
Appendix F

2 of 3 Ml 13th Street Move. Subroutine for using previously

determined clear distance and making actual move for

13th Street car. DM1 13th Street Diagonal Move. Subroutine for using previously

determined clear distance and making actual move when car

is found in diagonal block turning off 13th Street. XM1 Cross Street Move. Subroutine for using previously

determined clear distance and making actual move for cross

traffic. XDMl Cross Street Diagonal Move. Subroutine for using previously

determined clear distance and making actual move when car

is found in diagonal block turning off cross street. IR2 Irregular. Generalized master subroutine for handling

"irregularities" on both 13th Street and cross streets

(traffic signal, cross flow, turn, end block, etc.).

F6 13th Street Cross Flow. Subroutine under IR2 applicable to 13th Street traffic for testing for road block by cross traffic. KF2 Cross Street Cross Flow. Subroutine (under IR2) applicable

to cross street traffic for testing for road block by 13th Street traffic. K3

LL2

SG2

LCI

13th Street Turn.

13th Street. Subroutine for heading into a turn off

Traffic Light. Generalized subroutine to evaluate traffic signal indication.. Stop Sign. Requires cross-street car to stop and then

checks main street for sufficient gap to proceed. Last Chance. Subroutine for imposing last chance

restriction (on 13th Street cars intending to turn).

TLT1 Traffic Light and Turn Special Routine. Checks for

significant irregularities independent of car ahead (on

13th Street).

XTLT1 Traffic Light and Turn Special Routine for Cross Traffic. Checks for significant irregularities independent of car ahead (on cross street).

2PX2 2nd Approximation. Subroutine for rechecking effective clear distance ahead in light of speed and length of leader

and clearance at particular speed.

69
Appendix F

3 of 3 GP2 Goal Points. Subroutine which considers present speed,

desired speed and allowable acceleration and sets up goal

points (clear distance ahead) needed to permit desired move.

SSI Stopping Distance. Subroutine for computing stopping

distance from jump.

SL1 Slow. Subroutine for slowing cars to 15 m. p. h. for turns. CLC1 Clearance. Subroutine for selecting the proper clearance

for a particular speed.

SB 1 Backward Goal Points. Subroutine for computing required

clear distance behind, in adjacent lane, to permit pulling out of lane to overtake.

SA1 Backward Stopping Distance Adjustment. Subroutine for determining own stopping distance and applying it in computation of "backward goal points. " P2 Preparation. One-time routine for (1) spotting bits in appropriate UBs to identify irregularities (traffic light, turn, end block, etc.) and (2) adjusting the vehicle probability figures to conform with a binary number system.

EDIT Edit. Assigns coordinates to car and signal positions and

writes the information on magnetic tape to be used later by

SEAC for plotting points on oscilloscope display.

70
Appendix G

1 of 3 THE TWO-WORD FORMAT

(Refer to Fig. 5) Two words of information are assigned to each UB. The first word and the first part of the second word describe the characteristics

of a car, if there is one in the UB. The last part of the second word

describes the roadway at that point by noting the presence of one or more "irregularities", if any exist. When a significant irregularity

is noted, the program is alerted to go to a table stored in memory

where the necessary, detailed additional information is on file for

that UB.

As the car moves, all the information describing the car is "lifted" and is transferred to the new UB to which the car progresses.

The information in the last part of word 2 describing the roadway is stationary. It is masked and remains always with the UB to which it refers.There follows a basic explanation of the information content of the bits in the two words used to describe the car and the roadway:

P-bit in word 1: A bit here, where it can be easily checked,

indicates that the UB contains (the nose of a) car.

Bits 1 to 7: These indicate the exact position of the car within

the UB in terms of unit points (100 unit points = 12 feet). Bits 8 to 10: A non-zero straddle position means that the car is in the process of shifting lanes. Values of 1, 2 or 3 indicate

progressive intermediate positions in a right shift. Values of 5, 6 or

7 indicate progressive intermediate positions in a left shift. Bits 12 to 15: Sixteen exits (or destinations) are possible. For

convenience, exit is straight out 13th Street, odd non-zero exits are

to the right and even non-zero exits are to the left. Bits 18 to 24: Actual or present speed is shown here by the "last jump" expressed in terms of unit points per quarter second.

Bits 25 to 28: Desired speed is shown by category. The format

allows for 16 categories. Actually only 5 are presently used

(corresponding to 35, 30, 25, 20 and 15 m. p. h.). The program refers

to a table to find the speed corresponding to the category number.

Bit 34: A bit here indicates a preference for lane 4. This has

meaning only to cross traffic turning into 13th Street where the turning car is destined straight out 13th Street and has no real preference

between lane 1 or lane 4. At the time of generation a bit is entered

here, or not, on a random basis.

71
Appendix G

2 of 3 Bit 35: A bit here indicates that this is a "marked car". The

computer printout sheets have provision for tracing the quarter -second

movements of a small number of cars. These cars are the so-called

"marked cars" and cannot at any one time exceed 18, which is the number of columns on the printout sheet. It should be clear that this device in no way limits the number of cars simulated, or treated in the sumr.iary tables and in the moving picture. It is useful for sampling

car performance and for recording detailed movements of specific cars

as an aid in debugging or analyzing a special situation. P-bit in word 2: A bit here indicates that the car originated at the base of 13th Street. Running times are computed only for those cars which traverse the entire 13th Street course.

Bits 1 to 11: The launch time is the time when the car enters the model. Expressed in quarter seconds, it is nearly always specific to a single car and thus serves to identify the car so that the specific car can be spotted as it passes later check points. Bits 12 to 14: These three bits can identify eight possible vehicle

types. At present only three are used: passenger car, truck A and

truck B. The program will refer to a table to find the vehicle length

and acceleration rate applicable to each type. Bit 18: A bit here indicates that the car has stopped at a stop

sign. The stop sign routine will not clear a car for proceeding until

it has stopped.

Bit 24: A bit here tells the program that this UB is the Station B

check point. Bit 35: A bit here is the general alert for an irregularity in the UB. The program must then check in detail through bits 27 to 34

(shown below) to determine the specific irregularity or irregularities

applicable to the UB in question.

Bit 27, left turn: A bit here calls the routine which will guide car into left turn in the face of opposing traffic (necessarily cross

traffic in this model because 13th Street is one-way).

Bit 28, stop sign: The stop sign routine will perform here.

Bit 29, last chance: A car cannot go past this point without

shifting lanes, to be in the correct lane for an intended turn. If necessary a car will actually halt in a last-chance UB until it can shift

to the next lane. However, this seldom happens because for 100 UBs

(1200 feet) in advance of an intersection an intending turner will keep

"trying" to get into the correct lane for the turn and usually succeeds.

72
Appendix G

3 of 3 Bit 30, cross flow: The program will check all UBs in the intersection crossing the path of the car being processed, for a possible

road block.

Bit 31, turn: This indicates an unopposed, simple turn as distinguished from the "left turn under conflict" (bit 27). Bit 32, traffic light: The traffic light routine will read the signal

indication and control the car accordingly.

Bit 33, end: The last UB in each lane is marked as an "end

block". A car reaching this point is "in the clear" and can be retired. Also, the program is alerted to set up for searching the next lane. Bit 34, beginning: For purposes of stabilizing the send-off, no

lane shifting is permitted in the first 10 UBs of the four 13th Street

lane s

73
ILLUSTRATION OF A SIMPLE TURN

Appendix H

1 of 2

POINT OF TANGENCY

HARVARD ST. LANE 2 EXIT 5

POINT OF CURVATURE J |;5

"t

When car reaches UB 2670, the program seeks out an "information

package" filed for turn block 2670. The package is shown at the left below, with a brief explanation of each item:

2670 - The turn block which identifies the package.

5 - The straight-through exit. 54 - The location of point of curvature (unit points).

3334 - The identity of the diagonal block. 1970 - The identity of the tangent block. 21 - The location of point of tangency (unit points). 4 - Turn is into lane 4_ of 13th Street.

- No opposing lane.

74
Appendix H

2 of 2 In making the turn the car would progress through UBs 2666-

2668-2670-3334-1970-1972. When the program has searched out the special information package for UB 2670, it will first check the exit

of our car. If it is not "5", our car is interested in turning into 13th Street. Further checks are made to determine whether we should

turn into lane 4 or lane 1 of 13th Street. If lane 4 is desired, the information package provides the necessary information regarding

the movement from one UB to the next. The package also notes (in item 8) that there is no opposing lane to hamper the turn (that is, turn is from a one-way street). Had there been an opposing lane a more complicated routine would be used which would identify and

check the opposing UBs.

75
Appendix I

1 of 2 LEFT TURN EXERCISE

Three cars were planted on Girard Street. A diagram (Fig- 8) shows the numbering of the 12 -foot unit blocks involved in turning left from Girard Street into 13th Street. The numbering steps by two

(because of two-word information packages for each unit block). It may be noted that each of the four lanes on 13th Street is progressively

numbered and differs from adjacent lanes by 600. The unit block numbering on the cross streets also follows a simple system. The eastbound lane of Girard Street starts at unit block 2500 and progresses 2502, 2504, . . „ up to 2548. The westbound

lane is numbered 50 higher, starting at 2550 and progressing (by twos)

to 2598. The two diagonal blocks 3322 and 3318 are special blocks out

of sequence which serve as transition links between the Girard Street series and the 13th Street series for those cars making left turns into lane 4 and lane 1, respectively, of 13th Street. The three cars were planted as follows: (nose of) car 1 in unit block 2502 desiring to make a left turn, car 2 in UB 2510 also desiring

to turn left and car 3 in UB 2 560 symmetrically opposed to car 2 intending however to go straight.

Let us turn our attention to Fig. 13 which traces through the movement of these three cars. The data have been extracted directly

from a computer printout sheet showing how the simulation program

processed the cars. The first column represents time in terms of quarter seconds. In the second column the successive positions of car 1 are followed through. Similarly columns 3 and 4 describe the movement of cars 2 and 3. At the start each car is moving at a speed of about 30 mph (the assigned "desired" speed) and thus traverses about one 12-foot unit block each quarter second. The computer retains the exact position of each car within the unit block although the printout shows only the identity of the UB. Thus if the printout shows a car spending two time

intervals in the same UB, conceptually the car is in the tail of the UB

in the first interval and at the head of it in the second interval. The movement of the three cars can be visualized by reference

to the diagram simultaneously with noting in what UB each car is after each quarter second. Comments on the vehicle behaviors are

given below referenced to the applicable time interval: Time 4: The cars are beginning to slow up because of Stop

signs in UBs 2518 and 2568.

76
Appendix I 2 of 2 Time 10:Cars 2 and 3 are coming to a complete stop at the Stop

signs. Car 1 is crawling. An incidental note is that

to this point the behavior of cars 2 and 3 has been

exactly symmetrical.

Time 12: Having completed their stops, cars 2 and 3 now

proceed because no traffic was found on 13th Street. Time 16:Car 2 quickly swings into its turn (diagonal UB 3322)

before car 3 becomes a hazard.

Time 20: Car 2 completes its turn into lane 4 of 13th Street (UBs in 1900 series).

Time 22: Car 1 is moving up and would like to make the same

turn but car 3 is too close. Time 25: Car 1 will give up its aspiration to turn into lane 4, will settle for lane 1. The rules governing this situation are described in the paragraphs entitled "Turns" and "Lane Preference" in Chapter 8. Time 34: Car 1 now turns into lane 1. Had there been opposition, car 1 would have waited until it could turn. Time 42: Car 3 reaches the last UB on Girard Street and retires

from the display. Note that car 2 has resumed its desired speed and that car 1 is rapidly picking up speed having completed its turn into lane 1 (UBs in 100

series).

77
Appendix J TRAFFIC SIGNAL PACKAGE

The information package for a traffic signal UB is shown at the

left below, with explanations:

272 - Irving Street traffic light UB

30 - Unit point location of stop line 44 - End of green alone on 13th (quarter sec.

)

60 - End of green-amber on 13th 164 - End of green alone on cross street

180 - End of green-amber on cross street When the irregularity for a traffic signal is noted, the program

first finds the information package (like the above) relating to the UB

in question (272 in the example). The clock (0 to 319) is consulted to determine whether signal is green, red or amber. If it is green, the

effect is as though there were no signal, and control is returned to the main scan routine which will continue to check successive UBs in attempting to achieve a required clear (sight) distance ahead. If signal

is red, the confirmed points from car to stop line are determined,

and the car will prepare to stop accordingly. If signal is amber, car's stopping distance is computed (from a look-up table). If car can stop,

it will. Otherwise it will "run" the amber light.

The same information package is used for all four 13th Street lanes by utilizing the "modulo 600" feature of the numbering of the 13th Street lanes. Thus when the traffic signal UB in lane 1 is 272, in lane 2 it is 872,' in lane 3, 1472 and in lane 4, 2072. Cross traffic also uses the same information package through reference to a cross index

which notes that for Irving Street traffic signal UB 2718, the program

should refer to the data for UB 272 (with green and red indications

properly reversed, of course).

The timing of the signal can be easily modified by merely

changirg the values in the information package, once the desired

offsets have been calculated referenced to the Euclid Street zero

point and expressed in quarter seconds.

78
Appendix K

CONDITIONS FOR CONFLICTING TURN

The diagram and table of conditions (See Fig. 17) indicate the general procedure involved in moving a car into a turn when there

may be opposing traffic that will block or interfere with the movement

of our car.

In the diagram, three lanes are depicted at an intersection: an

eastbound lane, westbound and northbound. A car turning from east- bound to northbound must cross the westbound through lane as well

as avoid any car turning from westbound to northbound. Also, a car

turning from westbound to northbound must be on its guard for a car

turning from eastbound to northbound. The condition table spells out these "right of way" priorities that have been built into the program.

It is axiomatic (and not mentioned an the table) that no car can ever move into the next UB if another car is already in the next UB. Also, cross flow (at 90°) is routinely checked at intersections and is not covered in the table.

79
Appendix L

DETAILED MOVEMENT OF MARKED CARS 1 of 2 Appendix D is a reduction of the chain printout sheets as they came

off the computer after the simulation run. On these sheets are charted

the paths of the "marked cars". The first column represents time in ascending quarter seconds. The computer run began at time 1036, but

the portion shown begins at time 1201. Other columns show the successive unit block positions of marked cars referenced to the quarter second. Thus it is possible to trace through the movement of a marked car from beginning to end. For illustrative purposes, we will consider a car generated in time

1222 and launched in UB 2650. A connecting line has been super- imposed on the printout sheet to link the successive quarter-second

positions of this car. The launch time is unique and will serve as an identification of the car for tracing purposes. The Generation Table (Appendix A)

shows this car, noting that the exit is (13th Street), the desired

speed category is 2 (25 mph), it is type (passenger car), it is a marked car (otherwise we could not follow it), and it has a "1" lane preference (prefers lane 4 of 13th Street; "0" would indicate Lane 1).

If we follow the car's progress, we see it moving east along the north lane of Harvard Street. (See Fig. 2 for orientation on UB

numbers.) It slows for the 13th Street intersection and stops-at time , 1233 in UB 2666 to wait for a red light. Zigzags in the connecting line are of no consequence. They are caused by the fact that cars are processed in ascending order of their unit block number. Furthermore,

newly generated cars enter the list last and must then be rearranged in numerical order for their next processing.

Our car (No. 1222) waits until time 1307, when it starts up slowly. At time 1313 it swings into diagonal UB 3334 for the turn. It proceeds

into UB 1970 which is lane 4 of 13th Street. It gradually builds up

sp >ed until it approaches the next cross street (Columbia Road) where

it meets a red light at UB 2016. At time 1433, the light changes and

the car again accelerates toward its desired speed. At time 1465, our car shifts from 13th Street lane 4 to lane 3. This is indicated by the change in UB number of 600. The 13th Street lanes are numbered "modulo 600". An increase of 600 means a shift

to the left; a decrease of 600 means a shift to the right.

The reason for the lane shift is presumably another car in the way. We do not know what car because it is not a marked car. At time 1573 our car enters UB 1610, the Station B check point.

The Station B Count (Appendix B) can be referred to. We note our cai No. 1222 passing in time 1573 in lane 3. We note also that there are

80
Appendix L

2 of 2 various other cars in the immediate vicinity which might be

considered "ghost" cars because we have no other information as to their movements.

Our car No. 1222 continues up the street. At time 1600, it shifts back to lane 4 because of a ghost car. It finally reaches the last UB 2340 and retires.

If we look in the Vehicle Retirement Table (Appendix C), we

verify that our car No. 1222 was retired at time 1661. We note also

that its actual speed was 76 unit points per quarter second. When

converted (for approximation divide by 3) the speed is 25 mph which

is the original desired speed of No. 1222. Appendix C does not enter a running time in the last column because No. 1222 did not traverse

the full course of 13th Street. (It entered from Harvard Street.

)

81
APPENDIX M

I OF 2

S62 AHK.IF HAS STOPPED \

V^ (UN BIT 18) J

S64 S66

NO ADO STOP LINE TO CF

(CONFIRMED DISTANCE) LOOK UP REDUCED J

SGI2 YES S68A S66A

IDENTIFY UB 6ET INFO. PKG. PUT I IN BIT 18 J-0 ?

SET INDEX RE6ISTERS -4. « 20

FUOW CHART OF S6 2 STOP SIGN ROUTINE

-82
Critical Speed for Stop Sign Routine

Appendix M

2 of 2

No.

-Unit I of ilock

12

34

5

Critical J Q - A

A

A

A

Q

A

- 6 38

- 7 44

- 8 50

- 9 56

- 10 62

- 11 69

- 12 75

- 13 81

- 14 88

- 15 94

- 16 100

- 17 106

- 18 112

- 19 119

- 20 125

RCR 7 3B

LANE

DO

]Q

DDDD

D0D

DD0

0QD0

432 I

^

Q-l Q-2

Q-3

Q-18 Q-19 Q-20

J = jump in terms of unit points

per 1/4 sec. Critical J is based on "acceptable gap"

of 4 seconds (16 quarter -second

time intervals).

Sample computation

6 x 100 _ 16 i8

7 x 100 AA T5— = 44

A: Arbitrarily set at safety factor. as a

83
APPENDIX N

GET REDUCED JUMP

FROM TABLE

TEST J A6AINST MAX & DJ

GETPRES.POS.i

PUTIN PP M3B f SPOS r ? jYES

A RI6HT LANE SHIFT

N3A JHO M3C ( SPOS-8?

J- YES

DO A LEFT LANE SHIFT

H4 P

(

irreeub

.? )-^rC TURN ?

COMPUTE COMPOS

(IOO-PP) I M20 C J < COMPOS? ^

N

° » (" END BLOCK? J

M26 M20B

ADD J TO

lYES

PREPARE DATA FOR RETIREMENT TABLE

PICK UP SPOS AND MOVE CAR

130 j

M20I

RETIRE CAR

FLOW CHART OF Ml MOVE ROUTINE

84
A lane: L lane: LL lane: R lane: RR lane:

Appendix O

1 of 3 TERMS

(Accompanied by Symbolic Notation Used in Program)

Our own lane. Lane to the left of ours. Lane two lanes to left of ours. Lane to right of ours. Lane two lanes to right of ours.

Unit block (UB): All lanes are divided into consecutively numbered

sections 12 feet long.

Unit points: Each unit block is divided into 100 unit points. Thus one

unit point represents a distance equal to the hundredth part of 12 feet, or 1. 44 inches.

Our car (RCR): The car that is being processed.

reader (LDR): The car ahead of our car. Follower (FLW): The car behind our car. Present position (PP): Precise location of (nose of) car within. the

unit block, expressed in unit points.

Straddle position (SPOS): Refers to the lateral position of a car with

respect to its lane. When a car shifts lanes it passes through a series of intermediate lateral positions before the shift is completed. The successive intermediate positions and their designations are described in Appendix G on the "Two-Word

Format". (Refer to bits 8 to 10 in word 1.

)

Generation point: Cars are generated by random numbers and enter

the model at the beginning of each lane. If a generated car

cannot be safely launched it is saved in the "gate". Furthermore

a backlog is kept in case additional cars are generated which

cannot be launched.

Exit (EXIT): The exits are determined initially from a probability

distribution so set up as to produce the required volumes and

percentages of right-turn, left-turn and through movements at each intersection to correspond with the stated field counts at key points.

Desired speed (DJ): That speed at which a car will try to go. If a car

starts from rest and has a clear signt distance ahead, it will 85
Appendix O

2 of 3 accelerate at its permissible rate as determined by its type

until it attains its desired speed. Obstructions will of course

hold down the speed of the car but it will constantly strive to attain its desired speed whenever it can. The desired speed

is determined at the time the car is generated, according to an assigned probability distribution. (See Figure 16.)

Desired speed category (SPCAT): Car's desired speed is expressed

by a category designation. Five categories are included ranging

from 15 mph to 35 mph in 5 mph increments. Present speed (LJ): Expressed by the "last jump" (in unit points per

quarter second) and carried in the information about the car. Acceleration (ACL): A car's acceleration rate is keyed to its type.

(See Fig. 16, for assumed acceleration and deceleration rates.)

Move (J): Every quarter second each car is processed and makes a quarter second "jump" which can be translated into a mph speed.

(For approximate result, divide by 3.

)

Goal points (GP): Total net effective clear distance ahead that must be

achieved (analogous to sight distance) in order to permit a

particular move. Confirmed points (CF): Those unit points that have been cleared

ahead (by inspecting successive unit blocks) counting toward the required goal points.

Sight distance: Unobstructed space in front of a moving vehicle. If a

vehicle is moving at any specified speed, safety requires enough

clear road ahead to permit the driver to react in case of an

unexpected obstruction and to stop before collision, staying

within the physical limitations of a realistic deceleration rate.

(Fig. 15 is a table of stopping distances for different speeds.) Net clear distance ahead: Clear distance ahead (sight distance) after adjustment for the speed and length of a car ahead. If our leader

is going at least as fast as our car and is ahead of our car by at least the minimum clearance dictated by the leader's speed,

then he will not be an obstruction to our car even though he is fairly close. Clock: The simulation has two clocks. One (known as CL.K) starts over every time it reaches 320 quarter seconds. This is the length of traffic signal cycle. This clock is consulted to determine signal indications. The other clock (known as ABCLK),

also in quarter seconds, goes on indefinitely, and is used to define car running times and the duration of the simulation run. 86
Appendix O

3 of 3 Launch time: The time at which a car is safely launched on the street. The car carries its launch time with it. Being expressed in quarter seconds it is almost always unique and serves as an

identification of the car thereafter comparable to a license

number.

Turn bias: When a car is within 1200 feet (100 unit blocks) of an

intended turn, it will persist in trying to get in the correct lane

for the turn (right lane for right turn, left lane for left turn).

The first try will be to shift; if that is impossible it will proceed

in the A lane; under no circumstances will it shift lanes in the wrong direction. Last chance block: If a car with a turn bias is long enough unsuccessful in shifting lanes, it will ultimately reach a last chance block

which serves as a barrier beyond which the car cannot proceed

without shifting lanes. If necessary, the car will actually stop

and wait for a gap. Point of curvature: The geometric point at which a turning vehicle

leaves its original lane to begin a turn. Point of tangency: The geometric point at which a turning vehicle

completes its turn and resumes a straight course. Lane preference: The specialized meaning of this term is explained in the paragraphs headed "Turns" and "Lane Preference" in Chapter 8, "Details of the Program".

87
Appendix P

3 of 3 LIST OF SIMULATION RUNS

Run No, 1: From Time to Time 637. The computer halted after 637 quarter seconds of simulated time because of an error in processing one ox several hundred cars. At the beginning the layout was empty of cars. Run No. 2: From Time 637 to Time 1036. This was a test run of 400 quarter seconds to verify that the program error described above

had been corrected and to ensure that the model was full of correctly

performing cars. It utilized the final positions of cars in Run No. 1 as starting positions for Run No. 2. Run No. 3: From Time 1037 to Time 1996. This run was the "production run" of the desired 960 quarter seconds of simulated time

(covering three full 80 -second traffic signal cycles) to which the result figures in this report refer and which was used to make the movie. Initial car positions were taken from the final output of Run

No. 2. Run No. 4: Later it was possible to repeat Run No. 3 using as the starting positions the final output positions of the original Run No. 3 instead of those of Run No. 2. This run in essence represented

another "throw of the dice" in the Monte Carlo method. Also it possibly reflected a more "mature" full layout of cars. Since the layout was entirely empty of card at Time 0, the passage of several

traffic signal cycles after initial fullness might be advisable to produce stability.

Run No. 5: This run was similar to Run No. 4. It utilized the same

initial positions of cars (from output of Run No. 3) but the traffic signal setting at Columbia Road was altered by 5 seconds.

Run Nc. 6: Rerun of Run No. 5 using as initial car positions the output positions of original Run No. 5. Puns No. 1 and 2 were preliminary runs the principal purpose

of whic.i was to fill the model with cars. Run No. 3 was the "production run" used for the basis of this report.

Runs No. 4, 5 and 6 were made later to demonstrate the use of stochastic inputs and the facility for varying specific parameters.

There were no apparent errors in these additional runs. However, no

statistical examinations of the results were made because the purpose

at this stage was to demonstrate a working device rather than to derive statistically significant output values.

88
TI. S. DEPARTMENT OF COMMERCE

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