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GRIDLOCK.TXT
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1993-05-24
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file GRIDLOCK.TXT
================================================================
INSTRUCTIONS FOR GRIDLOCK
================================================================
Fred Lee
CONTENTS
INTRODUCTION ........................ 1
COMPUTER REQUIREMENTS ............... 2
THE FILES ........................... 3
STARTING THE PROGRAM ................ 3
YOUR SECTOR OF THE CITY ............. 4
MAIN MENU ........................... 4
Quit without saving (7) .......... 5
Quit this program (6) ............ 5
Turn sound off (5) ............... 5
Clear things (4) ................. 5
SET INTERSECTIONS (1) ............... 6
Type ............................. 7
Phase ............................ 8
Slave light ...................... 8
Slave delay ...................... 9
Demand ........................... 9
Normal-time demo ................. 9
Copying intersections ............ 9
Paper work ....................... 10
PLAN A TRIP (2) ..................... 11
RUN (3) ............................. 12
Traffic .......................... 12
Day or night ..................... 12
Mall lights ...................... 12
Running .......................... 13
Accidents ........................ 14
Speed ............................ 14
Time clock ....................... 15
Test cars ........................ 16
HOW THE CARS BEHAVE ................. 16
HINTS ............................... 18
Re-starting the RUN mode ......... 18
Car-speed facts .................. 18
Synchronizing .................... 18
CONCLUSION .......................... 19
INTRODUCTION
Did you ever think, when you were out there driving in the
traffic, that you could set the traffic lights much better than
the clowns who are paid to do the job? You probably think that
your parakeet could do it better. Well, here's a chance to see
what you can do. GRIDLOCK gives you a whole section of town, the
Morass district in the great metropolis of Quagmeyer City, PU,
with lots of cars driving around in it. You can decide what kind
of lights or stop signs to put at what intersections and you get
to set the lengths of the cycles. Your district consists of some
eleven avenues crossed by twelve streets and one expressway.
(There is a common misconception that it's called an expressway
because you can zip along on it at high speed and not have to
stop at a lot of red lights. So when you find yourself poking
along it in bumper-to-bumper traffic and being stopped - maybe
two or three times - at every intersection, you tend to invent
all sorts of new ways to express your feelings. And that's why
it's called an expressway. On a good day, you can see thousands
of drivers all in a row muttering a fantastic variety of
expressions.)
You can look at the game in two ways. You can try to design
systems that will make traffic flow as smoothly and quickly as
possible. Or, if you think that you might want to apply for a
job with your city's Department of Setting Traffic Lights, you
can practice setting lights in such a way that every car will get
to every intersection just as the light turns red and just
generally foul up the traffic and achieve - - - gridlock.
There are two ways to measure your success or failure as a
traffic designer. One way is to see whether you can get maximum
(100%) traffic to flow without getting hopelessly blocked
intersections, accidents, and police cars out in force. That
isn't easy to do. Even if you succeed for a while, sooner or
later, something could go wrong. Maybe a more realistic test
would be to see how long you can run at maximum traffic before
something bad happens. The other way to measure your success is
to see how long it takes for one of your test cars to go from
point A to B under different traffic conditions.
You can try your ideas on the normal traffic in your sector.
The computer controls these cars. The only thing you can control
is the number of cars that are driving around. There are also
two special cars, called test cars, that you CAN control. You
1
get to program their routes and the computer times their trips
for you. The test cars are your only means of accurately
comparing different systems. That is, of course, by running the
same test routes with the different systems of traffic controls
and seeing which take more time. (The computer automatically
generates appropriate expressions for the drivers of the test
cars to mutter. But due to certain regulations, they cannot be
put on the screen or printed out.)
Being a computer simulation, this town is not a hundred percent
realistic. Unlike yourself, the cars obey the speed limit. They
don't try to beat the red light the way you would. They do
sometimes make left turns on yellow lights, though. Especially
if they have been prevented by oncoming traffic from turning when
the light was green.
There are no pedestrians. So there are none of those
buttons that slow down a light so that even a very old lady on
crutches can make it across and have time to get home, cook
herself a cup of tea, and drink it before the light comes back to
life. Of course, with no pedestrians, there is no way of hitting
one. Sorry about that. But cars can occasionally hit each
other.
The program is run from menus and most things that you have to do
are explained right on the screen so that you should be able to
blunder your way along. For the three of you who actually read
instructions, the following pages give you more detail than you
get on the screen.
The traffic in GRIDLOCK drives on the right side of the road.
That means the game would not be useful in, say, England, where,
as the great writer Dave Barry reports, they drive on both sides.
Ironically, it will also not be popular in Japan where most of our
cars are made.
COMPUTER REQUIREMENTS
To run GRIDLOCK takes an IBM (or compatible) computer with at
least 512K of RAM and EGA or VGA color graphics. Computers with
clock speeds of over 16 MHz run the program at full speed. Below
that speed, as speeds drop lower, the action slows down. The
slow-down is hardly noticeable at 12.5 MHz. Below that speed it
becomes more and more apparent.
2
THE FILES
The GRIDLOCK disk holds the following disks:
README The first thing you should read
GL.EXE The main gridlock program file
GRIDLOCK.RTS Stores car routes
GRIDLOCK.DAT Stores all traffic conditions
GRIDLOCK.DOC This instruction file (ASCII text)
The .RTS, .DAT, and .EXE files must be on the same disk drive
when the program file GL.EXE is being run.
STARTING THE PROGRAM
The GRIDLOCK program is in the file GL.EXE. It can be run from
the hard disk or a floppy. The data files GRIDLOCK.RTS and
GRIDLOCK.DAT must be on the same drive as the .EXE file.
To run, get the prompt of the drive you want to use and enter GL.
That starts the program which then reads the two data files. One
of these, .DAT, stores the conditions and settings that were in
use the last time the program was run and was terminated with
option 6 (Quit this program) of the main menu. That allows you
to continue the program as it was when you left it.
If you don't want to continue the program as it was when you left
it, start the program by entering GL SKIP instead of GL. That
causes the program to skip the reading of GRIDLOCK.DAT so that
the conditions such as traffic light settings and cars on the
road will all be cleared when the program starts. This way of
starting takes less time.
If you want to save a number of your solutions to the traffic
problem, one way to do it is to start each time with a fresh
diskette that contains the .EXE, .RTS, and .DAT files. When you
have finished, put the entire diskette away (after labeling it
appropriately) and use a new disk for the next solution. Another
way is, when you have finished one solution and quit the program
with option 6 of the main menu (the one that saves the conditions
in the file GRIDLOCK.DAT), to copy the file GRIDLOCK.DAT to a
file with some other name (for example, GRIDDATA.001). Then the
next time you want to play with this solution, copy it back to
the file GRIDLOCK.DAT before starting the program.
3
YOUR SECTOR OF THE CITY
Figure 1 at the back of these instructions is a crude map of the
Morass district of the city. (You might make copies of this map
or the much better map that you get when you pay for the program.
The copies can be used to keep paper records of your traffic
light systems or your test routes. And it might be easier to
design your systems and your test car routes on paper before
entering them on the computer.)
There are twelve streets running east and west. They are named A
Street to L Street. Between K and L streets there is an
expressway labeled X.
Running north and south are eleven avenues named 1st Avenue to
11th Avenue.
There is a mall and a park. Roads run into them but do not run
through them.
Each intersection is marked with an x. note that there are only
three intersections on the street X, the expressway. The other
crossings on the expressway are underpasses.
The numbers at the top and the right of the map show the number
of lanes in each road. If there is an odd number of lanes, the
center lane is used for left turns only.
MAIN MENU
The first menu you will see is the main menu. You can return to
this menu from any point in the program by pushing the F1 key.
(You might have to push F1 more than once if you are more than
one menu away from the main menu.) The Esc key also gets the
main menu. The main menu looks like this:
MAIN MENU
1 SET INTERSECTIONS
2 PLAN A TRIP
3 RUN
4 Clear things
5 Turn sound off
6 Quit this program
7 Quit without saving
4
The first three choices are the main activities. That's why they
are capitalized. They will be explained in the next three
chapters. The other choices are the supporting activities which
will be explained in this chapter. But they are easier to
explain if we start at the end and work backward.
Quit without saving (7)
Quit without saving lets you quit the program without putting the
current traffic, traffic light settings, and test car routes onto
the disk (the file GRIDLOCK.DAT). So the next time you start the
program, it will start with any conditions that you had
previously saved on the disk. If you don't care one way or the
other, this is the faster way to quit.
Quit this program (6)
Quit this program lets you quit the program AND save the current
traffic, traffic light settings, and test car routes on the disk
(in the file GRIDLOCK.DAT). So next time you start the program,
it will be as though you are continuing exactly where you left
off when you quit.
Turn sound off (5)
Turn sound off lets you turn off the occasional beeps that the
program produces. The menu will then say "Turn sound on" and you
can turn sound on again.
Clear things (4)
Clear things lets you clear anything that you might want to
clear. If you select this choice, you get the following menu:
1 Clear green test car route
2 Clear magenta test car route
3 Clear traffic light settings
4 Clear traffic from streets
5 Return to main menu
Whatever you clear with these selections will be cleared when you
return to the RUN mode of the program. But the conditions stored
on the disk will not be affected. If you want to clear what is
stored on the disk also, you have to do your clearing and then
quit the program using selection 6 of the main program.
(There is also a way to start the program with all of these
conditions cleared even if they are not cleared on the disk.
Instead of entering GL to start the program, enter GL SKIP.
That tells the computer to skip the reading of the disk file
GRIDLOCK.DAT.)
Now for the explanations of the three main choices of the main
menu.
5
SET INTERSECTIONS (1)
This first item of the main menu lets you decide what kind of
controls to put at each intersection and to set the timing. Of
course, these choices depend on how much traffic the intersection
has to handle. That depends somewhat on the width of the streets
but also on which part of town they are in. You should put the
program into the RUN mode and watch the traffic until you see
where it normally flows and where it is the heaviest. It is a
little harder to learn, by watching, where the most left turns
are made so that you can decide on what kind of turning lights to
put. Table 1 at the end of these instructions can be helpful
there. It lists the numbers of left turns made at all
intersections by a sample of 200 car trips. The turns are listed
by the directions that the cars were driving before the turns.
Those who pay for the program will get a map with these numbers
on it. It is much easier to use than Table 1.
If you watch the traffic for a while, you will see how cars
behave at intersections that have no traffic controls at all.
Cars on a smaller road approaching a bigger one will tend to wait
until it's clear before crossing. The cars on the bigger road
will take the right-of-way. If the roads are of equal size,
where there are more cars waiting, they will tend to go first.
Turning cars go pretty much when they can. Since the cars are
not controlled, there is a small chance of an accident at these
intersections.
The first screen you see in this SET INTERSECTIONS mode asks you
to select an intersection by typing first the number of the
avenue and then the letter of the street. (You will notice that
the computer does an annoying little hesitation before it
responds when you type a 1. That's because it wants to be sure
whether you are just entering a 1 or trying to enter a 10 or an
11. So if you are entering 10 or 11, enter the second digit
without waiting for the computer to respond to the first. If you
are entering a 1, be patient. The computer will realize it in a
second or so.)
The next screen then shows a square in which you can make your
selections. To the right of the square is a picture of the
intersection drawn in such a way that you can see the number of
lanes in each road. This picture will illustrate the traffic
lights and the traffic flow as you make your selections. The
selections you can make are as follows:
6
Type
You can select one of the ten types on the table shown below.
Don't worry about having to remember all of those many types and
phases. The computer will illustrate them for you while you are
setting them.
Type Phase Description
---- ----- ---------------------------------------
0 No stop signs or lights
1 Stop signs for N and S directions
2 Stop signs for E and W directions
3 Stop signs for all four directions
4 1 N and S green lights (turns ok if clear)#
2 E and W green lights (turns ok if clear)#
5 1 N green and N left-turn lights
2 S green and S left-turn lights
3 E and W green lights (turns ok if clear)#
6 1 N and S green lights (turns ok if clear)#
2 W green and W left-turn lights
3 E green and E left-turn lights
7 1 N green and N left-turn lights
2 S green and S left-turn lights
3* E left-turn and W left-turn lights #
4 E and W green lights (no turns)
8 1* N left-turn and S left-turn lights #
2 N and S green lights (no turns)
3 W green and W left-turn lights
4 E green and E left-turn lights
9 1* N left-turn and S left-turn lights #
2 N and S green lights (no turns)
3* E left-turn and W left-turn lights #
4 E and W green lights (no turns)
* Only if there is demand for the lights
# Turns continue through 2/3 of yellow light
A more graphic chart of these types will be sent to you if you
buy this program. It makes things much clearer.
7
After you select the type, the cursor does not automatically
advance to the next item as it does for the other selections.
That allows you to watch the picture at the right of the screen
demonstrate the "type" you have selected and, if you aren't happy
with that type, lets you change it any number of times without
having to move the cursor back each time. When you are ready to
continue, push Tab or PgDn to move the cursor. (PgUp moves it
up.) The computer then puts into the square the other items and
settings that are appropriate for that particular type.
Phase
Next, you can assign the number of seconds that the green light
will stay on in each of the phases. Move the cursor to the phase
that you want to change. Note that the picture on the right now
illustrates the traffic flow at only this particular phase. Type
a number and push ENTER. The computer automatically puts a
three-second yellow light after each green light. Be sure to
take that into account when you calculate the total time of the
cycle. (When you calculate how much time to allow for left
turns, don't forget that, in certain phases, turns continue to be
made for two seconds or so after the light turns yellow.)
Slave light
You can use this item to synchronize lights. Any other
intersection that you designate here will become a slave and this
one (the one you are now programming) becomes the master. That
means that the slave intersection will be made to start its first
phase when the master starts its first phase. Of course, it's
best to program the phases of the two intersections to be the
same. At least the total time of all of their phases should be
the same. (When calculating the total time, don't forget to add
a three-second yellow light after each phase.)
If you want to synchronize more than two intersections, the
second one must be programmed to be the master of the third, the
third must control the fourth, and so on. It is best (but not
absolutely necessary) that a slave intersection be to the east
(right) and/or south (below) a master.
If you don't synchronize intersections, the computer purposely
distributes the starting times of their cycles randomly. If you
want to introduce even more randomness, you can, of course,
program the total cycle-times of lights to be different.
8
Slave delay
Any number you put here will be the number of seconds by which
the slave intersection lags the master. For example, if you
enter a 10, the slave intersection will be made to start its
first phase ten seconds after the master starts its firs phase.
If you leave this item at zero, the lights should switch
simultaneously.
Demand
This is a 'yes or no' choice. If you say 'yes' here, a green
light will be terminated if there is no more demand for it and
there is demand in other directions. (If you are wondering how
the light senses the presence of cars, notice that there
occasionally are gray lines across the roads. Those are car
sensors.)
Since the demand feature can shorten the duration of the light
cycle, we wouldn't want to use it if the intersection is
synchronized with another. The computer doesn't let you say
'yes' here if the intersection has been programmed to have a
slave. It's up to you to see that you don't ask for demand if
the intersection is a slave to another.
If the type of traffic light that you have chosen has a turn-only
light phase, demand is automatic. That is, the turn lights won't
even come on if there is no demand for them. But in this case,
the total cycle time is not affected. The extra time is given to
the next phase.
Normal-time demo
After you have moved the cursor through all of the selections, it
will turn into an arrow pointing to the picture and the right and
say "Normal-time Demo". The picture then illustrates the light
cycle with the times as you have assigned them. When you are
satisfied, you can push F1 to select another intersection to
program or you can make more changes by moving the cursor.
Copying intersections
When you have finished programming an intersection (or, if you
have already pushed F1, you can bring the information back to the
screen by just selecting the intersection again), you can copy
the settings you have made to an adjacent intersection just by
pushing an arrow key. For instance, pushing a right arrow,
selects the intersection to the right and puts the same data in
it. The only settings that will not copy from one intersection
9
to another are the Slave Light, Slave Delay, and Demand. They
will copy over as no slave, 0 delay, and no demand. If you then
want to change them, you can. The computer automatically skips
any intersections that don't exist (because of the park or mall)
and that are underpasses.
Even if you don't plan to assign each intersection on a street
the same traffic controls, it might save time to set an
intersection at one end, copy it along the entire street, and
then change those intersections that you want to be different.
Paper work
If you like to plan your systems or record them on maps of the
district, the following procedure is recommended. At each
intersection, write your settings as illustrated below.
|
| Duration
Type | Phase 1 and 2
|
------------------------- street
Slave/delay |
or | Duration
Demand | Phase 3 and 4
|
avenue
For the Type, put a number. For the Slave/delay entry, write the
slave station and the delay as, for example, 5G15. If you
program Demand there instead of a slave light, put the letter D.
In the Duration spaces write the durations like 10/15. Here are
some sample intersections.
| | | | |
4 |10/10 3 | 9 | 8/15 | 5 |7/8
---------- ----------- ----------- --------- -----------
D | | | 5/15 | 6E0 | 7
| | | | |
If you buy this program, you will receive a map of the area with
a fairly well designed traffic system on it using the symbols
above. If you are having trouble designing a good system, it
will help you. Or you might be able to make improvements on it.
10
PLAN A TRIP (2)
This second item of the main menu lets you program the routes of
the two test cars. So that you can easily spot them on the
roads, test car 1 is bright green and test car 2 is magenta. The
first screen that you see asks you to select one of these test
cars by pushing 1 or 2. You don't have to program any test cars
if you don't want to. In fact, it will save time to first use
only the normal traffic to test any new traffic light set-up.
If you do select a test car, you are given a table in which you
can enter up to ten roads and directions. There is also a map of
your section of the city. Any route that you program will begin
at an edge of this section and end at an edge unless you program
it to go into the mall or the park. The directions on the screen
tell you how to make your entries. When you have finished
entering a route, push the F1 key.
An example of a route might look like this:
Road Direction
X east
6 north
G east
11 north
D west
4 north
This trip starts on the expressway at the left edge of the map.
The car then turns left on 6th avenue and right on G street. It
goes around the park, heading west on D street. Finally, it
turns into the mall at 4th.
The computer tries to prevent you from putting in directions that
don't make sense. Depending on your error, it either doesn't
respond at all or gives you an error message. When you push F1,
it analyzes the route again and gives you a message if it still
finds a problem.
(By the way, when you enter avenues, you will again notice that
annoying little hesitation before the computer responds when you
type a 1. That's because it wants to be sure whether you are
just entering a 1 or trying to enter a 10 or an 11. So if you
are entering 10 or 11, enter the second digit without waiting for
the computer to respond to the first.)
11
RUN (3)
In this third item of the main menu, you get to test all of the
things that you have programmed in the first two modes.
Traffic
The first screen lets you set the amount of traffic. The number
you enter is the percentage of maximum traffic. You can select
anything from 0 to 100 percent. The maximum traffic is 998 cars
(which becomes 1000 if you add the two test cars).
Then you are asked to decide whether you want everything to speed
up before the amount of traffic you have asked for is on the
screen. If the computer is very slow, you won't see much
difference. With a fast computer, it can shorten the time you
have to wait for the traffic to become normal. If the computer
is too fast, you might not like the effect. You will have to try
both ways and see which you like better.
Day or Night
The next screen lets you set day or night. At night you see only
the headlights of cars. So if you select night, cars (except for
the test cars) will all be bright yellow. You can't distinguish
one car from the next if they are close together. If you select
day, cars will have a small variety of colors but they will be
harder to see. The choice is up to your personal preference and
might depend on how good your color monitor is.
The next screen is the main screen that shows the roads with all
of your intersection controls, the mall, and the park.
Mall lights
Not long after things start to run, you will see a row of little
square lights of various colors at the bottom of the mall area.
Not every player will be interested in them but this is a good
place to explain what they are. They are a way of putting some
numbers on the screen without taking up much room. So they are
codes. There is a group of two dots on the right and a group of
four on the left. The group of two has to do with how long it
takes the computer to move all cars and service all lights. More
about that when we get to the paragraph on Speed. The group of
four lights is the number of cars on the screen. The number is
like a normal decimal number except that the digits are color
coded using the code that was used to mark electrical resistors
when they were still big enough to see. The code is as follows:
12
0 black 5 green
1 brown 6 blue
2 red 7 violet
3 orange (red and yellow) 8 gray
4 yellow 9 white
For example, black, green, orange, and brown would be 531.
You're not expected to learn this code. You might find the
lights useful anyway because they show whether the number of cars
is changing or has stabilized. Or you can just consider the
lights to be decorations for the mall.
Running
The computer controls the routes of all of the cars except the
two test cars. The computer has a large number of pre-programmed
routes to chose from. It selects from these routes at random so
that the traffic is entirely different each time the RUN mode is
run. The things that are similar in different runs are the
statistical patterns. That is, the traffic tends to be heavier
in some areas, there tend to be more cars on the bigger roads,
and there are more left turns at some intersections than at
others.
At the start, there are no cars. All cars come into the sector
from the edges. If you elected to let the computer do it, it
attempts to speed things up (if the computer is fast enough to be
able to do that) by running cars and lights as fast as possible
until amount of traffic is what you have specified. Then it
switches to normal speed.
At that time, you will hear three beeps and, if you have
programmed any test cars, they will start their trips. (in that
case, there would be another beep for each test car). The
numbers of minutes the test cars have been running are displayed
in the park area. The display is updated only once each minute
because the computer is very busy at that time. When a test car
finishes its run, the total time of the trip is displayed to the
tenth of a minute. Any time a test car is not already running,
you can start it yourself by pushing the space bar (or most other
keys).
Pushing F1 gets the main menu. If you then go back to the RUN
mode without doing any clearing in the meantime, things will
continue from where they were when you pushed F1.
13
Accidents
It is possible for cars to crash. A crash is most likely to
happen in heavy traffic, at an intersection with no traffic
controls (type 0), and where both roads are the same width.
Another likely spot for a crash is at an intersection in which
traffic has backed up due to another intersection having a
problem or just not being able to handle its traffic. Unless you
happen to be looking in just the right spot when it happens, you
will first notice an accident by the backup of traffic around it.
Some time after an accident a police car should appear. You can
recognize it by its rotating blue light. The police also
sometimes appear if an intersection is clogged due to a problem
at another intersection. Sometimes the cops can un-clog an
intersection and go away after a while. Sometimes there is no
way to clear an accident scene except to push F1, clear the
traffic, and start the run over again. (The computer tries to
keep on the screen the total number of cars that you specified.
So if a lot of cars are stuck at accident scenes, fewer cars will
be driving around.)
Speed
The computer should be able to do one cycle of moving every
car once, servicing every traffic light, and doing a few other
things (like starting new routes and stopping old ones) in less
than half a second. If a computer is fast enough to do that and
you have elected to let it, the computer is allowed to run as
fast as it can until the required numbers of cars are on the
screen. After that, if it finishes a cycle before a half second
is up, the computer waits until it is up before starting the next
cycle. In other words, a fast computer will do one cycle every
half second. One block along a street (a long, horizontal block)
is a tenth of a mile long. A car takes an average of 29 half-
second steps to travel one block. So the speed of a normally
moving car, except on the expressway, is 25 miles per hour. on
the expressway, the speed is 50 miles per hour.
If a computer is too slow, or becomes too slow as the number of
cars on the screen increases, everything - cars and traffic light
cycles - slows down. You begin to see the scene in slow motion.
You can get a reading of how much things are slowed down from the
two light dots at the right end of the row of dots at the mall.
The dot on the left side of the pair is black. It will stay
black unless the cycle gets to be over 5 seconds long. As long
as one cycle takes a half second or less, the dot on the extreme
right end is brown. If it takes longer than a half second
(actually 0.6 seconds) the light becomes red, and so on. The
table below shows a few more of the colors and what they mean.
14
Time of a cycle Color Number
---------------- ------ ------
0 to 0.6 sec brown 1
0.6 to 1.1 sec red 2
1.1 to 1.6 sec orange 3
1.6 to 2.1 sec yellow 4
2.1 to 2.6 sec green 5
2.6 to 3.1 sec blue 6
3.1 to 3.6 sec violet 7
and so on
The program has been tested with computers of various speeds.
With the worst traffic and the most traffic lights, the following
cycle times were normal.
Computer speed Worst-case cycle time
--------------- -------------
5 MHz 3.4 sec
12.5 MHz .75 sec
16 MHz and above .50 sec
There is some slow-down at 12.5 MHz but it is not noticeable.
Time clock
At the top right side of the screen (between 10th and 11th
avenues), there is a number that shows how long the RUN mode has
been on. If you stop the RUN mode, the timing also stops so
that, if you start the RUN mode again, the count continues from
where it stopped. The only exception to that rule occurs if you
clear the traffic before starting to RUN again. The count is
then reset. So actually, it is a timer that shows how long the
traffic has been running.
This timer really counts computer cycles - a cycle being what it
takes to move all of the cars once, service the traffic lights,
etc. Actually, the number displayed on the screen is the number
of cycles divided by 120. So if your computer is fast enough to
do one cycle in half a second, the displayed number represents
minutes.
If the computer is too slow, the count also slows down and
no longer indicates minutes but something longer. By the same
token, if you start the run mode and ask the computer to move
cars as fast as it can until the designated amount of traffic is
on the screen, the count will speed up if the computer can move
all cars in less than a half second. In that case the count will
represent something shorter than minutes until right amount of
traffic is on the screen. In either case, the number can still
provide a useful measure of how long traffic has been running.
15
Test cars
Any test car routes that you have programmed begin automatically
when the traffic reaches the amount that you have set. Or you
can start the test cars by pushing a key. There will be a beep
when a test car starts. In the park area, a number appears for
each test car that indicates how long the test car has been
running. If you push F1 to get the menu and then go back to the
RUN mode, everything continues as it was before EXCEPT FOR THE
TEST CARS. The test car trips are stopped and start over again
when the RUN mode is resumed.
As in the case of the time clock described in the previous
section, the timer that times the trips of the test cars counts
cycles and divides them by 120 before displaying them. That
means that the times shown in the park area are in minutes as
long as the computer is fast enough to do one cycle in half a
second. While the test cars are running, the time is updated
only once each minute because the computer is very busy at that
time. But at the end of a test car route, the total time of the
trip is displayed to the tenth of a minute.
if your computer is too slow and slows everything down,
the timer that times the test cars also slows down. In that
case, if you were to time a trip with a clock also, the results
would not agree. (For example, if the computer takes an entire
second to move all cars, a real clock reads two minutes when the
computer's timer reads one minute.) The good thing about this
method is that, under the same traffic conditions, you will get
the same readings on slow computers that you would on computers
that are fast enough.
HOW THE CARS BEHAVE
It will be useful for you to know what rules the computer
normally follows in driving the cars along the roads. (Some of
the rules have been mentioned before.) Rules that are obvious
will not be repeated. For example, that cars will stop at red
lights and go on green, or that they will stop at stop signs, and
so on. Of course they will do those things. Even you probably
would. Most of the time.
All cars
These rules apply to cars that are going straight across and
intersection as well as those which want to turn left.
At intersections with traffic lights, cars will be guided by the
lights. Any special things that you should know are explained
below. 16
Where there are two-way stop signs, each car will come to a stop
and then proceed if there is no close cross traffic coming.
(Actually, if no car has reached the gray sensor line across the
street.) The case of cars turning left is described below.
You will notice that, if there are many cars in line at a stop
sign, out of consideration for the cars behind them, cars won't
stop as long. (In real life they would stop longer thinking, "I
had to wait a long time to get here. Now I'll take my sweet old
time and you can all wait".)
At four-way stop signs, each car will come to a stop and then
proceed when its turn comes. The turn alternates between N-S
and E-W so that an east and a west-going car could cross and then
a north and a south-going car. A car that arrives at an
intersection first generally gets to go first.
At an intersection with no controls, cars on a smaller road
approaching a larger one will proceed only if there is no close
cross traffic coming. Otherwise they will stop and wait until
there is no close cross traffic before proceeding. Cars on the
larger road will proceed full speed. If the two roads at an
intersection are the same size, the direction where more cars are
coming will go first. If the traffic is equal, the E-W going
cars will tend to proceed and the N-S cars will wait for an
opening in the traffic.
Straight-going cars
Cars going straight through an intersection will stop when the
light turns yellow.
At a stop sign, a car will come to a stop and then proceed across
if it is its turn. However, if the car going the opposite
direction wants to turn left, the right-of-way alternates between
the two directions.
Left-turning cars
At a traffic light where both directions have green lights and
there are no turning lights but turns are allowed, a turning car
in a turning lane will wait until there is no oncoming traffic.
If it has to wait until the yellow light, it will turn then. On
a two-lane road where there is no turning lane, the computer
crosses its fingers and lets the turning car turn even if there
is oncoming traffic. Otherwise, a car trying to turn at a busy
intersection, could permanently block the traffic behind it.
At intersections with turn-only lights, cars do continue to turn
for some two seconds after the lights become yellow. The
reasoning is that these are probably intersections where a lot of
17
cars want to turn left and it would be better to get them on
their way before they start to block the traffic behind them.
That's more or less the way it is in real life.
When cars going in opposite directions have stop signs and some
cars are turning and others are not, the right-of-way alternates
between the two directions.
At an intersection with no controls, turning cars don't hesitate
to cut in front of cars coming the opposite way.
HINTS
Re-starting the RUN mode after changing a light
If you have a lot of traffic on the screen, stop the RUN mode to
change a traffic light, and then re-start the RUN mode, there is
a small chance that cars in the changed intersection could find
themselves in trouble and have an accident. To prevent that, it
would be a good idea to clear the traffic before you re-start the
RUN mode.
Car-speed facts
When setting traffic lights, remember these facts. If your
computer is fast enough to run things at normal speed, each car
moves every half-second. So for a car that travels un-impeded,
* It takes an average of 14 moves to cover a short (N-S) block
* That means it takes about 7 seconds to go a short block
* It takes an average of 29 moves to cover a long (E-W) block
* That means it takes about 14.5 seconds to go a long block
* On the expressway, one block takes about 7 seconds
If you use these numbers to calculate the lengths of your light
cycles and your computer is not fast enough to run things at
normal speed, you don't need to worry. It's all right because
when the cars slow down, so do the traffic light cycles.
Synchronizing
If you want to synchronize a string of lights, consider making
the delay between synchronized lights equal to the time it takes
a car to go from one to the other and making the total cycle time
of the lights equal to twice that time.
18
CONCLUSION
Maybe when you have finished playing GRIDLOCK, you will be able
to answer the key questions here. Is it really as hard as it
seems to set lights in a way that keeps traffic moving? Or is it
impossible? If you were an oil company, would you really like
to see cars spending a lot less time sitting at red lights? If
you were an old lady on crutches, would you push that button?
Would you let your son or daughter marry one of those people who
set traffic lights? And how many of them does it take to change
a light bulb in one of those traffic lights? And what is red and
red and red and red and green and yellow and red and red and red
and red and red all over? Please don't send in your answers.
These are only retorical.... ritorical.... rhetor..............
This is not a quiz. No prizes. If you must send them in, send
them to your local traffic department. Thank you.
19
Figure 1. Map of your sector of the city
Lanes: 2 2 5 2 2 3 2 2 5 2 3 ___
|
| | | | | | | | | | | |
A --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
B --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
C --x-----x-----x-- MALL --x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
D --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 5
| | | | | | | | | | |
E --x-----x-----x-----x-----x-----x-----x-----x-----x-- --x-- 2
| | | | | | | | | PARK |
F --x-----x-----x-----x-----x-----x-----x-----x-----x-- --x-- 2
s | | | | | | | | | | |
t G --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 3
r | | | | | | | | | | |
e H --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
e | | | | | | | | | | |
t I --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
s | | | | | | | | | | |
J --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
K --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
X --------------x-----------------x-----------------x-------------- 7
| | | | | | | | | | |
L --x-----x-----x-----x-----x-----x-----x-----x-----x-----x-----x-- 2
| | | | | | | | | | |
1 2 3 4 5 6 7 8 9 10 11
avenues
20
Table 1. Left turns made in sample of 200 car trips
AV ST E W N S AV ST E W N S AV ST E W N S
1 A - 4 - - 4 J - - 1 1 8 E 2 1 1 1
1 B - 4 - 1 4 K - 1 - 2 8 F 2 - 1 -
1 C - 2 - 2 4 X - - - - 8 G 2 - 2 3
1 D - 6 - 5 4 L - - - 1 8 H 1 1 1 1
1 E - 1 - 1 5 A - 3 2 - 8 I 1 1 1 -
1 F - 1 - 1 5 B 1 2 6 1 8 J 1 - - 1
1 G - 4 - 8 5 C - 1 1 1 8 K 2 - 1 2
1 H - 2 - 1 5 D 2 2 2 3 8 X - - - -
1 I - 2 - 1 5 E 2 1 3 1 8 L 1 - - -
1 J 1 1 - 2 5 F 1 1 1 1 9 A - 1 4 -
1 K - - - 3 5 G 3 1 1 1 9 B 1 2 5 -
1 X - - - - 5 H 1 - - 1 9 C 1 1 1 -
1 L - - - 3 5 I 1 - 1 1 9 D 7 5 12 2
2 A - 2 1 - 5 J - - - 1 9 E 1 - 2 2
2 B - 3 1 1 5 K 1 - 1 1 9 F 1 - - 3
2 C 2 1 1 1 5 X - - - - 9 G 9 3 4 5
2 D 2 4 1 2 5 L 2 - - - 9 H - 1 2 1
2 E - 1 1 1 6 A - 4 7 - 9 I 3 1 - 1
2 F - 1 - 3 6 B 1 4 10 - 9 J 3 1 1 2
2 G - 2 2 4 6 C 1 1 1 1 9 K 2 - 1 1
2 H 1 1 1 1 6 D 4 6 6 5 9 X 12 4 7 3
2 I 1 1 1 1 6 E 3 1 2 1 10 L 4 - - 1
2 J 2 - - 1 6 F 2 - 1 1 10 A - - 1 -
2 K 1 - - 1 6 G 9 5 5 5 10 B - - 1 -
2 X - - - - 6 H 2 2 1 1 10 C - - - -
2 L - - - 2 6 I 1 1 2 1 10 D 2 2 - 1
3 A - 5 2 - 6 J 1 - 1 1 10 E - - - -
3 B - 14 4 2 6 K 3 2 1 2 10 F - - - -
3 C 2 - 3 8 6 X 9 6 5 9 10 G 2 - 1 -
3 D 4 13 9 10 6 L 3 - - 1 10 H 1 1 1 -
3 E 1 2 1 1 7 A - 1 2 - 10 I - - 2 -
3 F 3 1 2 2 7 B 1 1 3 1 10 J 1 1 1 -
3 G 5 4 3 10 7 C 1 1 - 1 10 K 1 - - 1
3 H 1 1 2 1 7 D - 3 1 1 10 X - - - -
3 I 2 1 1 2 7 E 1 2 1 1 10 L 1 - 1 -
3 J 2 3 1 1 7 F 2 1 1 2 11 A - - 2 -
3 K 3 1 - - 7 G 1 1 - 2 11 B - - 1 -
3 X 6 7 2 12 7 H 2 1 - 1 11 C - - 3 -
3 L 2 1 - 5 7 I 1 - 1 1 11 D 3 - 9 -
4 A - 4 1 1 7 J - - 1 2 11 E - 1 - -
4 B 1 3 - 1 7 K 1 1 - 1 11 F - - 1 -
4 C - - - - 7 X - - - - 11 G 7 - 2 -
4 D 6 2 2 - 7 L - - - 1 11 H 1 - 2 -
4 E 1 2 1 1 8 A - 1 2 - 11 I 3 1 1 -
4 F 1 2 1 1 8 B 1 2 2 - 11 J 1 - 1 -
4 G 1 1 - 1 8 C - 1 - - 11 K 3 - 1 -
4 H 1 1 - 1 8 D 1 1 2 1 11 X - - - -
4 I 1 1 1 2 21 11 L 1 - - -
